MON-097 - Pituitary Metastasis from Probable Lynch Syndrome Presenting with Panhypopituitarism and Harlequin Syndrome in the Postpartum Period

This is a case of a 29-year-old female diagnosed in the postpartum period with an extremely rare condition of pituitary metastasis from probable Lynch syndrome, presenting with panhypopituitarism, Harlequin syndrome, and multiple other metastatic sites.

The patient had a strong maternal family history of colorectal cancer and a one-year history of hematochezia prior to presentation. During an emergency cesarean section for premature labor, an abdominal mass was incidentally noted. In the postpartum period, she developed diplopia and ptosis, and imaging revealed a sellar mass invading the pituitary gland and cavernous sinus. Further evaluation demonstrated a circumferential rectosigmoid tumor with extensive hepatic, pulmonary, osseous, and pituitary metastases. Rectal biopsy showed mismatch-repair–deficient colorectal adenocarcinoma with isolated PMS2 loss, supporting a diagnosis of probable Lynch syndrome in the absence of germline genetic testing. Biopsy of the sphenoid sinus lesion confirmed metastatic colorectal origin.

Clinically, the patient manifested unilateral facial flushing consistent with Harlequin syndrome, a highly unusual autonomic neurologic manifestation of pituitary metastasis, likely due to disruption of sympathetic fibers within the cavernous sinus. Endocrine evaluation revealed panhypopituitarism. Despite prompt hormonal replacement and palliative surgical intervention, the disease followed an exceptionally aggressive course, and the patient died from septic shock during hospitalization.

This case highlights an extremely rare endocrine manifestation of metastatic colorectal cancer, the diagnostic challenges of postpartum sellar lesions, and the importance of recognizing panhypopituitarism and rare autonomic signs as potential indicators of pituitary metastasis. Early identification of hereditary colorectal cancer syndromes and timely surveillance remain essential to improving outcomes in high-risk individuals.

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