Distinguishing spheno-orbital metastatic prostate cancer mimicking a meningioma using novel 18F-PSMA PET/CT imaging.

A 78-year-old man presented with acute-onset left temporal pain, eyelid swelling, and double vision. Computed tomography (CT) demonstrated a left sphenoid wing mass with extra-osseous intra-orbital and intracranial extension, thought to be a typical sphenoid wing meningioma by the primary team. The patient was admitted for an urgent craniotomy, which was planned for the following day. However, upon consultation with ophthalmic plastic surgery, concern was raised for an alternative diagnosis given the atypical timeline, inflammatory changes, and uncharacteristic imaging findings of mixed lytic and sclerotic bony changes without hyperostosis on CT and extensive peri-lesional dural thickening and enhancement on magnetic resonance imaging. A serum prostate-specific antigen was elevated to 206 ng/mL. Subsequent positron emission tomography (PET)/CT using 18F-fluorodeoxyglucose radiotracer was negative for metastatic disease. A prostate-specific membrane antigen (PSMA) PET/CT was then obtained and demonstrated extensive metastases. An orbital biopsy revealed poorly differentiated prostatic adenocarcinoma. The significant incongruence between the standard PET/CT and PSMA PET/CT highlights the value of this novel advanced radiographic modality in narrowing the differential diagnosis and determining the extent of disease. Findings of widespread metastasis on the PSMA PET/CT ultimately helped to avoid a large, morbid neurosurgical intervention in this patient, allowing for a minimally invasive orbital biopsy to characterize the tumor for therapeutic targeting.