Catecholamine-Producing Adrenal Schwannoma: A Rare Pheochromocytoma Imposter

Background:Adrenal schwannoma is a tumor of the adrenal medulla that poses a pre-operative diagnostic challenge due to its non-specific imaging findings and rarity. Even more uncommon are functional catecholamine-producing adrenal schwannomas (CPAS) that can lead to the clinical presentation of catecholamine excess. Here, we present a case of biochemically and histopathologically confirmed CPAS and provide a review of the existing cases in the literature. Clinical Case: A 43-year old woman with a history of hypertension was incidentally found to have a 4 cm left adrenal lesion. Computed tomography of the mass demonstrated indeterminate enhancement and washout characteristics. Upon evaluation, she had episodes of palpitations and fatigue without headache or flushing. Her medications were notable for metoprolol, vortioxetine, and lisdexamfetamine. Laboratory results were notable for elevated 24-hour urine metanephrine and normetanephrine of 551 mcg/24hr (normal: 58–203 mcg/24hr) and 927 mcg/24hr (normal: 88–649 mcg/24hr) respectively. Due to the possibility of pheochromocytoma, the patient elected for surgery and underwent laparoscopic left adrenalectomy after pre-treatment with an alpha-1-antagonist. Pathology demonstrated a 4.8 cm well-circumscribed tumor arising from the adrenal medulla that showed mostly hypercellular areas of spindled cells with wavy nuclei and focal nuclear palisading along with hypocellular areas with loose edematous stroma with focal areas of calcification and microcyst formation. IHC of the tumor cells was diffusely positive for S-100 and SOX-10, consistent with adrenal schwannoma. Laboratory results approximately 2 months post-operative on the same medications demonstrated normalization of 24-hour urine metanephrine and normetanephrine, confirming CPAS. A search of PubMed was performed using the search terms “adrenal schwannoma,” which returned 41 reports, of which 2 confirmed CPAS. Of the 3 cases, including ours, patients had a mean age of 44 years old and M:F ratio of 1:2. Each of the 3 tumors were left-sided with sizes ranging from 4.8 cm to 7.7 cm, which were all surgically removed. In the two previously published reports, the reported pre-operative laboratory markers were serum catecholamines and urine catecholamines, respectively, but neither compared levels to a reference range. In all cases, catecholamine levels normalized following surgical removal. Conclusion: Adrenal schwannoma is a rare entity in the differential diagnosis of non-functioning adrenal incidentaloma, but it should be considered for catecholamine-producing adrenal tumors as well. A summary of published cases suggests that these are typically large tumors with possible female predominance. This case is the first to document levels of catecholamine metabolite concentrations in CPAS.