On an axial MRI of the pelvis at the level of the acetabular roof, the obturator internus muscle is located:
- A Anterior to the hip joint, forming part of the anterior capsule
- B In the gluteal region, superficial to the piriformis
- C Lateral to the ischial spine, lining the lateral wall of the true pelvis and exiting via the lesser sciatic foramen ✓
- D Between the ischiorectal fossa and the anal canal
Correct answer: C. Lateral to the ischial spine, lining the lateral wall of the true pelvis and exiting via the lesser sciatic foramen
Explanation
The obturator internus lines the lateral wall of the lesser pelvis, arising from the obturator membrane and surrounding bony margins. It exits the pelvis through the lesser sciatic foramen, making a near-right-angle turn around the ischial spine before inserting into the greater trochanter. On axial MRI it appears as a thick muscle lining the lateral pelvic wall medial to the acetabulum. Piriformis exits through the greater sciatic foramen. The ischiorectal fossa contains the pudendal canal (Alcock's canal) in its lateral wall formed by obturator internus fascia.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.