Isolated Neurohypophysial Sarcoidosis Involving the Cavernous Sinus Mimicking a Malignant Tumor.

Because of nonspecific clinical and radiological findings, it is difficult to diagnose isolated neurosarcoidosis without histological examination. Distinguishing neurosarcoidosis from neoplasm, infectious disease, or granulomatous disease can be challenging. In this study, we present a case of a 61-year-old female who presented with unilateral blindness. Magnetic resonance imaging (MRI) revealed a large invasive mass lesion located in the neurohypophysis with homogeneous enhancement after the injection of gadolinium. The lesion involved the bilateral cavernous sinus, which extended along the dura of the skull base with leptomeningeal lesions. Contrast-enhanced computed tomography (CT) and fluorodeoxyglucose positron emission tomography/CT of the entire body showed no other lesions. Biochemical examinations showed no useful data, including angiotensin-converting enzyme, β-glucan, soluble interleukin-2 receptor, and T-SPOT. Cerebrospinal fluid examination revealed only the elevation of total protein. Under the preoperative diagnosis of a malignant tumor or metastatic tumor, followed by tuberculosis, fungal infection, or granulomatous disease, a biopsy was performed to immediately determine the appropriate therapy, which revealed the histological diagnosis of sarcoidosis. After steroid therapy, the lesions had markedly shrunk as observed on MRI, and the eyesight of the patient's right eye was completely restored. In this case, without a biopsy, discriminating between sarcoidosis and a malignant tumor was difficult. We believe that a prompt histological diagnosis of an invasive isolated neurohypophysial mass lesion involving the bilateral cavernous sinus, which is similar to a malignant tumor, is essential for selecting the appropriate therapy.