[An unusual complication after an insect bite? Diagnostic procedures in a case of granular cell tumor].

Granular cell tumors are, in almost all cases, benign soft tissue tumors, although malignant variants have rarely been described in a variety of anatomical locations. In the case presented here, a so-called atypical granular cell tumor was diagnosed based on two criteria, being differentiated from the usual histological findings by enhanced mitotic activity and focal spindle cell proliferation. Further suspicious characters of the tumor were its size of 13x10x5 cm on MRT as well as its long-term clinical course (1.5 years). The diagnostic procedures undergone until resection of the tumor, including the macroscopic and histological findings, are presented. The diagnosis can be made with certainty by using conventional histology in combination with immunohistochemistry. The tumor cells react positively with antibodies against S-100 protein, NSE, laminin, myelin proteins and myelin-associated glycoproteins. These staining patterns underscore the neural origin of the tumor tissue. In this case a mitotic frequency of two per ten high power fields and focal spindle cells led to the diagnosis of an atypical granular cell tumor, whereas the criteria for a malignant variant were not met.