Large pelvic plexiform schwannoma presenting with a perineal bulge in a child: A case report

Plexiform schwannoma (PS) is a rare tumor that accounts for only 5 % of all schwannomas. Most cases are small, measuring less than 3 cm in diameter, and involve the skin and superficial tissue of the head, neck, or trunk. The location of the pelvis is extremely rare for PS and even so for ordinary schwannomas. We report on our case of a four-year-old Arabic boy who presented with a palpable mass in the perineum. This was found to represent an extrapelvic extension of a large intrapelvic plexiform schwannoma measuring 8 cm in maximum dimension on magnetic resonance imaging (MRI). A diagnosis of plexiform neurofibroma was suspected. However, the mass was surgically resected and histologically confirmed to be benign PS. The location of the pelvis is extremely rare for PS and this clinical presentation with a perineal mass is unique to our case. Distinguishing PS from plexiform neurofibroma or malignant peripheral nerve sheath tumor is of utmost clinical importance. However, the preoperative diagnosis is often challenging due to nonspecific imaging features. The MRI findings highlighted here may help in the preoperative diagnosis of this rare pelvic tumor.