Synchronous Pelvic Schwannoma With Metastatic Prostate Cancer: A Rare Case and Pathology Review.

Schwannomas are benign tumors arising from well-differentiated Schwann cells of peripheral nerves. They are usually found on the limbs, head, and neck. It is uncommon for schwannoma to occur in the pelvis and when it does, it is often diagnosed late. Pelvic schwannoma when diagnosed are often bigger in size (>5 cm) and may present with local symptoms such as constipation and bladder outlet obstruction. We hereby present a patient with concurrent metastatic prostate carcinoma and pelvic schwannoma. The patient is a 57-year-old man initially diagnosed with prostate cancer and was lost to follow-up. One year later, he presented with metastatic prostate disease and bladder outlet obstruction. Further evaluation revealed a concurrent pelvic mass that was increasing in size. The biopsy of this mass was suggestive of schwannoma. It was decided at the multidisciplinary tumor board conference to offer treatment for his metastatic prostate disease and observe the schwannoma. His obstructive symptoms worsened in the face of clinical evidence of regression of his prostatic disease, and it was decided to resect the pelvic mass. The surgery revealed a huge soft tissue mass within the pelvis that was adherent to the bladder, prostate, and rectum. Morphology and immunohistochemistry studies of the pelvic mass confirmed the diagnosis of ancient schwannoma. We hereby highlight the clinical importance of this presentation and the diagnostic and therapeutic dilemma involved in the management of this patient who presented with two pathologic conditions causing similar symptoms but of different prognostic and therapeutic significance.