Abdominal and pelvic anatomy encompasses the anatomy of all structures of the abdominal and pelvic cavities.
This anatomy section promotes the use of the Terminologia Anatomica, the international standard of anatomical nomenclature.
The abdominal aorta (plural: aortas or aortae 4) is the main blood vessel in the abdominal cavity that transmits oxygenated blood from the thoracic cavity to the organs within the abdomen and to the lower limbs.
origin: continuation of descending thoracic aorta at T12
The abdominal cavity is divided into two major compartments, the peritoneum and retroperitoneum, early in fetal development.
The parietal peritoneum is reflected over the peritoneal organs to form a series of supporting peritoneal ligaments, mesenteries and omenta. The peritoneal reflections ca...
Abdominal surface anatomy can be described when viewed from in front of the abdomen in 2 ways:
divided into 9 regions by two vertical and two horizontal imaginary planes
divided into 4 quadrants by single vertical and horizontal imaginary planes
These regions and quadrants are of clinical imp...
The abducens nerve is the sixth cranial nerve. It courses from its nucleus located in the dorsal pons to its innervation of the lateral rectus muscle and can be divided into four parts:
nucleus and intraparenchymal portion
cavernous sinus portion
The abducent or abducens nucleus is a small motor nucleus in the pons for the abducens nerve.
The nucleus is located in the paramedian dorsal lower pons in the floor of the fourth ventricle lateral to the medial longitudinal fasciculus. The nucleus forms a longitudinal paramedian...
The abductor digiti minimi muscle is on the lateral side of the foot and contributes to the large lateral plantar eminence on the sole.
origin: lateral and medial processes of calcaneal tuberosity, and band of connective tissue connecting calcaneus with base of metatarsal V
The abductor digiti minimi muscle overlies the opponens digiti minimi muscle, within the hypothenar eminence, and is one of the intrinsic muscles of the hand. Occasionally an accessory abductor digiti minimi muscle of the hand is present.
origin: pisiform, pisohamate ligament, and tend...
The abductor hallucis muscle forms the medial margin of the foot and contributes to a soft tissue bulge on the medial side of the sole.
origin: medial process of calcaneal tuberosity
insertion: medial side of base of proximal phalanx of great toe
action: abducts and flexes great toe ...
The abductor pollicis brevis muscle is a thin subcutaneous muscle located laterally in the thenar eminence of the hand, and is one of the intrinsic muscles of the hand.
origin: mainly from the flexor retinaculum
few fibers originate from the tubercles of scaphoid and trapezium and ten...
The abductor pollicis longus (APL) muscle is found in the deep layer of the posterior compartment of the forearm. As it descends, it becomes superficial and passes under the extensor retinaculum and through the 1st extensor compartment of the wrist before attaching distally. It is one of the ext...
Aberrant arachnoid granulations, also known as arachnoid pits, are arachnoid granulations that penetrated the dura but failed to migrate normally in the venous sinus. They are most often located in the greater wing of the sphenoid bone and may be seen in idiopathic intracranial hypertension. Occ...
Aberrant internal carotid artery is a variant of the internal carotid artery and represents a collateral pathway resulting from involution of the normal cervical portion (first embryonic segment) of the internal carotid artery 5.
There is consequent enlargement of the usually sma...
Aberrant left pulmonary artery, also known as pulmonary sling, represents an anatomical variant characterized by the left pulmonary artery arising from the right pulmonary artery and passing above the right main bronchus and in between the trachea and esophagus to reach the left lung. It may lea...
Aberrant right subclavian arteries (ARSA), also known as arteria lusoria, are one of the commonest of the aortic arch anomalies.
The estimated incidence is 0.5-2%.
They are often asymptomatic, but around 10% of people may complain of tracheo-esophageal sym...
Abnormal renal rotation (renal malrotation) refers to an anatomical variation in the position of the kidneys, in particular to anomalous orientation of the renal hilum. It may occur unilaterally or bilaterally. It is almost always an asymptomatic incidental finding.
An accessory abductor digiti minimi (ADM) muscle is the commonest accessory muscle of the hypothenar eminence, found in 24% individuals. When present it is one of the intrinsic muscles of the hand.
antebrachial fascia passing anteriorly to Guyon canal
occasionally arises from...
The accessory anterior inferior tibiofibular ligament (accessory AITFL), also known as Bassett's ligament, is an anatomical variant present in many ankles. Pathological thickening of the accessory ligament is seen in the setting of inversion injury that causing the pain due to mild anterior inst...
The accessory appendicular artery, also known as the artery of Seshachalam, is a branch of the posterior cecal artery. It arises from the ileocolic artery, and runs in the mesoappendix.
The exact prevalence of this accessory artery and its impact upon the risk of appendicitis varies among studi...
Accessory breast tissue is a relatively common congenital condition in which abnormal accessory breast tissue is seen in addition to the presence of normal breast tissue. This normal variant can present as a mass anywhere along the course of the embryologic mammary streak (axilla to the inguinal...
Accessory fissures of the lung usually occur at the borders of bronchopulmonary segments. They are common normal variants but are less commonly seen on imaging.
Some of the more common accessory fissure include 1:
azygos fissure: most commonly seen accessory fissure
inferior accessory fissur...
The accessory flexor digitorum longus muscle is an accessory muscle in the deep posterior compartment of the leg with a reported prevalence of 6-8%. Unilateral muscles are more common although bilateral cases have been reported.
origin: variable; either the medial margin of the tibia a...
Accessory gallbladders are a rare anatomical variant occurring in 0.03% of cases (approximately 1 in 3000 people). They can arise from either the left or right hepatic ducts or both. Accessory gallbladders arise from a bifid diverticulum of the hepatic duct in the 5th or 6th week of development ...
The accessory (or superior) hemiazygos vein forms part of the azygos system and along with the hemiazygos vein, it is partially analogous to the right-sided azygos vein. It drains the left superior hemithorax.
Spelling it "hemiazygous" when referring to the vein is incorrect, rega...
An accessory left atrial appendage is a frequent fortuitous finding in cardiac imaging, encountered in ~10% of patients. They are more often seen as a small diverticular structure projecting from the right upper side of the left atrial wall.
it must not be confused with ...
Accessory maxillary ostia are a common anatomic variant, and are usually found incidentally on CT scans of the paranasal sinuses. Accessory ostia of the maxillary sinus are common, occurring in up to 40% patients 1. No significant association has been found between the presence of accessory osti...
The accessory meningeal artery is a branch of the maxillary artery but can also branch from the middle meningeal artery.
The artery passes upwards through the foramen ovale to supply the trigeminal ganglion and the dura mater of Meckel cave and the middle cranial fossa. It also usually supplies...
The accessory middle cerebral artery is a variant of the middle cerebral artery (MCA) that arises from the anterior cerebral artery (ACA). It is different from a duplicated middle cerebral artery, in which the duplicated vessel originates also from the distal end of the internal carotid artery (...
Accessory muscles are a form of anatomic variation that refers to supplementary discrete muscles that are found alongside the normal expected musculature. They have been described in the neck, pelvis, upper and lower limbs.
An accessory navicular is a large accessory ossicle that can be present adjacent to the medial side of the navicular bone. The tibialis posterior tendon often inserts with a broad attachment into the ossicle. Most cases are asymptomatic but in a small proportion it may cause painful tendinosis d...
The accessory ossicle of the anterior arch of the atlas is a normal variant and is best appreciated on a lateral cervical/sagittal study. It is observed as a circular and corticated osseous density that articulates with the inferior aspect of the anterior arch of the atlas.
It is not associate...
Accessory ossicles are secondary ossification centers that remain separate from the adjacent bone. They are usually round or ovoid in shape, occur in typical locations and have well defined smooth cortical margins on all sides.
In most cases, they are congenital in origin, although they may occ...
Accessory ossicles of the feet are common developmental variants with almost 40 having been described. Some of the more common include 1-4:
os tibiale externum (accessory navicular)
os calcaneus secundaris
There are numerous named and unnamed accessory ossicles of the lower limb. These include:
ossicles of the hip
ossicles of the knee
ossicles of the foot
os tibiale externum
os calcaneus secundaris
Accessory ossicles of the wrist are commonly seen on plain radiographs of the wrist and associated cross-sectional imaging. Over 20 were originally described 2, although the more common include 1:
lunula: between TFCC and triquetrum
os styloideum (carpal boss): on dorsal surface of 2nd or 3rd ...
Accessory parotid glands are a normal variant and represent ectopic salivary tissue separate from, but usually in close proximity to, the main parotid glands.
Accessory parotid glands are commonly picked up incidentally on ultrasound; seen in ~20% of the general population 2.
Accessory peroneal muscles are a group of accessory muscles that can occur in the foot region as a normal variant in some individuals. The peroneal compartment is known as the lateral compartment of the leg.
Peroneus quartus muscle
Originally, several accessory muscles were distinguished in th...
The accessory phrenic nerve is an anatomical variant seen in a little over one third of patients (36%). It most commonly arises from the ansa cervicalis, or slightly less commonly, the subclavian nerve. It is unknown as to how much the accessory phrenic nerve contributes to diaphragmatic functio...
Accessory renal arteries are a common variant and are present in ~25% (range 20-30%) and are bilateral in ~10% of the population 1. Their proper identification is of utmost importance for surgical planning prior to live donor transplantation 2,3 and renal artery embolization for various reasons ...
An accessory right inferior hepatic vein is the most common variation of the hepatic veins. It is present in up to 48% of the population and drains the posterior part of the right lobe (mainly segments 6 and 7) directly into the inferior vena cava (IVC).
Variations in hepatic vascular anatomy ...
Accessory sacroiliac joints are a common finding, present on ~15% (range 13-17.5%) of CT studies, and may be unilateral or bilateral. They are an articulation between the medial aspect of the posterior superior iliac spine and the sacrum just lateral to the second dorsal sacral foramen. They may...
The accessory semimembranosus muscle is a rare accessory muscle of the posterior compartment of the thigh. It arises from the distal aspect of the semimembranosus muscle belly and courses through the popliteal fossa between it and the semitendinosus muscle medially and the biceps femoris lateral...
The accessory soleus muscle is an anatomical variant characterized by an additional distinct muscle encountered along a normal soleus muscle. It is uncommon with a prevalence of ~3% (range 0.7-5.5%).
origin: fibula, soleal line of the tibia, or the anterior surface of the soleus muscle...
An accessory superior acetabular notch is a normal variant of the acetabulum, which can be seen on radiographs. It may lead to diagnostic confusion, especially in younger patients.
appear as bilateral symmetric fluid-filled pits in the roof of the acetabulum with sh...
The parietal and occipital bones in particular are common regions for accessory sutures because of their multiple ossification centers.
It is important to know these anatomic variations, mainly on the head trauma image studies in children, where it could be difficult to differentiate non-depres...
The acetabular foramen is formed by the bony margins of the acetabular notch and completed by the transverse ligament of the hip. From its margins (both transverse ligament and acetabular notch) arises the ligamentum teres. Through it pass nutrient vessels to the femoral head epiphysis.
The acetabular fossa, also known as the cotyloid fossa, is the central aspect of the medial wall of the acetabulum that hosts the ligamentum teres and the fibrofatty pulvinar. It is the nonarticular portion inside the U-shaped labrum that extends to the acetabular notch 1. The acetabular fossa i...
Acetabular labrum acts to deepen the acetabulum and increase contact between the pelvis and the femoral head. Its exact biomechanical role remains to be fully elucidated.
The acetabular labrum is a C-shaped fibrocartilaginous structure with an opening anteroinferiorly at the site...
The acetabular notch is a depression in the margin of the acetabulum located anteroinferiorly. It is bridged by the transverse ligament, and thus forms the acetabular foramen. The ligamentum teres has part of its origin from the acetabular notch.
The acetabulum (plural: acetabula) is the large cup-shaped cavity on the anterolateral aspect of the pelvis that articulates with the femoral head to form the hip joint.
All three bones of the pelvis (the ilium, ischium, and pubis) together form the acetabulum. The three bones ar...
The shape of the acromion had been initially divided into three types (which was known as the Bigliani classification) 3, to which a fourth has been added 2. They are used as a standardized way of describing the acromion, as well as predicting to a degree the incidence of impingement.
The acromioclavicular joint (ACJ) is a planar diarthrodial synovial joint of the pectoral girdle.
The acromioclavicular joint is between the small facet of the convex distal clavicle and flat anteromedial acromion. The articular surfaces are lined with fibrocartilage (like the st...
There is much variation in acromioclavicular joint configuration, which may be confused with pathology. The relationship of the acromion to the distal clavicle at the AC joint can be described in the coronal plane as 1-3:
low-lying: associated with shoulder impingement (unfo...
The acromion (plural: acromia), also known as the acromial process, is a small projection of the scapula that extends anteriorly from the spine of the scapula.
It forms the acromioclavicular joint (ACJ) with the lateral third of the clavicle and also connects with the coracoid p...
The adductor brevis muscle is a muscle in the medial compartment of the thigh that lies immediately deep to the pectineus and adductor longus.
origin: external surface of body of pubis and inferior pubic ramus
insertion: pectineal line and proximal part of linea aspera of femur
The adductor canal (also known as the Hunter canal or subsartorial canal) is a muscular tunnel in the thigh. It commences at the inferior end of the femoral triangle and terminates at the adductor hiatus.
from apex of the femoral triangle to the adductor hiatus
The adductor hallucis muscle arises by two heads, an oblique and transverse head. It is responsible for adducting the big toe.
transverse head: ligaments associated with metatarsophalangeal joints of lateral three toes
oblique head: bases of metatarsals II to IV and from sheat...
The adductor longus muscle is a muscle in the medial compartment of the thigh that lies anterior to the adductor magnus muscle.
origin: external surface of body of pubis (triangular depression inferior to pubic crest and lateral to pubic symphysis)
insertion: linea aspera on middle o...
The adductor magnus muscle is the largest and deepest of the muscles in the medial compartment of the thigh. Like the adductor longus and brevis muscles, the adductor magnus is a triangular or fan-shaped muscle anchored by its apex to the pelvis and attached by its expanded base to the femur.
The adductor minimus muscle is a small, variably present muscle in the medial compartment of the thigh.
Due to confusion about this muscle over the years it has ended up with a variety of names, which include pars lateralis, adductor quartus muscle, premier faisceau du grand addu...
The adductor pollicis muscle is a large triangular muscle anterior to the plane of the interossei that crosses the palm of the hand. It is deep to the thenar eminence, forming part of the short muscles of the thumb, and the intrinsic muscles of the hand.
transverse head: 3rd m...
The adductor tubercle is a bony protuberance on the medial condyle of the femur and is located superior to the medial epicondyle. It demarcates the inferior most aspect of the medial supracondylar line. The adductor tubercle is the point of insertion for the adductor minimus and the hamstrings p...
The adenoid tonsils, or often just simply the adenoids (also known as the nasopharyngeal or pharyngeal tonsils), are paired foci of lymphatic tissue located on the superoposterior wall of the nasopharynx and form part of Waldeyer's ring.
Adnexa (single/plural) is a general term that refers to the accessory structures of an organ.
Adnexa have been described in relation to:
hair follicles, sweat glands, nails
structures in the mastoid (posterior) wall of the middle ear, e.g. mastoid antr...
The adnexa, or more formally the adnexa uteri, and also known as the uterine appendages, is a collective term for the:
Some texts also include the associated blood vessels, nerves and other supporting tissues in the definition. It is interesting to not...
The adrenal glands are highly vascular. Threefold arterial supply includes the:
superior adrenal arteries: typically 6-8 in number, arising from the ipsilateral inferior phrenic artery
middle adrenal artery: one or more, arising from lateral side of abdominal aorta
inferior adrenal artery: o...
The adrenal (suprarenal) glands (often shortened to just the adrenals) are paired organs of the endocrine system, often asymmetric in shape.
Each gland is enclosed in the perirenal fascia and each has a body and two limbs: a medial limb and a lateral limb. However, the right adr...
The venous drainage of the adrenal (suprarenal) glands is typically comprised of a single vein draining each adrenal gland. Like the gonadal veins each side drains differently:
left suprarenal vein drains into the left renal vein 1.
right suprarenal vein drains directly into the inferior vena ...
Adventitial bursae are those bursae that develop later in life in response to pressures developed as a result of acquired bony prominences or deformities 1. These bursa can become inflamed resulting in adventitious bursitis.
The biological/medical term agenesis (plural: ageneses) refers to failure of an organ to grow or develop during the embryological period.
corpus callosum agenesis
dental agenesis (anodontia)
Agenesis of the appendix is extremely rare, with an incidence at surgery of approximately 1 in 100,000 laparotomies 1. It is most commonly due to a sporadic etiology. However in the rare genetic condition, familial apple peel jejunal atresia, absence of the appendix is a recognized feature. Also...
Agenesis of the left hepatic lobe is a rare variation in liver anatomy. It is clinically asymptomatic and discovered during imaging or surgery.
absence of the left hepatic lobe (left of the falciform ligament, Couinaud segments 2 and 3)
absence of left hepatic artery, le...
Agenesis of the right hepatic lobe is a rare variation in liver anatomy.
absence of the right hepatic lobe
absence of right hepatic artery, right portal vein, and right hepatic biliary system
compensatory hypertrophy of the left hepatic lobe and caudate lobe
Agger nasi air cells are the most anterior ethmoidal air cells lying anterolateral and inferior to the frontal recess and anterior and above the attachment of the middle turbinate. They are located within the lacrimal bone and therefore have as lateral relations the orbit, the lacrimal sac and t...
AICA-PICA dominance refers to the principle that the cerebellar vascular territory supplied by the anterior inferior cerebellar artery and posterior inferior cerebellar artery have a reciprocal arrangement. That is the size of the AICA and the subsequent territory it supplies is inversely propor...
The alar fascia is a thin fibroareolar membrane separating the (anterior) true retropharyngeal space from the (posterior) danger space. It is the ventral component of the deep layer of the deep cervical fascia.
Notably, in the well patient, the alar fascia is not usually visible on cross-sectio...
The alar ligaments join the lateral margins of the sloping upper posterior margin of the dens of C2 to the lateral margins of the foramen magnum (adjacent to the occipital condyles) and lie on either side of the apical ligament. They may be oblique or vertical and are thickest at the occipital a...
The alar thoracic artery is a rare variant arterial glandular branch of the axillary artery (usually the second part) that supplies the axillary fat, lymph nodes and skin of the axilla.
The alveoli (singular: alveolus) are tiny hollow air sacs that comprise the basic unit of respiration.
Alveoli are found within the lung parenchyma and are found at the terminal ends of the respiratory tree, clustered around alveolar sacs and alveolar ducts. Each alveolus is app...
Amastia is a rare congenital condition characterized by the absence of breast tissue, nipple and areola. This may occur unilaterally or bilaterally.
During embryological development, breasts first appear as ectoderm ridges during the 6th week of gestation. This ridge grows thicker an...
Amazia is a rare congenital condition defined by the absence of glandular parenchyma in either one or both of the breasts and a normal nipple and areola complex.
This is a very rare entity and the true prevalence is not known. Although there are strict definition criteria, the di...
The ambient cistern is part of the subarachnoid cisterns, filled with CSF.
The ambient cistern is a thin, sheet-like extension of the quadrigeminal cistern that extends laterally around the midbrain and posterior to the thalami. It acts as the connection between the quadrigeminal...
Amnion refers to a membranous structure which covers and protects the embryo. It forms inside the chorion. The amnion usually fuses with the outer chorion by around 14 weeks of gestation.
The amnion can be visualized in most pregnancies before the 12th week of...
Amphiarthroses are a functional class of joint that permit a small amount of movement under normal conditions.
symphyses (secondary cartilaginous joints)
Ampulla (plural: ampullae) is an anatomical term used for tubular structures with a short segmental bulbous dilatation:
ampulla (fallopian tube)
ampulla (lacrimal system)
ampulla (semicircular ducts)
ampulla of Vater
ampulla (vas defe...
The ampulla of Vater is a conical structure at the confluence of the common bile duct (CBD) and the main pancreatic duct that protrudes at the major duodenal papilla into the medial aspect of the descending duodenum. The entire structure is encased by smooth muscle fibers that compose the sphinc...
The amygdala (plural: amygdalae) is a very well studied part of the limbic system and forms part of the mesial temporal lobe.
The amygdala is a complex grey matter structure located anterior and superior to the temporal horn of the lateral ventricle and head of the hippocampus. ...
The anal canal is the terminal part of the gastrointestinal tract, whilst the anus (plural: anuses or ani) specifically refers to the opening separating the anal canal from the outside, at the distal most aspect of the anal verge. Anatomically, the anal canal is referred to as the terminal alime...
Anal margin or perianal skin is arbitrarily defined as a skin tissue with a radius of 5 cm from the anal verge, consisting of keratinizing squamous epithelial tissue containing hair follicles. A radius of 5 cm approximately equates to a circle of area of 78.5 cm2 centered on the anal verge.
The anal sphincter is divided into internal and external anal sphincters. It surrounds the anal canal.
Internal anal sphincter
continuation of inner rectal muscle
thickened, circular muscle fibers, up to 5 mm thick
composed of visceral muscle
External anal sphincter
The anal triangle forms the posterior half of the diamond-shaped perineum. The triangle's three corners are defined by the tip of the coccyx posteriorly and both ischial tuberosities anterolaterally. The anterior border is the transverse perineal muscles and the posterolateral borders are the sa...
The anal verge is part of the anal region and consists of a band of squamous epithelial tissue which lacks hair follicles and extends from the inter-sphincteric groove to the perianal skin.
Multiple, highly-variable anastamoses exist between the internal and external carotid arteries. These anastamoses may not be evident on non-invasive imaging or even catheter angiography, and may only be demonstrable with elevated intra-arterial pressures or high-flow states. ICA-ECA collaterals ...