Boundaries and walls
The space has a triangular shape, with its apex pointing superiorly and its base inferiorly.
Fossa boundaries:
- Anteriorly: superficial transverse perineal muscle (m. transversus perinei superficialis).
- Posteriorly: inferior edge of the gluteus maximus muscle (m. gluteus maximus).
- Medially: external anal sphincter (m. sphincter ani externus).
- Laterally: ischial tuberosity (tuber ischii).
Walls:
- Lateral wall is formed by the lower two-thirds of the obturator internus muscle (m. obturatorius internus). It is covered by the parietal pelvic fascia. It is here, within the fascial splitting, that the pudendal canal (canalis pudendalis, or Alcock's canal) is formed.
- Medial wall is represented by the inferior surface of the levator ani muscle (m. levator ani), which is covered by the inferior fascia of the pelvic diaphragm (fascia diaphragmatis pelvis inferior). This muscle descends obliquely from top to bottom and from outside to inside, forming an inferiorly opening angle with the lateral wall.
Apex of the fossa is located at the site where the fascia of the obturator internus muscle fuses with the fasciae of the pelvic diaphragm—this is the tendinous arch of the pelvic fascia (arcus tendineus fasciae pelvis).
Recesses and contents
The cavity of the fossa is filled with the fat body of the ischiorectal fossa (corpus adiposum fossae ischiorectalis), which performs a shock-absorbing function. Two important recesses are distinguished within the space:
- Pubic recess (recessus pubicus) extends anteriorly, lying directly beneath the posterior edge of the urogenital diaphragm.
- Gluteal recess (recessus glutealis) is directed posteriorly, extending beneath the edge of the gluteus maximus muscle. Topographically, this recess corresponds to the inferior part of the deep cellular space of the gluteal region.
Topography of vessels and nerves
The key structure of the lateral wall is the internal pudendal neurovascular bundle. It emerges from the gluteal region through the lesser sciatic foramen and enters the pudendal canal. The branches of the internal pudendal artery and pudendal nerve supply blood and innervation to the perineal skin, scrotum (or labia majora), and penis (or clitoris).
The inferior rectal vessels and nerves (a. et v. rectales inferiores, nn. rectales inferiores) branch off from the main bundle. They pierce the obturator fascia just inferior to the posterior sacrospinous ligament and run toward the anus strictly in the frontal plane. Surgeons must crucially take this branch orientation into account when draining purulent collections to avoid iatrogenic injuries.
Topographical relationships in a pelvic section
The layered structure of this region is clearly visualized on an oblique-transverse pelvic section. The peritoneum (peritoneum) lines the pelvic cavity superiorly. Internal organs are located beneath it: the urinary bladder (vesica urinaria), urethra (urethra), vagina (vagina) in females, and rectum (rectum).
The ischiorectal fossa is located inferior to the pelvic diaphragm. The fat body of the fossa is clearly visible on the section, bounded superiorly and medially by the levator ani muscle, and laterally by the obturator internus muscle. Fascial layers, such as the superior and inferior fasciae of the pelvic diaphragm (fascia diaphragmatis pelvis superior et inferior), form a robust framework separating the fossa adipose tissue from the lesser pelvis organs.
Clinical significance
The abundant adipose tissue of the fossa provides a favorable environment for infection. Abscesses develop precisely here in cases of paraproctitis. Furthermore, surgeons use the ischiorectal fossa as an access pathway to drain phlegmon located in the subperitoneal cellular spaces of the lesser pelvis.
For local anesthesia (pudendal nerve block), a clear bony landmark is used: the injection is made 4–5 cm superior to the inferior edge of the ischial tuberosity.
Briefly: answers to topical questions
Which specific vessels and nerves (with a full enumeration) make up the pudendal neurovascular bundle in Alcock's canal?
The pudendal neurovascular bundle passing through Alcock's canal (pudendal canal) includes:
- internal pudendal artery (a. pudenda interna);
- internal pudendal vein (v. pudenda interna);
- pudendal nerve (n. pudendus).
Through what pathways can purulent collections spread from the ischiorectal fossa (connections of the cellular space)?
Purulent collections from the ischiorectal fossa can spread into the gluteal region. Connection with the gluteal region occurs through the lesser sciatic foramen. Additionally, the fossa serves as a pathway for draining phlegmon of the subperitoneal cellular spaces of the lesser pelvis.
To easily memorize the walls of the fossa, imagine a tent: the lateral wall (obturator muscle) stands almost vertically, while the medial wall (levator) descends toward it at an angle, like a roof slope. The apex of the "tent" is the tendinous arch.
Class and exam questions
Where does Alcock's canal run and what does it contain?
The pudendal canal (Alcock's canal) is located on the lateral wall of the fossa within the splitting of the obturator fascia. The pudendal neurovascular bundle runs through it.
In which plane do the inferior rectal vessels and nerves run?
They run toward the anus strictly in the frontal plane. This is a critical landmark in the surgical treatment of paraproctitis.
With which regions do the recesses of the ischiorectal fossa communicate?
The gluteal recess is topographically connected to the deep cellular space of the gluteal region, whereas the pubic recess extends beneath the urogenital diaphragm.
What else to study on this topic
- Topography of the pudendal canal (Alcock's canal) and its walls
- Connection of the gluteal recess with the cellular tissue of the gluteal region
- Technique for performing a pudendal nerve block
- Surgical anatomy of surgical approaches in paraproctitis
- Pelvic fasciae: parietal and visceral layers
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