CASE OF THE WEEK
2020-22 / June 1
(Contributors: William J. Anderson and Christopher D.M. Fletcher )
A woman in her 60s with a well circumscribed mass in the renal cortex.
Quiz
1. What is the diagnosis?
a. Solitary fibrous tumor
b. Leiomyosarcoma
c. Glomus tumor
d. Myopericytoma
e. Synovial sarcoma
1. a; 2. b; 3. d
1. Myopericytoma
Myopericytomas are benign mesenchymal neoplasms that show perivascular (pericytic) myoid differentiation and lie on a morphologic spectrum with myofibromas. They are most commonly seen in adults, and although the majority arise in the dermis or subcutis, they can rarely occur in the kidney and urinary tract, often as an incidentally discovered lesion.
Grossly, myopericytomas are well circumscribed but unencapsulated. Microscopically, they have a lobulated or multinodular architecture and are composed of bland ovoid to spindle-shaped cells that have a myoid appearance, pale eosinophilic cytoplasm, and indistinct cell borders. There are often prominent blood vessels of variable wall thickness, some of which may be hemangiopericytoma-like, around which the spindle cells may be arranged concentrically. This growth pattern may be particularly evident towards the periphery of the tumor. Rare examples are intravascular. By immunohistochemistry, myopericytomas show diffuse positivity for smooth muscle actin (SMA) and are usually also positive for h-caldesmon. A subset shows focal expression of desmin. Most commonly, myopericytoma/myofibroma harbors activating PDGFRB mutations.
1. Lau SK, Klein R, Jiang Z, Weiss LM, Chu PG. Myopericytoma of the kidney. Human Pathology. 2010;41(10):1500-4.
2. Sirohi D, Smith SC, Epstein JI, Balzer BL, Simko JP, Balitzer D, et al. Pericytic tumors of the kidney-a clinicopathologic analysis of 17 cases. Human Pathology. 2017;64:106-17.
3. Zhao M, Williamson SR, Sun K, Zhu Y, Li C, Xia W, et al. Benign perivascular myoid cell tumor (myopericytoma) of the urinary tract: a report of 2 cases with an emphasis on differential diagnosis. Human Pathology. 2014;45(5):1115-21.
4. Li J, Zhao M, Chen Z, Zou L, Teng X. Renal myopericytoma: a clinicopathologic study of six cases and review of the literature. International Journal of Clinical and Experimental Pathology. 2015;8(5):4307-20.
William J. Anderson and Christopher D.M. Fletcher
Brigham and Women’s Hospital
Boston, MA
wanderson@bwh.harvard.edu
Kidney
Kidney, myopericytoma, pericytic