Answer: Myxoid adrenal cortical neoplasm

Histology: Microscopically, the lesion shows a number of architectural patterns, including anastomosing cords of eosinophilic polygonal cells with pinpoint nucleoli floating loosely in an acellular myxoid background and small nests of similar cells separated from stroma by small amounts of myxoid matrix. Additionally, a distinct pseudoglandular pattern with myxoid luminal contents was noted in multiple areas. Finally, cellular trabeculae separated by delicate fibrovascular septae, with cytologic similarity to adrenal cortical cells, and focally interdigitating with normal adrenal cortical tissue were distinguished. The lesion showed limited pleomorphism, rare mitoses and no evidence of vascular/capsular invasion or necrosis.

Discussion: The transitional areas between the myxoid areas and the normal adrenocortical tissue identify this tumor as being of adrenocortical origin. Myxoid neoplasms of the adrenal cortex are rare entities, with only nineteen reported cases, and account for just 4.7% of 300 adrenocortical neoplasms in the single published series. Patients range in age from 16 to 73 years, with a female predominance. The nineteen reported cases include eight adenomas and eleven carcinomas. Both non-functioning and functioning lesions have been reported. Features that reliably differentiate adrenocortical adenomas from carcinomas have been controversial. Although tumor size has been considered the most reliable predictor of malignancy, up to 13.5% of resected adrenocortical carcinomas are < 5cm, making size alone an insufficient criterion. Similarly, using a weight cutoff of 100 g to distinguish adenoma from carcinoma is inadequate, as both adenomas weighing > 100 g and carcinomas weighing < 100 g have been described. In two studies, Weiss et al defined eleven pathologic parameters to be evaluated in adrenocortical neoplasms, with three or more criteria associated with a malignant phenotype. These included high nuclear grade, mitotic rate > 5 per 50 HPF, presence of atypical mitoses, clear cells comprising < 25% of the tumor, diffuse architecture, microscopic necrosis, venous, sinusoidal and capsular invasion, tumor weight and size. The latter study also demonstrated that only mitotic rate had a strong association with patient outcome in adrenocortical carcinomas, as >20 mitoses per 50 HPF was associated with a median survival of 14 months, as opposed to 58 months for those patients with < 20 mitoses. The adrenal neoplasm described currently was clinically nonfunctional and showed a grossly identifiable myxoid component. Overall, the tumor was 70% myxoid and demonstrated a variety of architectural patterns including pseudoglandular features. Even in light of the criteria described by Weiss, considerable difficulty remains in differentiating benign from malignant adrenal tumors, specifically in cases, like this one, of large tumors without marked invasive features and cellular atypia. Although the infrequent mitoses and lack of diffuse pleomorphism, necrosis, vascular or capsular invasion favor a benign behavioral patter for this lesion, the large tumor weight and dimensions make definitive prediction of a benign clinical course challenging. Reference(s): - Brown FM, Gaffey TA, Wold LE, Lloyd RV. Myxoid neoplasms of the adrenal cortex. A rare histologic variant. Am J Surg Pathol. 2000;24:396-401. - Weiss LM. Comparative histologic study of 43 metastasizing and nonmetastasizing adrenocortical tumors. Am J Surg Pathol. 1984;8:163-169. - Weiss LM, Medeiros LJ, Vickery AL Jr. Pathologic features of prognostic significance in adrenocortical carcinoma. Am J Surg Pathol. 1989;13:202-206.