SAT335 Bilateral Pheochromocytomas In Multiple Endocrine Neoplasia Type 2B: A Frozen Abdomen, A Slow Growing Mass, And A Backdoor Solution

Abstract

Abstract Disclosure: O.A. Shariq: None. T.J. McKenzie: None. W.F. Young: None. Background: Multiple endocrine neoplasia type 2B (MEN2B) is most commonly caused by a germline methionine-to-threonine substitution at codon 918 (M918T) of the RET proto-oncogene. The syndrome is characterized by medullary thyroid carcinoma, pheochromocytoma, and extra-endocrine manifestations (intestinal ganglioneuromas, mucosal neuromas, and skeletal and ophthalmic abnormalities). We describe a patient with MEN2B and bilateral pheochromocytomas, in whom the slow-growing nature of the lesions, and previous history of an extra-endocrine manifestation, precluded the typical approach to surgical resection. Clinical Case: A 58-year-old-male with MEN2B, diagnosed at age 15, presented with a 6-month history of episodic palpitations and labile blood pressures. His past surgical history included a total abdominal colectomy and ileorectal anastomosis at age 7 years for megacolon, secondary to intestinal ganglioneuromatosis. He subsequently required multiple laparotomies and adhesiolysis procedures for recurrent small bowel obstructions. During his most recent laparotomy at age 44, he was noted to have a ‘frozen’ abdomen with dense adhesions involving the small bowel. CT abdomen revealed bilateral adrenal masses, measuring 2.9 cm and 1.5 cm on the right and left, respectively. Review of previous imaging revealed that the right adrenal mass had been present 16 years prior, measuring 1.0 cm at that time, while the left-sided mass was not seen. Biochemical workup was negative previously, but now showed elevated plasma metanephrine (4.1 nmol/L [N<0.5 nmol/L ]) and normetanephrine 2.3 nmol/L [N<0.9 nmol/L ]) levels. In the setting of extensive intra-abdominal adhesions and the slow-growing nature of both masses, the decision was made to perform a unilateral right adrenalectomy through a retroperitoneoscopic, rather than a transabdominal, approach. Pathology confirmed a 4.4 cm pheochromocytoma. The patient was discharged on postoperative day 1 and was symptom free at 1 year follow-up. His most recent plasma metanephrine and normetanephine levels were 0.7 nmol/L and 0.5 nmol/L, respectively. Clinical Lessons: Patients with MEN2B have a 50% lifetime risk of developing pheochromocytoma. Unlike medullary thyroid cancer, which exhibits an aggressive phenotype in this syndrome, MEN2B-associated pheochromocytomas may be slow growing, thereby avoiding the need for an initial bilateral adrenalectomy. Many patients with MEN2B develop gastrointestinal manifestations, including megacolon during infancy, for which multiple surgical interventions may be required. These procedures carry a risk of adhesion formation, which presents a challenge if further abdominal surgery is required later in life for pheochromocytoma. Retroperitoneoscopic adrenalectomy provides a safe approach in such patients, as the need to perform risky adhesiolysis and mobilize adjacent organs is obviated. Presentation: Saturday, June 17, 2023