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 global standard for correct gross anatomical nomenclature.
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.
Accessory renal arteries are a common variant and are present in ~25% (range 20-30%) and are bilateral in ~10% of the population 7. Their proper identification is of utmost importance for surgical planning prior to live donor transplantation 2,3 and renal artery embolization for various reasons ...
The adrenal glands are supplied by three adrenal (suprarenal) arteries:
superior adrenal artery: arises from ipsilateral inferior phrenic artery
middle adrenal artery: arises from lateral side of abdominal aorta
inferior adrenal artery: arises from the ipsilateral renal artery
The adrenal (suprarenal) glands 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 adrenal gland is usually more pyramidal in...
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 anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge for radiologists and imaging specialists.
Head and neck anatomy
Abdominal and pelvic anatomy
The anterior pararenal space is the portion of the retroperitoneum that lies between the posterior surface of the parietal peritoneum and the anterior reflection of the perirenal fascia.
It contains the duodenum, pancreas and retroperitoneal segments of the ascending and descendi...
The avascular plane of Brodel is the section of renal parenchyma between 2/3 anterior and 1/3 posterior kidney on the cross-section that is relatively avascular. The reason for its relative avascularity is that it represents the plane where the anterior and posterior segmental renal artery branc...
The Bartholin glands, also known as greater vestibular glands, are paired pea-sized structures, lying on either side of the vaginal opening, and are homologous to the bulbourethral (Cowper) glands in the male. They form part of the vulva.
These glands are described as less than 1...
Batson venous plexus, also known as Batson veins, are a network of veins with no valves that connect deep pelvic veins draining the bladder, prostate, and rectum to the internal vertebral venous plexus 1. These veins are important because they are believed to provide a route for spread of pelvic...
A bifid ureter, or ureter fissus, is an example of incomplete duplication of a duplex collecting system.
Present in ~5% (range 1-10%) of the population 1-2.
A bifid ureter is formed when there is a duplex kidney (separate pelvicalyceal collecting systems) drain i...
Bilobed testis, also known as incomplete unilateral polyorchidism, is a very rare variant in children.
The exact etiology is unknown but is thought be a form of incomplete polyorchidism. It has been proposed that bilobed testis results from incomplete division of the urogenital ridge...
Neuroanatomy of the bladder is complex, described here is a summary of the co-ordination of micturition.
The bladder acts as a reservoir normally storing 400-500 mL of urine under low pressure (<15 cmH2O) before voluntary voiding can occur at a socially-convenient time. Bladder filling and empt...
The bulbospongiosus is a muscle found in the superficial perineal pouch which covers the bulb of the penis in males and the bulb of the vestibule in females.
origin: median raphe and perineal body
insertion: dorsum of penis/clitoris, perineal membrane
innervation: pudendal nerve
The bulbourethral glands or Cowper glands are paired small pea-sized glands of the male reproductive tract, analogous to the female Bartholin glands.
The bulbourethral glands are located in the deep perineal pouch posterolateral to the membranous portion of the male urethra and c...
Chromaffin cells are neuroendocrine cells found predominantly in the medulla of the adrenal gland. They are also found in other ganglia of the sympathetic nervous system and are derived from the embryonic neural crest.
They arise in the fifth week of fetal development when neuroblas...
Circumaortic left renal vein, also known as circumaortic renal collar is an anomaly of left renal vein when a supernumerary or accessory left renal vein passes posterior to the aorta, apart from the normal renal vein passing anterior to the aorta. This anomaly is potentially hazardous, if unreco...
Circumcaval ureter, also known as retrocaval ureter, is a term used to describe an abnormal course of a ureter that encircles the inferior vena cava. Both of these terms are somewhat misleading, as this configuration is considered a developmental anomaly of the inferior vena cava (IVC). There ar...
The cloaca is the terminal portion of the hindgut. It is an embryonic structure (weeks 4-7) in which the distal ends of the gastrointestinal tract and urogenital system share a common channel. The most distal aspect of the cloaca is termed the cloacal membrane.
The cloaca, or portions of it, ca...
Congenital urachal anomalies are a spectrum of potential anomalies that can occur due to incomplete involution of the urachus.
A urachal remnant occurs in approximately 1 in 5000 patients.
The urachus connects the dome of the bladder to the umbilical cord during fetal ...
The conjoint tendon forms when the medial fibers of the internal oblique aponeurosis unite with the deeper fibers of the transversus abdominis aponeurosis. The conjoint tendon then turns inferiorly and attaches onto the pubic crest and pecten pubis 1. It forms part of the posterior wall of the i...
The cremasteric artery is a small branch of the inferior epigastric artery that enters the deep inguinal ring of the inguinal canal and supplies the layers of the spermatic cord and also the skin of the scrotum, including the cremaster muscle.
History and etymology
The word "cremaster" derives...
The cremaster muscle is the thin fascial muscle of the spermatic cord made of skeletal muscle. It is also referred to as cremaster fascia or simply the cremaster. Its action is to retract the testes, important in thermoregulation and spermatogenesis.
It is derived from the inter...
Crossed fused renal ectopia refers to an anomaly where the kidneys are fused and located on the same side of the midline.
The estimated incidence is around 1 out of 1000 births 1. There is a recognized male predilection with a 2:1 male to female ratio. More than 90% of crossed ren...
Crossed renal ectopia is said to be present when the kidney is seen in the opposite retroperitoneal space. It is more common for the left kidney to be ectopically located on the right side. More than 85% of these get fused resulting in crossed fused renal ectopia. Less than 15% cases are non-fus...
The dartos muscle is the thin rugated fascial muscle of the scrotum made of smooth muscle. Hence it is also referred to as dartos fascia or simply the dartos. It forms from the subcutaneous tissue of the scrotum and base of the penis and attaches to the scrotal skin and fibrous midline septum be...
The deep inguinal nodes are located within the femoral sheath, medial to the femoral vein. They receive afferent lymphatic drainage from the deep lymphatics of the distal lower extremity and perineum (e.g. glans penis / clitoris), and drain proximally into external iliac lymph nodes via channels...
The deep perineal pouch is an anatomic space superior (deep) to the perineal membrane in the urogenital triangle of the perineum, anterior to the transverse line between the ischial tuberosities.
The deep perineal pouch is above (deep to) the perineal membrane in the urogenital t...
The detrusor muscle (or detrusor urinae muscle)is the smooth muscle component of the urinary bladder and facilitates contraction of the bladder wall during micturition.
Forms the smooth muscle component of the bladder wall. The urothelial lining overlies it within the bladder cav...
Developmental anomalies of the kidneys and ureters are numerous and not only potentially render image interpretation confusing but also, in many instances, make the kidneys more prone to pathology:
horseshoe kidney: most common
cross fused ...
Dorsal nerve of penis or clitoris is one of the two terminal branches of the pudendal nerve that arises from nerve whilst in the pudendal canal. The other terminal branch is the perineal nerve.
Entering the urogenital triangle of the perineum, the dorsal nerve of penis o...
Double retroaortic left renal vein is a very rare entity that is usually clinically silent and detected incidentally at imaging, surgery or autopsy.
The knowledge of anatomical variations helps the surgeon or interventionist to avoid complications during surgery and interventional procedures 4 ...
Dromedary humps are prominent focal bulges on the lateral border of the left kidney. They are normal variants of the renal contour, caused by the splenic impression onto the superolateral left kidney.
Dromedary humps are important because they may mimic a renal mass, and as such is considered a...
The ductus deferens (plural: ductus deferentes) forms part of the male internal genitalia where it transports sperm from the epididymis to the ejaculatory duct. In modern anatomic nomenclature, it is no longer referred to as the vas deferens (plural: vasa deferentia).
The ductus ...
Ectopic kidney, also known as renal ectopia, is a congenital renal anomaly characterized by abnormal location of one or both of the kidneys.
They can occur in several forms:
cross fused renal ectopia
ectopic thoracic kidney
The estimated incidence of an ectopic k...
The ejaculatory ducts are paired structures of the male reproductive system and convey seminal fluid.
Each ejaculatory duct is formed by the union of the excretory duct of the seminal vesicle and the ampulla of the ductus deferens, and is approximately 2 cm long. The ducts course...
A useful mnemonic to remember the ejaculatory pathway of sperm is:
S: seminiferous tubules of the testes
V: vas (ductus) deferens
E: ejaculatory duct
Epididymal appendices, also known as appendix of the epididymis or appendix epididymis, are an testicular appendage found at the head of the epididymis 1. They represent a developmental remnant of the mesonephric duct (Wolffian duct). In 78% of the cases, it has a stalk configuration and is thus...
The epididymis (plural: epididymides) is situated adjacent to the testis within the scrotal sac. Its primary function is the collection, maturation and transport of sperm via the ductus deferens.
The epididymis is an elongated structure, posterolateral to the testis. It can be su...
The external iliac lymph nodes can be found surrounding the external iliac artery and act as the draining nodes for several regions of the pelvis and lower limb.
The external iliac lymph nodes lie anterior to the internal iliac lymph nodes and usually form three separate subgrou...
Extrarenal pelvis refers to the presence of the renal pelvis outside the confines of the renal hilum; it is a normal anatomic variant.
It is found in ~10% of the population 2.
An extrarenal pelvis usually appears dilated, erroneously suggesting...
A faceless kidney refers to one in which the normal appearance of the renal sinus on cross-sectional imaging is absent. It was initially described as a sign of duplication of the collecting system 1 (a slice obtained between the two collecting systems will not demonstrate the normal components o...
The eponym Fallopian may refer to:
Fallopian canal (facial nerve canal)
Fallopian tube (uterine duct)
Fallopian ligament (inguinal ligament)
History and etymology
It is named after Gabriele Falloppio (also known by his Latin name Fallopius), Italian anatomist (1523-1562).
The female urethra is a simple short tube, that transports the urine out of the body, extending from the internal urethral orifice of the bladder to the external urethral orifice in the vestibule of the vagina.
The female urethra measures approximately 4 cm in length. It is embe...
The term fornix (plural: fornices) is used for anatomical structures in multiple organ systems that all share an arch-like morphology:
History and etymology
Fornix is Latin for...
The fossa navicularis refers to a normal mild dilatation of the urethra. It occurs at the most distal/downstream portion of the urethra.
It is more evident in males, where it occurs in the penile/pendulous urethra, near the urethral meatus. There is also a fossa navicularis in women: the more f...
Frenulum (plural: frenula) is an anatomical term and refers to a small fold of soft tissue that checks the movement of an anatomical part.
frenulum (ileocecal valve)
frenulum (labia minora)
History and etymology
Frenulum derives from ...
The gonadal arteries are the paired primary vascular supply to the ovaries in the female and the testes in the male. As the anatomy of the gonadal arteries differs substantially between the sexes, they are covered separately:
The gonadal veins are paired structures that drain the gonads in males and females. In males it is called the testicular vein (or internal spermatic vein) and in females it is called the ovarian vein. The gonadal veins ascend with the gonadal arteries in the abdomen along the psoas muscle anteri...
The great vessel space is the fourth retroperitoneal space along with the anterior and posterior pararenal spaces, and the perirenal space 1,2. Unlike other retroperitoneal spaces, it is not well-defined by fascial planes and thus disease processes affecting other retroperitoneal spaces can also...
A horseshoe adrenal gland is a very rare anomaly. It is also sometimes referred to as a butterfly, fused or midline adrenal gland.
It is a solitary adrenal gland that is present in the midline of the fused portion either passing between the aorta and the inferior vena cava or posterior to the a...
Horseshoe kidneys are the most common type of renal fusion anomaly. They render the kidneys susceptible to trauma and are an independent risk factor for the development of renal calculi and transitional cell carcinoma of the renal pelvis.
Horseshoe kidneys are found in approximate...
The hymen (plural: hymens) is a thin fold of mucous membrane which extends across the vaginal opening, usually with some form of internal defect, which permits the free passage of normal menses.
It usually ruptures during coitus with the remnants, usually in the form of small tags of tissue ar...
Columns of Bertin represent the extension of renal cortical tissue which separates the pyramids, and as such are normal structures. They become of radiographic importance when they are unusually enlarged and may be mistaken for a renal mass (renal pseudotumour).
Nomenclature of such enlarged co...
The hypogastric nerves are paired nerve bundles that are part of the autonomic nervous system and located in the pelvis.
origin: contain sympathetic fibers descending from the superior hypogastric plexus and parasympathetic fibers ascending from the inferior hypogast...
The inferior adrenal (suprarenal) artery is one of three adrenal arteries that supplies the adrenal gland.
Ipsilateral renal artery (usually before the terminal division of the renal artery)
The course of the inferior suprarenal artery depends on its origin. Re...
The inferior hypogastric plexuses are autonomic nerve plexuses located in the pelvis.
location: lies in pelvis in extraperitoneal connective tissue on pelvic sidewall anterolateral to the mesorectum
origin: formed mainly from pelvic splanchnic branches (parasympathetic) and sacral spl...
The inferior rectal nerve, also known as the inferior anal nerve or inferior hemorrhoidal nerve, is a branch of the pudendal nerve which is derived from S2, S3 and S4 nerve roots of the sacral plexus. The nerve provides sensory innervation to the anal canal inferior to the pectinate line and mot...
The inguinal canal is a passage in the anterior abdominal wall that transmits structures from the pelvis to the perineum formed by the fetal migration of the gonad from the abdomen into the labioscrotal folds.
The inguinal canal has an oblique course, is 4 cm in length and has tw...
The internal iliac lymph nodes can be found adjacent to the internal iliac artery and its branches and drain the regions supplied by these vessels. This encompasses a large area from the genitalia anteriorly, the psoas muscle posteriorly and medial thigh inferiorly (see internal iliac artery for...
The internal pudendal veins are the set of accompanying veins to the internal pudendal artery draining the perineal region to empty into the internal iliac vein.
inferior rectal veins
penile bulb and scrotum vein
clitoris and posterior labial vein
An intrathoracic kidney is a very rare form of ectopic kidney. There has been no reported increased incidence of stones or infections as can be seen with other forms of ectopic kidneys. The adrenal glands are usually normal in location.
Intrathoracic kidneys are usually a...
The ischiocavernosus muscles are one of the three main muscles found in the superficial perineal pouch along with the bulbospongiosus and superficial transverse perineal muscle.
origin: ischial tuberosity and ramus
males: corpus cavernosum
Isthmus (plural isthmi) is an anatomical term and refers to a slender structure joining two larger components. Some of these uses of the word isthmus are now rarely used or only seen in older texts and articles:
isthmus (auditory tube)
isthmus (auricle of the ear)
Junctional parenchymal defects in renal imaging are a normal variant.
It results from the incomplete embryonic fusion of renunculi.
It can be seen as a triangular echogenic cortical defect, frequently seen in upper lobe parenchyma. The defect is th...
The kidneys are paired retroperitoneal organs that lie at the level of the T12 to L3 vertebral bodies.
The kidneys are located on the posterior abdominal wall, with one on either side of the vertebral column, in the perirenal space. The long axis of the kidney is parall...
This article lists a series of labeled imaging anatomy cases by system and modality.
CT head: non-contrast axial
CT head: non-contrast coronal
CT head: non-contrast sagittal
CT head: angiogram axial
CT head: angiogram coronal
CT head: angiogram sagittal
CT head: venogram axial
The labia majora (singular: labium majus) form the anteroinferior most part of the vulva, they are continuous with the mons pubis anteriorly and the perineum posteriorly. The labia are apposed in the midline forming the, externally-visible, pudendal cleft.
The labia majora have a...
The labia minora (singular: labium minus) are small glabrous cutaneous folds lying between and just superior to the labia majora. At their posterior margin the labia may be conjoined by a thin cutaneous fold of skin, the frenulum of the labia (also known as the fourchette).
At their anterior m...
The lateral fossae are concave depressions of peritoneum in the paravesical space that lie between the lateral umbilical folds and the lateral parietal peritoneum. The lateral fossae are the smallest of the anterior paravesical fossae, and typically partially contain the cecum and/or sigmoid col...
The lateral umbilical folds are bilateral raised ridges of parietal peritoneum in the deep aspect of the anterior abdominal wall overlying the inferior epigastric vessels. The paired folds originate medial to the deep inguinal ring and end at the arcuate line on the posterior aspect of the anter...
The lateroconal fascia is the peritoneal thickening which extends anterolaterally from the adjoining merging lateral borders of the anterior and posterior perirenal fasciae.
It increases progressively in length as it ranges distally. It traverses laterally in a transverse plane a...
A handy mnemonic to recall the layers of the scrotum is:
Some Damn Englishman Called It The Testes
D: dartos fascia and muscle
E: external spermatic fascia
C: cremasteric fascia
I: internal spermatic fascia
T: tunica vaginalis
T: tunica albuginea
The levator ani, also known as the muscular pelvic diaphragm, is the musculotendinous sheet that forms the majority of the pelvic floor, supports the pelvic viscera, and aids in urinary and fecal evacuation as well as maintaining continence.
The levator ani has three main compone...
The loop-to-loop colon describes an abnormal colonic course associated with the absence of the left kidney from the renal fossa.
The transverse colon extends to the lateral margin of the abdominal wall and the descending colon courses medially to fill the renal fossa, resulting in a "looped" c...
The lying down adrenal sign is a cross-sectional imaging sign of renal agenesis or ectopia in which the ipsilateral adrenal gland appears to be 'lying down' on the psoas muscle posteriorly. Due to the linear as opposed to Y-shaped configuration of the gland in such situations, it is also describ...
The male reproductive system (or tract) includes:
It can be imaged using almost the entire range of imaging modalities but ultrasound and MRI are most often used (in part because...
The male urethra is a fibromuscular tube that drains urine from the bladder. It has a longer, more complicated, course than the female urethra and is also more prone to pathology.
The male urethra measures, on average, 18-20 cm in length. It commences at the internal urethral ori...
A helpful mnemonic to remember the 4 segments of the male urethra from proximal to distal.
Pet My Beautiful Pig
Posterior urethra equates to the prostatic and membranous urethras. Anterior urethra equates to the bulbous and penile ...
The medial fossae are concave depressions of peritoneum in the paravesical space bounded by the medial umbilical folds and the lateral umbilical folds. The fossae are contained within the inguinal (Hesselbach’s) triangle. The right medial fossa typically partially contains the cecum and/or ileum...
The medial umbilical folds are bilateral raised ridges of parietal peritoneum in the deep aspect of the anterior abdominal wall formed by the underlying medial umbilical ligaments running from the pelvis to the umbilicus. The medial umbilical ligaments are anatomical remnants of the obliterated ...
The median umbilical fold is a raised ridge of parietal peritoneum in the deep aspect of the anterior abdominal wall overlying the median umbilical ligament representing the anatomical remnant of the foetal urachus. It is one of the 5 umbilical folds and should not be confused with the bilateral...
Metanephric blastema (or metanephrogenic blastema) is one of the two embryological structure that gives rise to the kidney, the other one being the ureteric bud.
Persistent metanephric blastemas after 36 weeks of gestational age are called nephrogenic rests. They are associat...
The middle adrenal (suprarenal) artery is one of the three adrenal arteries that supply the adrenal gland.
The middle suprarenal arteries arise from the aorta on each side between the inferior phrenic artery and the renal artery. They run laterally across the diaphragmati...
The mons pubis (plural: montes pubis) refers to the rounded protuberant skin-covered soft tissue overlying the symphysis pubis (in both sexes). It is most prominent in adult females.
In females it forms the most superior part of the vulva and it is also called the mons Veneris (plural: montes V...
Musculus compressor nuda is a small striated musculotendinous sling of the bulbocavernosus muscle, which extends from the anterior and lateral surfaces of the proximal bulbous urethra.
Musculus compressor nuda causes the proximal bulbous urethra to form a symmetric convex cone shape where the t...
Nephroptosis, also known as floating/wandering kidney or ren mobilis, refers to the descent of the kidney more than 5 cm or two vertebral bodies when the patient moves from a supine to upright position during IVU 1,2.
Displacement can also occur medially across the midline, so-called medial nep...
The pediatric kidneys follow a growth curve. The measurements below are of the longest maximal dimension. Measurements in parentheses are one standard deviation.
0 months 1: female: 4.15 cm (0.35); male: 4.22 cm (0.32)
2 months: 5.28 cm (0.66)
6 months: 6.15 cm (0.67)
10 months: 6.23 cm (0....
The pampiniform plexus (plural: plexuses) is the venous network of approximately 10 veins draining the testis and epididymis. The network surrounds the testicular artery in the spermatic cord and lies anterior to the ductus deferens. Each network coalesces to form the testicular (internal sperma...
Pancake kidney (also known as discoid kidney, disc kidney, lump kidney, fused pelvic kidney or cake kidney) is a rare renal fusion anomaly of the kidneys of the crossed fused variety.
Pancake kidney may be an incidental finding. However, they can present clinically becaus...
The pararectal spaces are paired, triangular-shaped spaces in the posterior pelvis.
anterior: cardinal ligament
medial: rectal pillars
lateral: levator ani muscle, internal iliac arteries
The pelvic splanchnic nerves also known as nervi erigentes are preganglionic (presynaptic) parasympathetic nerve fibers that arise from S2, S3 and S4 nerve roots of the sacral plexus. These nerves form the parasympathetic portion of the autonomic nervous system in the pelvis.