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%) of the population. Their proper identification is of utmost importance for surgical planning prior to live donor transplantation 3,4 and renal artery embolisation for various reasons 5.
The term extra renal art...
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 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...
Batson venous plexus (or Batson veins) is 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 cancer meta...
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 aetiology 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 ridg...
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...
A circumcaval ureter, or retrocaval ureter, is a developmental anomaly of the inferior vena cava (IVC). Unfortunately both terms suggest that the ureter is at fault, whereas in reality it is the IVC. They are of two types:
Many patients with this anom...
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 fibres of the internal oblique aponeurosis unite with the deeper fibres 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 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...
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.
Crossed fused renal ectopia essentially 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 recognised male predilection with a 2:1 male to female ratio. More than 90% of...
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 perineal pouch is an anatomic space above the perineal membrane in the urogenital triangle of the perineum, posterior to the transverse line between the ischial tuberosities.
The deep perineal pouch is above (deep to) the perineal membrane in the urogenital triangle.
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.
The ductus deferens is a paired 30-45...
Ectopic kidney (or renal ectopia) is a developmental renal anomaly characterised by abnormal anatomical 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 ectopi...
An ectopic ureter is a congenital renal anomaly that occurs as a result of abnormal caudal migration of the ureteral bud during its insertion to the urinary bladder. Normally the ureter drains via the internal ureteral orifice at the trigone of the urinary bladder.
In females, the most common ...
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. They course throu...
A useful mnemonic to remember the ejaculatory pathway of sperm is:
S: seminiferous tubules
V: vas (ductus) deferens
E: ejaculatory duct
An epididymal appendix (or alternatively appendix of the epididymis or appendix epididymis) is a testicular appendage that is a developmental remnant of the mesonephric duct (Wolffian duct) which can be found in the head of the epididymis 1. In 78% of the cases, it is stalked and is thus easily ...
The epididymis (plural: epididymides) is situated adjacent to the testes 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 testes, with head, body ...
Extrarenal pelvis refers to the presence of the renal pelvis outside the confines of the renal hilum. It is a normal variant that is found in ~10% of the population 2.
The renal pelvis is formed by all the major calyces. An extarenal pelvis usually appears dilated giving a false indication of ...
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 female urethra is a simple tube that extends 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 embedded in the anterior vaginal wall and runs with...
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...
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 and in females it is called the ovarian vein. The gonadal veins ascend with the gonadal arteries in the abdomen along the psoas muscle anterior to the ureters. Like the s...
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 process affecting other retroperitoneal spaces can also ...
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...
A column of Bertin is 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 columns ...
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 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...
An intrathoracic kidney is a very rare form of ectopic kidney. There has been no reported increased incidence of stones or infections as with other forms of ectopic kidneys. The adrenal glands are usually normal in location.
Intrathoracic kidneys are usually asymptomatic ...
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...
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 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 anterior abdomi...
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 faecal evacuation as well as maintaining continence.
The levator ani has three main compon...
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 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 these modalities are n...
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 Big Penis
Posterior urethra equates to the prostatic and membranous urethras. Anterior urethra equates to the bulbous and penile urethras.
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 raised ridges of parietal peritoneum in the deep aspect of the anterior abdominal wall formed by the underlying medial umbilical ligaments. The paired folds run from pelvis to umbilicus. The medial umbilical ligaments are anatomical remnants of foetal umbilical art...
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. It runs from the apex of the bladder to the umbilicus. The median umbilical ligament is the anatomical remnant of the foetal urachus. The ...
Metanephric blastema (or metanephrogenic blastema) is one of the two embryological structure that give rise to the kidney, the other one being the ureteric bud.
Persistent metanephric blastema after 36 weeks of gestational age are called nephrogenic rests. They are associate...
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...
Nephroptosis, also known as floating or wandering kidney and 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...
The paediatric 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 is the venous network of approximately 10 veins draining the testes 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 veins.
Along with the cremaster an...
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 fibres 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.
The paravesical spaces are paired avascular spaces of the pelvis. The paravesical spaces generally contain fat, but can become filled with ascites, blood, or other substances during pathological processes.
superior: lateral umbilical folds
inferior: pubocervical fasc...
Pelvic kidney (sometimes known as sacral kidney) is a kidney that is fixed in the bony pelvis or across the spine 1.
Pelvic ectopia is seen in 1 in 2100-3000 autopsies. It is considered the most common form of renal ectopia 4.
These patients are asymptomati...
The pelvic peritoneal space is the inferior reflection of the peritoneum over the fundus of the urinary bladder and the front of the rectum at the junction of its middle and lower thirds. In females, the reflection is also over the anterior and posterior surface of the uterus and the upper poste...
The penis is the most distal part of the male urogenital system.
The gross anatomy of the penis can be broken into five sections:
loosely connected to the tunica albuginea
distally folded to form the prepuce (foreskin) at the corona of the penis
the internal layer of th...
The perineal nerve or the perineal branch of the pudendal nerve is the largest terminal branch of the pudendal nerve which is derived from S2, S3 and S4 nerve roots of the sacral plexus. The perineal nerve gives muscular branches to superficial and deep perineal muscles as well as the external ...
The perineum is a diamond shaped region below the pelvic diaphragm and is divided by an imaginary line drawn between the ischial tuberosities into anteriorly the urogenital triangle and posteriorly the anal triangle.
The perineum is bounded by the pubis anteriorly, the ischial tu...
The perirenal fascia is a dense, elastic connective tissue sheath that envelops each kidney and adrenal gland together with a layer of surrounding perirenal fat.
It is a multi-laminated structure which is fused posteromedially with the muscular fasciae of the psoas and quadratus lumborum muscle...
The perirenal space is the largest of the three divisions of the retroperitoneum and is the most easily identified. It contains the kidneys, renal vessels and proximal collecting systems, adrenal glands and an adequate amount of fat to allow identification on CT scanning.
The space is surrounde...
Persistent fetal lobulation is a normal variant seen occasionally in adult kidneys. It occurs when there is incomplete fusion of the developing renal lobules. Embryologically, the kidneys originate as distinct lobules that fuse as they develop and grow.
It is often seen on ultrasound, CT or MRI...
Polyorchidism (or supranumerary testes) refers to the presence of more than two testes and is a very rare congenital anomaly. The supernumerary testis can be usually located inside the scrotum (75% of the patients) or less commonly in the inguinal canal, the retroperitoneum, or the abdominal cav...
The posterior pararenal space is the smallest and most clinically insignificant portion of the retroperitoneum.
It is filled with fat, blood vessels and lymphatics, but contains no major organs.
posteriorly: bound by transversalis fascia
anteriorly: bound by posteri...
The prostate gland is part of the male reproductive system and is the largest male accessory gland. It typically weighs between 20-40 grams with an average size of 3 x 4 x 2 cm. The prostate is comprised of 70% glandular tissue and 30% fibromuscular or stromal tissue 1-3 and provides approximate...
The rectouterine pouch, also known as the rectovaginal pouch, cul-de-sac or pouch of Douglas, is an extension of peritoneum between the posterior wall of uterus and the rectum in females. It is the most dependent part of the peritoneal cavity and is analogous to the rectovesical pouch in males.
Rectovesical pouch is the forward reflection of the peritoneum from the lower third of the rectum to the upper part of the bladder in males.
The rectovesical pouch is the lowest part of the peritoneal cavity and usually contains loops of small bowel or sigmoid colon. It is 7.5 cm...
Renal agenesis refers to a congenital absence of one or both kidneys. If bilateral (traditionally known as the classic Potter syndrome) the condition is fatal, whereas if unilateral, patients can have a normal life expectancy.
Unilateral renal agenesis affects approximately 1 in ...
The renal arteries originate from the abdominal aorta and enter the renal hila to supply the kidneys. Any variant in arterial supply is important to clinicians undertaking surgery or other interventional renal procedures.
Arises from the abdominal aorta at the L1-2 vert...
A renal hilar lip is a developmental anomaly of the kidney. It is an infolding of the cortex at the level of the renal sinus and in this region the renal cortex appears thicker.
On imaging it appears as supra- or infra-hilar cortical bulges. At certain levels of cross ...
The renal pelvis forms part of the pelvicalyceal system of the kidney and is the connection between the calyces and the ureter.
The renal pelvis is triangular in shape, lies posteriorly in the renal hilum surrounded by fat and vessels and is formed by the either the union of two-...
The renal sinus is a fat-filled compartment of the kidney.
The renal sinus is a fatty compartment located within the medial aspect of the kidney. It communicates with the perinephric space. It contains the renal hilum and is bordered by renal parenchyma laterally.
The renal veins are asymmetric paired veins that drain the kidneys.
The renal vein is formed by the union of two-to-three renal parenchymal veins in the renal sinus. It emerges from the renal hilum anterior to the renal artery and drains into the inferior vena cava at th...
There are several variations in renal venous anatomy. Some of these are specific to the left renal vein.
Left renal vein anomalies are generally classified into four types 2:
ventral pre-aortic limb of the left renal vein is obliterated, but the dorsal retro-aortic limb persists and j...
Retroaortic left renal vein (RLRV) is an anatomical variant where the left renal vein is located between the aorta and the vertebra and drains into the inferior vena cava.
Its recognition is important in order to avoid complications during retroperitoneal surgery or interventional procedures 2....
The retropubic space (also known as the prevesical space or cave of Retzius) is an extraperitoneal space located posterior to the pubic symphysis and anterior to the urinary bladder. It is separated from the anterior abdominal wall by the transversalis fascia and extends to the level of the umbi...
The scrotum is a dual-chambered protuberance of skin and muscle that contains the testes, epididymides, and spermatic cord. It consists of two chambers separated by a septum It is an extension of the perineum, and is located between the penis and anus.
The scrotal wall is compos...
The seminal vesicles are paired accessory sex glands of the male reproductive system. The seminal vesicle produces over two-thirds of the ejaculate and is very high in fructose.
The seminal vesicle is actually a 10-15 cm long tubular structure but is coiled tightly so it only me...
A sigmoid kidney is an uncommon variant of the horseshoe kidney. Whereas the typical horseshoe kidney is fused only at the lower poles, in a sigmoid kidney both the upper and the lower poles are fused 1.