A case of giant prolactinoma, initially misdiagnosed as sinonasal neuroendocrine carcinoma

Abstract

Abstract Giant prolactinomas are defined as pituitary tumors greater than 4 cm, often associated with very high prolactin level (> 1000 ng/mL). They are relatively rare tumors and can present differently from typical prolactinomas. They can be highly invasive, resulting in acute neurological complication at the time of presentation. We present a case of a young woman with giant prolactinoma initially misdiagnosed as sinonasal neuroendocrine carcinoma. The acute presentation of headache, ptosis and impending brain herniation, requiring emergent ventriculostomy and intubation, led to the clinical suspicion of a more sinister diagnosis. Transnasal biopsy of the mass was consistent with sinonasal neuroendocrine carcinoma, and chemotherapy was planned. Laboratory testing, however, revealed an elevated prolactin (27,400 ng/mL, after 1:100 dilution). Re-review of pathology with additional immunohistochemical staining was requested and confirmed the diagnosis of prolactinoma. After 5 months of cabergoline treatment, prolactin level has decreased to 118 ng/mL. There has been a marked reduction in tumor size and an almost complete resolution of neurological symptoms. Given their atypical presentation and potential for sharing common immunohistochemical stains with other neuroendocrine neoplasms, giant prolactinomas extending into the nasal cavity can be misdiagnosed as other neuroendocrine neoplasms which may develop at this site. Accurate diagnosis is imperative to prevent unnecessary surgery and/or radiation and to ensure implementation of dopamine agonist therapy.