This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

SNOMED CT uses the Foundation Model of Anatomy (FMA) definition of body part and body part subdivision for some concepts. For example, the joint regions discussed below are classified as body part subdivisions, since that is what is intended by the diseases and procedures that use these terms in their definitions. They are not body parts because they are defined, not by a set of bones, but rather by a particular joint and its surrounding structures. However, our interpretation of the word region is based on common usage and is intended as a three-dimensional structure, not the FMA two-dimensional definition of body region. In other words, these regions are not simply surface regions (skin), but also include the three dimensional underlying structures (subcutaneous tissues, bones, muscles, tendons, fascia, vessels and etc.).

Surface regions

Many concepts contain the phrase surface region. These could be interpreted as massless (immaterial) mathematical surfaces, but a clinical terminology would have no direct use for such meanings in clinical records. They could be interpreted as having mass (not immaterial), but the depth then is arbitrary. Should it be just skin deep, or should it include deeper layers of the surface? If only skin deep, the meaning of these concepts would overlap with concepts for skin regions. If deeper, the meaning would possibly be the same as the generic structure concepts.

Abdominal regions

The named regions of the abdomen are by tradition divided horizontally by the transpyloric plane and the interspinous plane, and vertically by the midclavicular plane. The lateral regions are therefore bounded above by a plane that is inferior to the ribs. In contrast, the flank is the lateral region of the abdomen bounded above by the ribs. Thus some parts of the hypochondriac regions, which are superior to the transpyloric plane but inferior to the ribs, would be considered also part of the flank. The hypogastric region is also sometimes called the pubic region.

The term abdominal cavity has two meanings, one including the pelvic cavity , the other excluding it. Abdominal cavity structure includes both. Abdominal cavity proper excludes the pelvic cavity.

The FMA definition of body organ is also used. Organs include individual bones, joints, muscles, arteries, veins, lymph vessels, nerves, and etc. Concepts that include groups of organs are frequently used in SNOMED CT. In most cases, these have been part of the subsumption hierarchy (IS A hierarchy) of the particular organ type, that is, they are kinds of organs.

For concepts that refer to the collection of organs (rather than organs in a collection), there is another concept that is a, kind of, organ system subdivision. Many such collections do not yet have corresponding organ system subdivision concepts. The default is to interpret concepts as denoting organs, rather than organ system subdivisions.

In general, organs are made up of tissue, and tissue is made up of cells. However, a cell is not necessarily part of tissue, and tissue is not necessarily part of a named organ.

Arteries, veins, nerves, and the bronchi form tree-like structures that distribute across multiple regions. Because of their size and links with other structures, they require slightly different modeling. FMA divides tree structured organs as: organs with organ cavities and organs that are solid.

Organ with organ cavity has a subtype, hollow tree organ. The hollow tree organs are:

• Tracheobronchial

• Biliary

• Vascular

  • Arterial

Among the solid organs, there is one category, neural , that is tree-structured (see: Nervous system; neural tree).

Male and female are unnecessary descriptions in describing the breast. Gender information should be obtained and recorded separately in the information model. New content that requests male or female breast will not be accepted so as not to duplicate gender-specific anatomical concepts.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

The genitourinary system includes the entire urinary system, as well as the genital system. The genital system includes internal genital organs and external genitalia.

Urinary system/tract

The urinary system includes the organs that form and excrete urine, the kidneys, ureters, bladder, and urethra. The male urinary system includes the prostatic urethra (since it is a male urinary outflow structure).

In common usage, urinary system and urinary tract are used interchangeably. However, in SNOMED CT, this is not they case, i.e., they are not synonyms. The two concepts are: 122489005 |Urinary system structure (body structure)| and 431938005 |Structure of urinary tract proper (body structure)|.

Urinary tract proper

The urinary tract proper includes the organs involved in the excretion of urine including the renal pelvis (but not the rest of the kidney), ureters, bladder, and urethra. It is used for disorders affecting the flow of urine (as opposed to its formation) or the urothelium, the lining of the urinary tract.

For example,

• 41368006 |Disorder of urinary tract proper (disorder)|

• 249273002 |Finding of urinary tract proper (finding)|

• 7163005 |Urinary tract obstruction (disorder)|

• 255150000 |Carcinoma in situ of urinary tract proper (disorder)|

The upper urinary tract consists of the kidneys and the ureters (to the juncture with the bladder). Since upper urinary tract infections include kidney infection, the upper urinary tract must include the kidney.

The upper urinary tract proper is the part of the urinary tract proper. It includes only part of the kidney, the renal pelvis, and the ureters.

• For example,

  • 25990002 |Renal pelvis structure (body structure)| has a parent, 431491007 |Structure of upper urinary tract proper (body structure)|.

The lower urinary tract, 19787009 |Lower urinary tract structure (body structure)|, is the urinary system below the junction of the ureter with the bladder. It consists of the bladder and urethra. Lower urinary tract and lower urinary system are the same. The male and female specific components are located under male urinary outflow structure and female urinary outflow structure, respectively.

Obstetric and gravid body structures should not be added inSNOMED CT. Obstetric is a context for a disorder, procedure, or medical specialty that is applied to a body structure during pregnancy, childbirth, or the postpartum period. The context does not change the body structure.

The posterior lobe of the prostate is described in newborns but does not persist in the adult. 113295002 |Structure of lobe of prostate (body structure)| includes three lobes, left and right lateral, and medial.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

The endocrine system is composed of the endocrine pancreas, pineal body, paraganglia, paraaortic bodies, parathyroid glands, endocrine ovaries, endocrine testes, adrenal glands, pituitary gland, thyroid gland, juxtaglomerular apparatus of the kidneys, and some diffuse neuroendocrine structures. Certain parts of the thymus produce endocrine hormones, but the thymus itself is not part of the endocrine system.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

The terms 'spine' and 'vertebral column' in descriptions of conditions or procedures are often used loosely in clinical discourse but can relate to three different general anatomical concepts:

421060004 |Structure of vertebral column (body structure)| (synonym: Spinal column, ‘Backbone’, Spine)

• includes the bones of the spine and associated joints and ligaments

289959001 |Musculoskeletal structure of spine (body structure)|

• includes the vertebral column plus muscles and tendons associated with the spine

1141981001 |Structure of vertebral column region (body structure)|

• includes the musculoskeletal structure of spine plus spinal canal, meninges, spinal cord, roots and ganglia and immediate soft tissue including adjacent vascular structures where specified.

The last concept has been allocated the following definition: This volume includes the spinal column, its spaces and contents, notably the spinal canal, spinal meninges and spinal cord. It also includes the muscles associated with the spine within (and including) the anterior and posterior thoracolumbar fascia and its equivalent nuchal fascia in the neck. This region also includes the spinal ventral (anterior) and dorsal (posterior) roots, the dorsal root (spinal) ganglions and the spinal nerve trunks.

To emphasize the different volumes, cross-sections are shown below of (Figure 1) the vertebral column in yellow, and (Figure 2) the larger vertebral column region in amber color.

From the preceding descriptions, it is clear that Vertebral column region is a broader concept for 'spine', and it should be used when a procedure or condition could involve not only the bony component of the vertebral column, but also the spinal cord, nerve root, muscle, bone, or joint of spine.

For example,

• MRI of thoracic spine (procedure) is modeled with 1141986006 |Structure of thoracic vertebral column region (body structure)|.

• Pain in sacrum (finding) is interpreted as being related to the more general notion of 1144746008 |Structure of sacral vertebral column region (body structure)|.

When a procedure or disorder is exclusively related to musculoskeletal structures of the spine, the 'musculoskeletal structure of spine' should be used.

For example,

• Cervical traction (procedure), Manipulation of the cervical spine (procedure), and Rotational deformity of cervical spine (finding) are all modeled with 297166009 |Structure of musculoskeletal system of cervical spine (body structure)|.

Where a procedure or condition only effects the bone, joint, or ligament component (and not the muscles or tendons directly) the ‘vertebral column variant’ is used for modeling.

For example,

• Benign neoplasm of lumbar vertebral column (disorder) and Kyphoplasty of fracture of lumbar spine using fluoroscopic guidance (procedure) are both modeled with 122496007 |Structure of lumbar vertebral column (body structure)|.

The sacrum is considered equivalent to the sacral vertebral column, as it is composed of the bone structure of the sacrum plus the joint structure of sacrococcygeal junction of spine.

The spine is traditionally divided into the following regions:

• Cervical

• Thoracic

• Lumbar

• Sacral

The anatomy of these individual segments are structured in accordance with the description above.

The regions and joints between these identified segments are referred to as cervicothoracic, thoracolumbar, lumbosacral and sacrococcygeal. The meaning of these words are subject in common parlance and some literature to be ambiguous.

For example,

• ‘Thoracolumbar’ sometimes refers to the thoracic spine and lumbar spine, or alternatively, it is used to express the junction between the thoracic spine and lumbar spine.

To avoid false assumptions, the junction of spinal segments in SNOMED CT have been made explicit by including the word junction in descriptions. This avoids potential misinterpretation as to whether a word such as ‘thoracolumbar' relates to both spinal segments or just the adjacent volume.

For example,

• The notion of 1145014005 |Structure of thoracolumbar junction of vertebral column (body structure)| is only used for modeling when it is explicitly stated in the target concept e.g. 281907005 |Fracture dislocation of thoracolumbar junction (disorder)|.

By contrast, in the circumstance where a dependent concept relates to the combination of two segments, e.g. 702487007 |CT of thoracolumbar spine (procedure), (FSN Computed tomography of thoracic and lumbar spine), the concept is modeled with two axioms, namely Structure of lumbar vertebral column region and Structure of thoracic vertebral column region.

The volume or extent of the junctional zones themselves are not defined consistently in the literature but most commonly relate to the junction between two segments and one vertebra above and below. So the convention used in the SNOMED CT anatomy hierarchy follows this guidance.

For example,

1145014005 |Structure of thoracolumbar junction of vertebral column (body structure)| includes the following concepts in its class:

• 66794005 |Bone structure of L1 (body structure)|

• 23215003 |Bone structure of T12 (body structure)|

• 714833001 |Structure of intervertebral syndesmosis of T12 and L1 (body structure)|

• 181879009 |T12/L1 facet joint (body structure)|

In addition, a further convention is required as to where segmental junctional joints belong, i.e. either to the cephalic or caudal segment. For instance, does the T12/L1 facet joint relate to the Thoracic spine joint structure or/and Lumbar spine joint structure?

The convention used (based on common criteria of spinal injuries) is that the junctional joints are included with the cephalic segment. So, in the case of the T12/L1 facet joint, it is included in the class of Thoracic spine joint structure (body structure).

Similarly, 8454000 |Lumbar spine joint structure (body structure)| subsumes:

• Intervertebral L5-S1 disc

• Structure of lumbosacral joint

• Structure of facet joint between L5 and S1

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

The nervous system has two parts, central and peripheral.

• The central nervous system, sometimes also called the neuraxis , consists of the brain and spinal cord. The pyramidal system is a subdivision of the central nervous system; the extrapyramidal system is part of the brain.

• The peripheral nervous system includes all neural structures outside the central nervous system.

The nervous system is also divided as: autonomic, somatic, and enteric.

• The autonomic system is further divided as sympathetic and parasympathetic. The autonomic system is not entirely a part of the peripheral nervous system, but the autonomic nerves are peripheral.

The word nerve has multiple meanings according to the FMA:

• nerve trunk

• neural organ (trunk plus branches, excluding nuclei, ganglia, and roots)

• neural tree organ, including nuclei, ganglia, roots, etc.

A neural tree organ is defined in FMA as a nonparenchymatous organ which has as its parts an aggregate of neurons (nuclei or ganglia) and their axons which are grouped into fasciculi by connective tissue to form elongated, cable-like structures that are arranged into a tree. A nerve , according to FMA, is defined as a segment of a neural tree organ which has as its parts a nerve trunk and its branches; together with other nerves of the same tree, it constitutes a neural tree. The neural tree structure includes:

• Cranial nerve

  • Complex cranial nerve-tract

• Spinal nerve

• Spinal accessory nerve (strictly neither cranial or spinal nerves)

Nerve , conventionally has two meanings:

• An anatomically distinct nerve trunk (without branches) that is identified in a dissection (e.g. the structure that student identifies when a pin is placed in the trunk of the vagus nerve, for instance located on the arch of the aorta)

• A larger anatomical entity which supports a related set of functions (e.g. all anatomical components of the vagus nerve that are necessary for it to execute its functions (e.g. when a student is asked which nerve is responsible for slowing the heart the answer, the vagus nerve , includes the vagal nucleus, as well as the trunk and branches of the vagus).

• Neural tree designates the second concept in order to distingiush it from the first which is only a part (subdivision of) the vagal neural tree.

A third meaning of nerve, defined by the FMA is: Segment of neural tree organ which has as its parts a nerve trunk and its branches; together with other nerves of the same tree it constitutes a neural tree.

• For example,

  • Chorda tympani, digastric branch of facial nerve, greater petrosal nerve, posterior cutaneous branch of posterior ramus of cervical nerve, superior lateral cutaneous nerve of arm.

  • If one severs the facial nerve, the meaning refers to the trunk. But if one has facial nerve palsy, the meaning refers to the entire distribution of the nerve and the functions served by it.

Cerebrum may refer to the supratentorial brain, which is everything except the midbrain, medulla, pons, and cerebellum. In this interpretation, the telencephalon and diencephalon are in the cerebrum. On the other hand, cerebrum may only refer to the parts derived embryologically from the telencephalon, the cerebral hemispheres and the intercerebral commissure (corpus callosum and anterior commissure).

Supratentorial brain may be used for categorizing tumors and for designating the location of swelling that can result in herniation. The telencephalon and diencephalon (including thalamus, geniculate bodies, pineal body, habenulae, and hypothalamus) are definitely supratentorial. The upper part of the midbrain (mesencephalon) is also supratentorial. SNOMED CT excludes all midbrain structures from the supratentorial brain.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Skin, skin-associated mucosa

This is an example of a body structure that is used to group related terms.

The concept 707861009 |Structure of skin and/or skin-associated mucous membrane (body structure)| intentionally employs disjunction (inclusive Or). It includes structures in the deep layers, but excludes non-skin mucosal epithelium, e.g., bronchial, gastrointestinal, and genitourinary sites of squamous cell neoplasms. The 400199006 |Structure of skin and/or surface epithelium (body structure)| concept is used to represent the sites of these neoplasms.

Skin and/or skin-associated mucosa is intended for use in dermatology. It is not intended to subsume all mucosal structures, which are under Mucous membrane structure (body structure).

Skin regions, skin of <body part>

Since the phrase skin of finger can mean some or all of the skin of finger (if interpreted as a structure, rather than entire in the The StructureEntirePart (SEP) model , we could use IS-A to represent the relationship between skin of finger and skin of hand. Thus, skin of finger IS-A skin of hand, IS-A Skin structure of upper limb, IS-A skin region. The word region is not used in all of these names, because it may refer to the entire region or a part of a region.

Formal definitions of scalp include layers beneath the skin. Therefore we make a distinction between 41695006 |Scalp structure (body structure)| and 43067004 |Skin structure of scalp (body structure)|.

There are at least three different use cases and meanings, and thus categories, for the phrase soft tissue. They include:

• Tumors. Soft tissue gives rise to similar types of neoplasms of mesenchymal stem cell origin, generally called soft tissue neoplasms. This accounts for the inclusions/exclusions of the category. Non-neoplastic masses arising in soft tissue are included in the WHO Classification of Soft Tissue Tumours.

  • For tumors, soft tissue is defined as non-epithelial extraskeletal tissue of the body, exclusive of the mononuclear phagocyte system, glia, and supporting tissue of various mesenchymal organs. Other explicit inclusions are: fibrous tissue, fascia, ligaments, tendons, tendon sheaths, synovia, bursae, skeletal muscle, smooth muscle, fatty tissue, adipose tissue, blood vessels, lymph vessels, peripheral nerves, sympathetic and parasympathetic nerves, and ganglia, as well as subcutaneous tissue. Skin, skeletal cartilage, pleura, and the pericardium, peritoneum, central nervous system, endocrine glands, and viscera are excluded.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Choroid

Both subchoroidal and suprachoroidal refer to the same potential anatomic space between the choroid and the sclera. The term lamina subchoroidea of choroid is the same as the lamina suprachoroidea.

Retinal vein

There is not a vein actually named retinal vein. However, SNOMED CT has concepts with the phrase.

For example,

• 85003000 |Structure of retinal vein (body structure)| has the synonym retinal vein.

  • 280927000 |Entire central vein of the retina (body structure)| has the synonym entire central retinal vein.

371398005 |Eye region structure (body structure)| has a synonym of orbital region structure which subsumes bony orbit, entire eye, and ocular adnexa.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Many terms that refer to body systems or tracts are used imprecisely in clinical practice and in medical publications. Ambiguities frequently arise with many of these terms. We have made the following definitions and distinctions in order to achieve internal consistency of the terminology. We recognize that it may not be possible to get universal consensus for the names for each of these concepts. The goal is to be consistent and clear in defining the meaning of each concept and to allow users and system designers to present the terms that best reflect these meanings in their own implementations.

Pages in this section:

• Body parts and regions

• Cardiovascular System

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Cardiac valves, normal and malformed

There are a number of concepts in the anatomy hierarchy that represent congenital cardiac malformations. This content was developed in cooperation with IPCCC (International Pediatric and Congenital Cardiac Code).

The following pairs of cardiac valve concepts do not represent the same thing and are siblings, not super- or subtypes, to each other:

• 11124005 |Atrioventricular valve (body structure)| vs. 279316009 |Atrioventricular (non-mitral, non-tricuspid) valve structure (body structure)|

• 91134007 |Mitral valve structure (body structure)| vs. 312523009 |Left (non-mitral) atrioventricular valve structure (body structure)|

• 46030003 |Tricuspid valve structure (body structure)| vs. 244344000 |Entire right (non-tricuspid) atrioventricular valve (body structure)|

Atrioventricular (non-mitral, non-tricuspid) valves represent body structures which were anatomically abnormal from the beginning of their development. They are not called mitral/tricuspid valve although they perform the same function as their normal counterpart would. They are also represented using the term not morphologically mitral/tricuspid valve.

• For example,

  • 459176007 |Abscess of right atrioventricular (not morphologically tricuspid) valve (disorder)| represents an abscess of the right atrioventricular valve that has been developed abnormally from the beginning vs. 431189009 |Abscess of tricuspid valve (disorder)|.

For a normally developed mitral/tricuspid valve, the term left/right atrioventricular valve can be used interchangeably. They are true synonyms. However, they cannot be used for abnormally developed valves, i.e. left atrioventricular (non-mitral)/right atrioventricular (non-tricuspid) valves.

The systemic circulatory system is the combined arterial and venous circulation that begins where blood leaves the left ventricle and ends where blood enters the right atrium. It excludes the coronary circulation. The heart chambers are also considered part of the circulatory system.

The pulmonary circulation is the combined arterial and venous circulation that begins where blood leaves the right ventricle and ends where blood enters the left atrium.

Any artery of the pulmonary circulation, i.e. arteries carrying unoxygenated blood from the heart to the lungs. They include the trunk, right and left branches of the pulmonary artery (which are within the mediastinum), and all of their branches (which tend to occur at or past the hilum and are therefore regionally within the lung).

Any artery of the pulmonary circulation that is regionally within the lung, the boundary being defined by the hilum.

The main pulmonary artery (one of the great vessels that enter the heart) carrying blood from the right ventricle and dividing into right and left main pulmonary arteries (some dictionaries consider this synonymous with pulmonary artery).

There are four pulmonary veins that enter the left atrium, two on each side. These are what is intended by the name pulmonary vein (great vessels that enter the heart). In common usage, any vein that is part of the lung may be referred to as a pulmonary vein, but SNOMED CT has a separate concept: 122972007 |Pulmonary venous structure (body structure)|. This means any vein that drains the lung. A synonym is vein of lung. Pulmonary veins are veins of the lung, but pulmonary vein and vein of lung are not synonyms.

The term central vascular is not in common use. In fact, the term does not appear in SNOMED CT. However, the term peripheral vascular is very common, and therefore it requires a definition that (by default) sets the boundary between central and peripheral vascular systems.

The simplest definition of the peripheral vascular system is the vascular system that is not central; and then the central vascular system includes the pulmonary circulation, coronary circulation, cerebrovascular system, thoracic aorta, superior vena cava, inferior vena cava, and mediastinal blood vessels.

Peripheral vascular disease is often distinguished from cerebrovascular disease and coronary artery disease. These are the three major categories of diseases caused by problems in vascular circulation in general, and atherosclerosis, in particular. As a result of this clinical distinction, the cerebrovascular system is excluded from the peripheral vascular system.

Cerebrovascular is commonly defined in two ways: the blood vessels in the brain, or the blood vessels that supply the brain (including those within the brain). Because cerebrovascular disease includes extra-cranial occlusions of the vertebral and carotid arteries, we define the cerebrovascular system as those vessels involved in the supply and drainage of blood to the brain. Convention does, however, tend to exclude the innominate artery - which gives rise to the right common carotid and the arch of the aorta which gives rise to the left common carotid. Convention also excludes the subclavian arteries which give rise to the vertebral arteries.

The common carotid artery has a left and right component. The right common carotid artery has no thoracic portion (it arises from the brachiocephalic trunk behind the right sternoclavicular joint). The left common carotid artery has a thoracic portion (It arises from the arch of the aorta). Thus, the common carotid artery (not specifying laterality) is not exclusively an artery of the neck. This is because of the thoracic portion of the left common carotid artery. Then, artery of neck region includes the cervical part of left common carotid artery and all of the right common carotid artery.

Some vascular trees are located wholly within the cranial cavity, but some (internal carotid; vertebral) cross the boundary between extra- and intra-cranial. Intracranial segments of such vascular trees must be individually identified as such, and the entire vascular tree must not be categorized as either extra- or intra-cranial.

The word artery has three different meanings. In modeling SNOMED CT concepts that refer to arteries, it is necessary to decide on a case-by-case basis which of these meanings is intended.

The word vein has three different meanings. In modeling SNOMED CT concepts that refer to veins, it is necessary to decide on a case-by-case basis which of these meanings is intended.

Because trunks of veins, not venous trees, have been used to organize the vein hierarchy, there are implications for regional classes.

• For example, the internal jugular vein is a vein of the neck, but its entire venous tree extends into the head. The internal jugular vein venous tree is not strictly part of the neck, even though the internal jugular vein venous trunk is strictly part of the neck.

Tributaries are also modeled as direct tributaries of the trunk. A tributary of a named vein is part of the venous tree of the named vein, but not part of the venous trunk of the named vein. Some veins that are part of the venous tree , and therefore might be regarded as indirect tributaries, are not modeled as direct tributaries of the trunk of the vein. Direct tributary is the intended meaning of tributary.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Lymphatic system / 89890002 |Structure of lymphatic system (body structure)|

Set of structures through which lymph flows. It includes 59441001 | Structure of lymph node (body structure) | and 83555006 | Structure of lymphatic vessel (body structure) |. It supports the categorization of findings, disorders and procedures that relate to the flow of lymph.

Lymphoid system / 122490001 |Lymphoid system structure (body structure)|

Set of structures with groups of lymphoid cells, including those in the intestines, marrow, liver, and other locations, and the lymph nodes, spleen, thymus, and tonsils and adenoids; excludes the lymph vessels. It supports categorization of lymphomas.

Immune system / 116003000 |Structure of immune system (body structure)|

All of the lymphoid system, as well as the mononuclear phagocytic system; the immune system also includes cellular and sub-cellular components involved in cellular and humoral immunity.

Mononuclear phagocytic system / 127908000 |Mononuclear phagocyte system structure (body structure)|

Collection of true macrophages, distributed widely in the body (splenic and lymphoid sinusoids, liver Kuppfer cells, pulmonary alveolar macrophages, osteoclasts, macrophages in serous membranes, and microgliocytes); also endothelial cells that line hematopoietic tissues.

Dendritic cell system / 127909008 |Dendritic cell system structure (body structure)|

Collection of antigen-presenting cells, including the following: epidermal Langerhans, dendritic reticulum, and interdigitating. Class I histiocytoses (Langerhans cell histiocytosis) are disorders of the dendritic cell system.

Hematologic system / 414387006 |Structure of hematological system (body structure)|

Bone marrow, the lymphoid system, the hematopoietic system, and the terminal cells of all lineages of the hematopoietic system (red cells, white cells, platelets, histiocytes, plasma cells, etc.). Disorders of the hematologic system do not necessarily include disorders of the hemostatic system, even though bleeding and thrombosis are usually categorized as hematologic.

Structures and cells responsible for erythropoiesis, granulocytopoiesis, monocytopoiesis, thrombocytopoiesis, and lymphopoiesis. Refers to the immature cellular elements that eventually form the cellular components of blood. The blood itself cannot be strictly part of the hematopoietic system, since this would cause all components of blood to be part of the hematopoietic system (including components like albumin, clearly not hematopoietic). SNOMED CT considers leukocytes, erythrocytes, and platelets the result of hematopoiesis, but not blood-forming, otherwise leukocytosis would become a disorder of hematopoiesis, whereas it can arise simply from a demargination of white cells following stress. SNOMED CT has a concept named 419333002 | Cellular component of blood (substance) |; note that platelets are not actually cells, but are cellular components.

The blood is not necessarily part of the cardiovascular system, nor is it necessarily part of the hematopoietic system. 87612001 |Blood (substance)| is a body fluid, not strictly part of either the hematopoietic or cardiovascular systems.

|Lymph node structure| could be a single node or multiple nodes. A term in single form does not mean it is a single anatomical entity. For example, | Inguinal lymph node structure | represents the lymph node(s) in the inguinal region. It is a representation of the type of anatomical entity. A 'Lymph node group' concept could have two distinctive concepts, e.g. lymph node of a particular classification group, or a group of nodes, representing the lymph node according to different groups in most cases. If it represents a group of nodes, the description should be in the plural form.

SNOMED CT has lymph node concepts per their anatomical locations, e.g. pulmonary, bronchopulmonary, tracheobronchial, tracheal, and esophageal) and concepts for node groups used for clinical staging of lung cancer, i.e., lymph nodes categorized into 14 stations.

Professional societies concerned with the clinical staging of lung cancer have developed at least three different nomenclatures for stations of lung-related lymph nodes. Even though the numbering of the stations is very similar, the inter-relationships between the various node groups are complex, particularly in stations 4 and 10, near the carina and hilar regions.

SNOMED International considers American Joint Committee on Cancer (AJCC) Station 10 , hilar lymph node, bronchial lymph node, and bronchopulmonary lymph node as synonyms. The American Thoracic Society (ATS) Station 10R, the right tracheobronchial lymph node is not a subtype of tracheobronchial lymph node because its definition includes nodes covered by both lower paratracheal lymph node,(AJCC Station 4) and by the hilar lymph node (AJCC Station 10). SNOMED CT uses tracheobronchial lymph node as a supertype of both inferior tracheobronchial (subcarinal) and superior tracheobronchial (a subset of lower paratracheal).

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Respiratory tract

321667001 |Respiratory tract structure (body structure)|. In SNOMED CT, respiratory tract has the same meaning as the Nomina Anatomica term apparatus respiratorius , which includes the structures through which air passes from the nares to the alveoli. The oral cavity is not included. In common usage, respiratory system may have the same meaning as respiratory tract ; but not in SNOMED CT. Respiratory system does not mean the global respiratory system that might include the CNS components of breathing. Pleura are part of the lower respiratory system, but not a part of the lower respiratory tract.

Upper aerodigestive tract

This phrase has several meanings. The SNOMED CT concepts 119253004 |Upper aerodigestive tract structure (body structure)| and 361922007 |Entire upper aerodigestive tract (body structure)| have the meaning based on the following reference: Cancers of the upper aerodigestive tract constitute approximately 4% of all malignancies. These include cancer of the lip, tongue, major salivary glands, gums and adjacent oral cavity tissues, floor of the mouth, tonsils, oropharynx, nasopharynx, hypopharynx and other oral regions, nasal cavity, accessory sinuses, middle ear, and larynx (Upper aerodigestive tract cancers, Cancer 1995 Jan 1;75 (1 Suppl): 147-53). This definition matches the tumors included in the CAP Cancer Checklist for upper aerodigestive tumors. The esophagus, or at least the cervical esophagus, may be included, but not in SNOMED CT .

58675001 |Upper respiratory tract structure (body structure)| includes the nasal cavity, paranasal sinuses, nasopharynx, oropharynx, and larynx

82094008 |Lower respiratory tract structure (body structure)| includes the tracheobronchial tree (from the trachea through the terminal bronchioles) and the lungs, including the alveolar respiratory tract (which extends from the respiratory bronchioles to the alveoli).

400141005 |Lower respiratory system structure (body structure)| includes the lower respiratory tract and the pleura.

The interarytenoid fold forms part of the inlet of the larynx. The fold has two surfaces, one forming part of the wall of the supraglottic larynx, the other forming part of the wall of the hypopharynx (the food tube behind the larynx, leading to the esophagus). The 102295003 |Structure of hypopharyngeal aspect of interarytenoid fold (body structure)| may be considered part of the hypopharynx, the larynx, or both. A tumor of this site is categorized as a tumor of the hypopharynx, and not the larynx, but the 105585004 |Interarytenoid fold structure (body structure)| is considered part of the larynx.

SNOMED CT does not give a Part of relationship between the hypopharyngeal aspect of the interarytenoid fold and the interarytenoid fold. This emphasizes SNOMED CT modeling based on the relationship of anatomical entities and disorders and procedures and not simply by reading term names.

SNOMED CT differentiates between the bone underlying the nasal turbinates and the actual turbinates:

Bones underlying the turbinates,

• 118648008 |Inferior nasal turbinate bone structure (body structure)|

• 122491002 |Middle nasal turbinate bone structure (body structure)|

• 122492009 |Superior nasal turbinate bone structure (body structure)|

• 122493004 |Supreme nasal turbinate bone structure (body structure)|

Turbinates, which include bone, overlying mucous membranes, and other tissue,

• 6553002 |Inferior nasal turbinate structure (body structure)|

• 122491002 |Middle nasal turbinate bone structure (body structure)|

• 65289004 |Superior nasal turbinate structure (body structure)|

• 33415007 |Supreme nasal turbinate structure (body structure)|

The 118648008 |Inferior nasal turbinate bone structure (body structure)| is a facial bone and skull bone. And, parts of the ethmoid bone form the middle, superior, and supreme nasal conchae. This means that the bones of the middle, superior, and supreme turbinates are not bone organs.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Skeletal system, bony skeleton

The skeletal system (systema skeletal in Nomina Anatomica) includes bones and cartilage. The bony skeleton includes bones only. The vertebral column is part of the skeletal system and includes the intervertebral discs (fibrocartilage). Individual vertebrae are part of the bony skeleton.

In ordinary usage, bone combines the meanings bone organ and bone tissue.

The 5 anatomical concepts related to bone are:

1. 3138006 |Bone (tissue) structure (body structure)|. Tissue type that makes up bones; a quantity of regular connective tissue consisting of osteocytes and related cells, the intercellular matrix of which is ossified; or any part thereof.

2. 90780006 |Entire bone (organ) (body structure)|. Individual bones, e.g., femur, tibia, ulna, scaphoid, lunate. An organ with cavitated parts; consists primarily of compact (cortical) and cancellous bone surrounding bone marrow cavities; also includes periosteum, endosteum (and, according to FMA, articular cartilage).

3. 118966000 |Skeletal system subdivision (body structure)|. Groups of bones, e.g., spine, skull, bony pelvis.

4. 128530007 |Entire bony skeleton (body structure)|. Pars ossea systematis skeletalis, bone part of the skeletal system.

5. 113192009 |Skeletal system structure (body structure)|. Entire skeletal system, including bones and cartilage.

Bone (tissue) is part of entire bone (organ); entire bone (organ) is part of skeletal system subdivision (system); skeletal system subdivision (system) is part of entire bony skeleton (body structure); and entire bony skeleton (body structure) is part of skeletal system structure (body structure). We can use Entire bone (system) to define aggregate concepts that involve bones.

Bone organs are composed primarily of bone tissue, but there are some non-ossified parts. In particular, periosteum is clearly a part of a bone organ, but is not ossified tissue.

Bone marrow is contained within the marrow cavity, but it is not part of the bone organ. The (empty) marrow cavity is part of the bone organ. The bone marrow structure (body structure) is not a subtype of Bone structure (body structure).

Clinically, marrow disorders are not usually considered bone disorders, nor are marrow procedures considered bone procedures.

For example,

• Bone marrow disorders are not musculoskeletal disorders, but bone disorders are musculoskeletal disorders. Bone marrow transplants are not considered types of bone transplant.

  • 60168000 |Osteomyelitis (disorder)| is not the same as 44462005 |Osteitis (disorder)|.

To differentiate marrow, vessels, nerves, and periosteum from the actual hard tissue of bones, we differentiate structure of tibia from 12611008 |Bone structure of tibia (body structure)|. The bone marrow and other soft tissues of the tibia can then be categorized separately from the hard tissues. Bone marrow diseases are not considered musculoskeletal diseases, so bone marrow structures should not be placed in the bone (tissue) structure hierarchy.

ICD does not use the standard anatomical definition of long bone. For instance, Benign neoplasms of long bones are distinguished from benign neoplasms of short bones ; the bones of the hand are considered short bones. The anatomical definition of long bone cites the proportional relationship between length and width (length >> width). It is clear that metacarpals, metatarsals, and phalanges are included in the anatomical definition of long bone.

In order to accommodate the differences between anatomical definitions and classifications, SNOMED CT has anatomical groupings that correspond to the ICD groupings. Scapula, humerus, radius, or ulna, and long bone of thigh or lower leg are used as the sites for grouper concepts that match ICD definitions and groupings.

The sternum is considered a bone organ. The manubrium, body, and xiphoid are parts of the sternum, classed as zones in the FMA.

Even though teeth are supported by the maxillary or mandibular bone, they are not part of the 70925003 |Bone structure of maxilla (body structure)| or 91609006 |Bone structure of mandible (body structure)|. Teeth are part of the 4335006 |Upper jaw region structure (body structure)| and 48077000 |Lower jaw region structure (body structure)|.

In many diseases and procedures, reference is made to areas of the body that may ambiguously imply either a joint or a region surrounding the joint. Some common ones are:

272691005 | Bone structure of shoulder girdle (body structure)| This concept is used to define diseases and procedures affecting bones in the shoulder region, i.e. proximal humerus, scapula, and clavicle. It is not a bone, but a bone structure, and is part of the shoulder region.

27949001 |Intertarsal joint structure (body structure)|; SYN: Tarsal joint: This structure is part of a group of bones forming the tarsus or tarsal joint (ankle). The 27162001 |Talocalcaneonavicular joint structure (body structure)| is the articulation between the talus (one of the seven bones of the ankle joint) and the other bones of the tarsus, and is what is meant by the rarely-used term talotarsal joint. The talocalcaneal joint is a synonym for the 127863007 |Subtalar joint structure (body structure)|. Dislocations of the subtalar joint usually involve the 127864001 |Structure of talonavicular joint (body structure)|. The subtalar and talonavicular joints constitute the talocalcaneonavicular joint.

The meaning of the words arm and leg may be misinterpreted.

• Arm may refer to the upper limb, but it may also refer to the upper part of the arm.

• Leg may refer to the lower limb, but it may also refer to the lower part of the leg.

• In common usage, leg is a synonym of lower extremity, and arm is a synonym of upper extremity.

In SNOMED CT,

• 53120007 |Upper limb structure (body structure)| includes the shoulder, upper arm, forearm, wrist, and hand

• Upper arm is a synonym to 40983000 |Structure of upper extremity between shoulder and elbow (body structure)|.

• 61685007 |Lower limb structure (body structure)| includes the hip, thigh, lower leg, ankle and foot.

• Lower leg is a synonym to 30021000 |Structure of lower extremity from knee to ankle (body structure)|. Lower leg does not include the foot. Stedman's Medical Terminology

The word limb appears in the FSN of the body structure, while the word extremity appears as a synonym. Therefore, when constructing an FSN for a new clinical finding concept, this precedent should be followed:

• FSN: 61685007 |Lower limb structure (body structure)|

• PT: Lower limb structure

• Synonym: Lower extremity

Additional descriptions of leg and arm are permitted for concepts whose FSNs refer to lower limb and upper limb respectively.

The shoulder region is part of the upper limb, and the hip region is part of the lower limb. This follows the general pattern used in the Foundation Model of Anatomy (FMA).

The FMA defines:

• upper limb as the free upper limb and the pectoral girdle (of which the shoulder region is part). SNOMED CT has the concept 896766000 |Structure of free upper limb (body structure)|.

• lower limb as the free lower limb and pelvic girdle (of which the hip region is part). SNOMED CT has the concept 699617006 |Structure of free lower limb (body structure)|, i.e. the lower limb not including the pelvic girdle.

The axilla is bound by the upper limb laterally and the thorax medially. It may be viewed as not strictly part of the upper limb or the thorax or it may be views as part of both. 91470000 |Axillary region structure (body structure)| is defined in SNOMED CT as being both an upper limb structure and a thoracic structure.

A muscle may be considered an entire functional unit, including attachments to the skeletal system, or merely the contractile part of this unit. In clinical use, muscle is the contractile part only. The FMA definition implies that tendons should be considered part of their corresponding muscles, rather than organs in their own right. SNOMED CT models |Tendon structure| as a subtype of |Skeletal muscle and/or tendon structure (body structure)|. Muscle and tendon are two separate anatomical entities.

• For example,

  • 61352006 |Structure of achilles tendon (body structure)| is not a 53451005 |Triceps surae muscle structure (body structure)| (gastrocnemius and/or soleus) muscle structure.

When modeling muscle categories according to their functions, assume they mean the function of the entire muscle, unless stated otherwise.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

Digestive tract is the same as alimentary tract, and includes the entire passage for food through the body, including mouth, oral cavity (both vestibule of mouth and cavitas oris propria), oropharynx, esophagus, stomach, duodenum, jejunum, ileum, colon, rectum, and anal canal.

Digestive system includes the digestive tract, as well as the associated organs of digestion, including tongue, teeth, salivary glands, liver, exocrine pancreas, gallbladder, and biliary tract.

Gastrointestinal tract has two meanings in common usage. One that does and one that does not include the esophagus. The usage that includes the esophagus would more correctly be named esophago-gastrointestinal tract. Endoscopists frequently use this meaning, even though it is contrary to some dictionary definitions and does not follow strict lexical interpretation (which does not include the esophagus).

Upper gastrointestinal (GI) tract. When describing upper GI bleeding and upper GI radiographic and endoscopic procedures the upper GI tract includes the esophagus, stomach, and duodenum. The upper GI tract does not include the more restricted stomach-intestine entity.

Lower gastrointestinal (GI) tract. When describing lower GI bleeding, lower GI radiographic and endoscopic procedures, and lower GI output from ileostomies and colostomies, the lower GI tract includes the jejunum, ileum, cecum, colon, rectum and anal canal. The ligament of Treitz may be used as the division between upper and lower GI tracts (and the division between the duodenum and jejunum).

Also, since the upper GI tract is said to end at the duodenum-jejunum junction, and there is no concept meaning middle GI tract, the jejunum can be inferred to be in the lower GI tract.

• See J Vasc Interv Radiol 9:747 for an example of inclusion of the jejunum and distal tract as part of the lower GI tract.

The SNOMED CT concepts 119253004 |Upper aerodigestive tract structure (body structure)| and 361922007 |Entire upper aerodigestive tract (body structure)| have the meaning based on the following reference: Cancers of the upper aerodigestive tract constitute approximately 4% of all malignancies. These include cancer of the lip, tongue, major salivary glands, gums and adjacent oral cavity tissues, floor of the mouth, tonsils, oropharynx, nasopharynx, hypopharynx and other oral regions, nasal cavity, accessory sinuses, middle ear, and larynx (Upper aerodigestive tract cancers, Cancer 1995 Jan 1;75 (1 Suppl): 147-53). This definition matches the tumors included in the CAP Cancer Checklist for upper aerodigestive tumors. The esophagus, or at least the cervical esophagus, may be included, but not in SNOMED CT.

Biliary tract includes the gallbladder, intrahepatic and extrahepatic bile ducts, and common bile duct. It does not include the liver. SNOMED CT uses biliary system as a synonym for biliary tract. SNOMED CT has another concept that does include the liver, 732049009 |Entire liver and biliary system (body structure)|.

Mouth has several different meanings including mouth region, oral region of the face, and rima oris.

Mouth region includes structures surrounding the oral cavity, as well as structures of the oral region of the face.

• Use mouth region for most disorders with a finding site of mouth.

Oral region of face includes the skin and subcutaneous tissue of the lips and perioral region, the orbicularis oris muscle, and the vessels and nerves in these structures.

Rima oris is the opening of the mouth.

The four regional parts of the tongue are the ventrum (inferior surface), dorsum, root, and body. The root of the tongue is the posterior third, the dorsal surface of which forms the anterior wall of the oropharynx. The root of the tongue rests on the floor of the mouth. The nerves and vessels that supply the intrinsic muscles of the tongue traverse the root of the tongue.

The terms colorectal and colorectum , commonly used by pathologists, are included in descriptions for concepts referring to neoplasms modeled with 1285733009 |Structure of cecum and/or colon and/or rectum (body structure)|. 1285733009 |Structure of cecum and/or colon and/or rectum (body structure)| is needed because neoplasms are the same from the cecum to rectum and are considered as a group in cancer synoptic reporting protocols. Note, there is no consensus concerning the definition of colon in the literature and between different domains.

This Editorial Guide is used for Education Purposes Only. It is used in the Authoring Courses and Certifications. It is based on the January 2026 Editorial Guide.

The ear includes the external, middle and inner ear. The external ear has two main parts, the auricle (also called the pinna) and the 84301002 |External auditory canal structure (body structure)|.

The external auditory canal has the synonym external auditory meatus. The external auditory meatus is not just the external opening of the canal, but rather the canal extending to the ear drum ( 42859004 |Tympanic membrane structure (body structure)|).

The 61671002 |Structure of internal acoustic meatus of temporal bone (body structure)| (SYN, internal auditory canal, is not part of the ear. As described in the FSN, it is an opening in the temporal bone, and is primarily a nerve conduit that anatomically parallel to the external auditory canal.