Cranial Nerve VI Palsy as a Presenting Sign of Previously Undiagnosed Metastatic Prostate Adenocarcinoma to the Clivus

Introduction: Prostate adenocarcinoma is the most common cancer in males in the United States with an annual incidence of 110 per 100,000 males annually. Typically, highly curable prostate adenocarcinoma is the second leading cause of cancer-related death due to metastatic disease to the bone in 86% of cases. There has, however, been only three reported cases of metastatic prostate adenocarcinoma to the clivus. Here we present the case of a male who presented with a cranial nerve VI palsy with imaging showing an infiltrative skull mass, who was ultimately diagnosed with prostate adenocarcinoma metastatic to the clivus.

Case Report: An 81-year-old male with history of prostate adenocarcinoma status-post radiation three years prior presented to the emergency department for evaluation of diplopia. Of note, the patient was on enzalutamide for rising prostate-specific antigen in the absence of known active disease. His examination showed partial right abducens palsy on extreme lateral gaze, and he had no other focal neurological deficits. A noncontrast computed tomography scan of the sinuses was performed which showed a 2.5 × 3.5 × 3.9 cm midline skull base mass involving the sella and suprasella (image 1) and he was subsequently admitted to the hospital for further work-up. He was unable to undergo a magnetic resonance imaging at that time as it was thought his stainless prostate seeds were a contraindication. Therefore, based on CT scan, differential included pituitary adenoma, meningioma, hematologic malignancy, chondrosarcoma, chondroma, and metastatic disease. Endocrinology was consulted given concern for secreting pituitary adenoma, with no evidence of endocrine dysfunction. Due to inability to perform further imaging, decision was made to take the patient to the operating room and obtain a biopsy for definitive diagnosis. An anterior skull base approach was performed, the sella was entered, and biopsies were taken. Intraoperative frozen section showed atypical epithelioid neoplasm, with final pathology confirming a diagnosis of metastatic prostatic adenocarcinoma. He was subsequently cleared to undergo MRI, which demonstrated an infiltrative mass of the clivus extending to the petrous apices, cavernous sinus, petrous and cavernous internal carotid arteries, prepontine cisterns, and abutting the pituitary gland (image 2). The patient was thus referred to radiation oncology for palliative radiation.

Conclusion: Prostate adenocarcinoma is the leading cause of cancer in males and metastatic disease can involve the skull base in unique circumstances. Few case reports exist of prostate adenocarcinoma metastatic to the clivus. Here we add to this literature by presenting a case of a patient with isolated cranial nerve VI palsy as the presenting sign of previously undiagnosed metastatic prostate adenocarcinoma involving the clivus. The skull base surgeon should maintain a high clinical suspicion for metastatic disease as a cause of atypical sellar and suprasellar lesions.

Fig. 1 Noncontrast enhanced CT at the level of the pituitary gland shows a 2.5 × 3.5 × 3.9 cm midline skull base mass involving the sella and suprasella.

Fig. 2 MRI of the head with and without IV contrast demonstrating diffuse metastatic infiltration and destruction of the clivus.