Original Article Calcification and ossification in conventional schwannoma: A clinicopathologic study of 32 cases Nasir U. Din, 1 Karen Fritchie, 2 Muhammad U. Tariq, 1 Arsalan Ahmed 1 and Zubair Ahmad 1 1 Department of Pathology and Laboratory Medicine, Aga Khan University Hospital, Karachi, Pakistan and 2 Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA Calcification and ossification are uncommon in schwannomas; however, when present these findings may cause diagnos- tic confusion with other mesenchymal tumors which more frequently harbor these features. We sought to better characterize the type and rate of calcification and ossifi- cation in schwannomas. Cases of schwannoma diagnosed at our institution from 2005 to 2019 were reviewed to determine the type and amount of calcification and ossifi- cation present. Of 2116 total cases of schwannoma reported during the study period, 38 cases harbored calci- fication or ossification per the pathology report. Thirty- two of the 38 cases had slides available for review, of which 27 (84.3%) showed calcification, nine showed ossi- fication (28.1%), and four (12.5%) cases demonstrated both. Foci of ossification typically occurred adjacent to large vessels. Of the 27 cases showing calcification, coarse dystrophic calcification was seen in 22 cases, psammomatous calcification in nine cases, and combined dystrophic and psammomatous calcification was seen in four cases. Cases with psammomatous calcification pre- dominantly occurred in spinal roots and cerebellopontine angle of a younger age group with almost equal gender distribution. All four cases tested for protein kinase cyclic adenosine monophosphate-dependent type I regulatory subunit alpha immunohistochemical stain demonstrated retained expression. We confirm that calcification and ossification are rare findings in schwannoma. Awareness that these features may be present in these tumors will prevent misdiagnosis and ensure appropriate clinical management. Key words: calcification, dystrophic, ossification, psammomatous, schwannoma. INTRODUCTION Schwannomas are encapsulated nerve sheath tumors com- posed entirely of differentiated Schwann cells. Degenera- tive change is well recognized in these tumors and includes the presence of various types of calcification. While the finding of dystrophic calcification in schwannomas rarely results in diagnostic difficulty, these tumors may also harbor psammomatous calcification which may raise the possibility of malignant melanocytic nerve sheath tumors. Malignant melanocytic nerve sheath tumors typically occur in the vicinity of autonomic or spi- nal nerves and harbor psammoma bodies in up to 50% of cases. 1 Unlike schwannomas, which are benign and can be managed by conservative resection, malignant melanocytic nerve sheath tumors may show aggressive behavior with recurrence and metastatic rates that reach 40% in some studies. 2 Additionally, these neoplasms may be associated with Carney complex. 1 Schwannomas may also have foci of ossification, a feature rarely reported in these neo- plasms, potentially causing confusion with other matrix- forming mesenchymal tumors. We sought to study the presence of calcification and ossification in schwannomas to determine the rate of matrix production in these lesions as well as highlight the diagnostic challenges that may arise when these changes are present. MATERIALS AND METHODS The anatomic pathology archives of the Aga Khan Uni- versity Hospital in Karachi were queried for cases diag- nosed as “schwannoma” from June 2005 through June 2019. The surgical pathology reports of these cases were reviewed, and the hematoxylin and eosin (HE)-stained slides of schwannomas showing calcification and/or ossifi- cation per the histologic description within the surgical pathology report were retrieved. The slides of all retrieved cases were reviewed by two of the authors (NU and ZA) to confirm the diagnosis of schwannoma and determine the type and amount (percentage) of calcification and/or ossification present in each case. Calcification was Correspondence: Muhammad U. Tariq, MBBS, FCPS, Section of His- topathology, Department of Pathology and Laboratory Medicine, Aga Khan University Hospital, P.O box 3500, Stadium Road, Karachi 74800, Pakistan. Email: mohammad.usman@aku.edu Received 14 August 2019; revised 25 September 2019; accepted 16 October 2019. Neuropathology 2019 doi:10.1111/neup.12622 © 2019 Japanese Society of Neuropathology