SUN-097 - Giant Invasive Prolactinoma Presenting as Chronic Sinonasal Pressure

Giant invasive prolactinomas are rare pituitary neuroendocrine tumors that can mimic skull base malignancies due to extensive extrasellar extension, bony destruction, and neurovascular encasement. We present a case highlighting the importance of early endocrine evaluation and treatment with cabergoline.
A 48‑year‑old man with obesity and hypertension presented to his primary care physician with sinus pressure and left‑sided nasal obstruction and was referred to otolaryngology for presumed chronic sinusitis. Persistent symptoms prompted computed tomography (CT) imaging, which revealed a large destructive central skull base mass. Magnetic resonance imaging demonstrated a 5.9 × 5.0 × 5.3 cm sellar and central skull base lesion with obliteration of the sella, erosion of the clivus and sphenoid, invasion of the cavernous sinus, encasement of the carotid artery without stenosis, suprasellar extension with distortion of the optic apparatus, and involvement of the sinonasal and nasopharyngeal regions. The patient denied visual complaints, a formal ophthalmologic evaluation showed no signs of optic nerve involvement, papilledema or visual field defects.
Initial differential diagnosis included chordoma, chondrosarcoma, sinonasal carcinoma, metastatic disease, and aggressive pituitary tumor. Biopsy revealed a lactotroph pituitary neuroendocrine tumor with an elevated Ki‑67 proliferation index of 6.85%. Endocrine evaluation demonstrated a serum prolactin level exceeding 10,000 ng/mL after serial dilution, hypogonadotropic hypogonadism, and preserved adrenal and thyroid function, establishing the diagnosis of a giant invasive prolactinoma.
Treatment with cabergoline was initiated with planned dose escalation and close biochemical monitoring. Within three weeks of starting treatment, the patient reported resolution of nasal obstruction, suggesting early clinical response. Follow‑up CT imaging demonstrated decrease in tumor size to approximately 4.5 × 4.8 × 3.0 cm. After five weeks of therapy, the prolactin level decreased to 160.9 ng/mL. Due to marked sphenoid and clival erosion and history of unilateral rhinorrhea, the patient was recognized to be at high risk for cerebrospinal fluid leak during tumor shrinkage. The elevated proliferative index, optic apparatus distortion, and risk of CSF leak requires close multidisciplinary follow-up.
This case reinforces the need for early prolactin measurement with serial dilution in patients presenting with large invasive sellar or parasellar masses to avoid diagnostic delay and unnecessary surgical or radiotherapeutic interventions. Early symptomatic improvement, marked biochemical response, and rapid decrease in tumor measurements support cabergoline as an appropriate first-line therapy in giant invasive prolactinoma.

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