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AN51.1-2 | Sectional Anatomy — Part 2

Part 4: Midsagittal Section of the Male Pelvis (AN51.2)

Male Pelvic Midsagittal Section — Structures From Anterior to Posterior

The midsagittal (median sagittal) section divides the pelvis into right and left halves. On the midsagittal section, the following structures are seen in the midline from anterior to posterior:

Anterior:
• Pubic symphysis — cartilaginous joint anteriorly; gives origin to muscles
• Retropubic (cave of Retzius) space — extraperitoneal fat between pubis and bladder
• Urinary bladder — lies directly posterior to the pubic symphysis; its apex has the median umbilical ligament (obliterated urachus) attaching to the umbilicus
• Peritoneum — covers the superior surface of the bladder; reflects posteriorly as the rectovesical pouch (the most dependent peritoneal recess in the male pelvis)

Middle structures:
• Seminal vesicles — posterior to the bladder base, above the prostate
• Prostate gland — lies between the bladder neck (above) and urogenital diaphragm (below); the prostatic urethra passes through it
• Ejaculatory ducts — formed by union of vas deferens and seminal vesicle ducts; open into the prostatic urethra at the seminal colliculus (verumontanum)

Posterior:
• Rectum — S3 to the anorectal junction; the rectovesical pouch separates the bladder from the rectum superiorly; the fascia of Denonvilliers (rectovesical fascia) separates them inferiorly
• Sacrum and coccyx — form the posterior wall; the concavity of the sacrum allows the sigmoid colon and rectum to occupy the pelvic floor

Floor:
• Levator ani muscle — the funnel-shaped pelvic diaphragm; separates the pelvis from the perineum
• Anal canal — passes through the pelvic floor at an angle (anorectal angle 90°, maintained by the puborectalis sling)

Clinical relevance:
• Prostate cancer (most common cancer in men over 60 in India): MRI of the pelvis in the midsagittal plane assesses the prostate zone anatomy and capsular breach
• Rectal cancer staging — midsagittal MRI evaluates the tumour relationship to the anterior peritoneal reflection and levator ani
• Rectovesical pouch in abdominal trauma — free fluid (blood, bile, urine) collects in the most dependent peritoneal recess on midsagittal ultrasound

Part 5: Midsagittal Section of the Female Pelvis (AN51.2)

Female Pelvic Midsagittal Section — Structures From Anterior to Posterior

The female pelvis is more complex on midsagittal section because of the uterus and vagina between the bladder and rectum:

Anterior:
• Pubic symphysis
• Retropubic space
• Urinary bladder — slightly smaller than in males; the vesicouterine pouch (anterior pouch) lies between the bladder and the uterus; this pouch is less deep than in males

Middle structures:
• Uterus — normally anteverted (fundus tilts anteriorly over bladder) and anteflexed (angle at the internal os); cervix opens into the vagina at the vaginal vault
- Uterine positions: Anteverted + anteflexed (normal, 80%). Retroverted (20%) — fundus tilts backward, common and often incidental; can cause dysmenorrhoea and dyspareunia
• Vagina — connects the uterine cervix to the vulva; forms a 45° angle with the long axis of the uterus when anteflexed; related posteriorly to the rectovaginal pouch and rectum
• Vesicouterine pouch — small anterior peritoneal recess between bladder and uterus
• Rectouterine pouch (Pouch of Douglas / Cul-de-sac) — the MOST DEPENDENT peritoneal recess in the female pelvis; between the posterior uterus and anterior rectum; fluid (blood from ectopic rupture, pus in PID, ascites) collects here first

Posterior:
• Rectum — lies posterior to the vagina and uterus; separated from the vagina by the rectovaginal septum
• Sacrum and coccyx

Clinical relevance (Indian context):
• Ectopic pregnancy rupture — blood floods the pouch of Douglas first; diagnosed on transvaginal ultrasound as free fluid posterior to the uterus; emergency laparotomy
• Pelvic inflammatory disease (PID) — pus collects in the pouch of Douglas; culdocentesis (needle aspiration through the posterior vaginal fornix into the pouch) is used to confirm diagnosis
• Cervical cancer staging — MRI midsagittal plane shows the primary tumour, parametrial spread, and involvement of the bladder (anterior) and rectum (posterior)
• Uterine fibroid (leiomyoma) — the most common pelvic tumour in Indian women aged 30–50; midsagittal MRI shows submucosal, intramural, and subserosal locations