MON-113 - The Silent Giant": Giant Lactotroph Pitnet with Modest Prolactin Presenting with Apoplexy and Malignant Cerebral Edema

Background

Lactotroph pituitary neuroendocrine tumors (PitNETs) in men often present as large, invasive lesions due to delayed diagnosis, resulting in significant morbidity. In giant tumors, serum prolactin concentrations may be disproportionately modest relative to tumor burden, leading to diagnostic uncertainty. Pituitary apoplexy is uncommon, and ischemic stroke with malignant cerebral edema is an exceptionally rare associated complication.

Case

A 29-year-old man with poorly controlled type 2 diabetes mellitus presented with sudden loss of consciousness, severe headache, and visual disturbance, without prior symptoms of hyperprolactinemia. Serum glucose exceeded 400 mg/dL without ketoacidosis. Neuroimaging revealed a giant sellar–suprasellar mass measuring 4.1 × 6.1 × 4.0 cm with right cavernous sinus invasion.

Endocrine evaluation showed prolactin 186.6 ng/mL, hypogonadotropic hypogonadism (total testosterone 2 ng/dL), IGF-1 169 ng/mL (Z-score 0.1), morning cortisol 11.5 µg/dL, and preserved thyroid function. Prolactin elevation was not attributable to an immunoassay hook effect, as serial dilution testing produced comparable results. Stress-dose glucocorticoids were initiated for suspected pituitary apoplexy, and MRI confirmed intratumoral hemorrhage.

Urgent endoscopic endonasal decompression with partial tumor resection was performed. Postoperatively, the patient developed an acute ischemic stroke involving the right basal ganglia and internal capsule, complicated by malignant cerebral edema requiring emergent right decompressive hemicraniectomy. Immediate postoperative imaging demonstrated tumor reduction to 2.8 cm in craniocaudal diameter.

Histopathology revealed a lactotroph PitNET with dense prolactin immunoreactivity and PIT-1 positivity, Ki-67 < 3%, and wild-type p53 expression. Tumor cells expressed somatostatin receptors SSTR2 and SSTR5. Postoperatively, prolactin normalized to 6.3 ng/mL, and panhypopituitarism developed, requiring chronic glucocorticoid and thyroid hormone replacement. Cabergoline was initiated and titrated to 2 mg/week.

Follow-up MRI showed continued tumor reduction from 1.8 × 1.6 × 1.1 cm at three months to 1.6 × 1.9 × 0.7 cm at six months, consistent with dopamine agonist responsiveness.

Conclusion

This case illustrates a high-risk lactotroph PitNET characterized by marked biochemical–radiographic discordance, catastrophic apoplexy complicated by ischemic stroke and malignant cerebral edema, and substantial endocrine morbidity despite low-risk histopathologic features. Clinical behavior and radiographic response should guide management more strongly than proliferative indices alone. Early recognition of modest prolactin elevation in giant pituitary tumors is essential to prevent delayed diagnosis and fatal outcomes.

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