Clinical diagnosis of ITGCN is based on surgical biopsy of the testes with immunohisto-chemical staining for placental alkaline phospha-tase (PLAP). It was originally thought that ITGCN was evenly dispersed throughout the testicle and a random biopsy would be adequate for diagnosis. This was challenged by later work that supported a focal or lobule arrangement of ITGCN [29]. Based on this knowledge, biopsy recommendations are to obtain a 3 x 3-mm section of tissue from the craniolateral portion of the testicle, which should minimize the risk to the intratesticular vessels. This size of tissue should be adequate to diagnose ITGCN if at least 10% of the testicular volume is involved [30]. Dieckmann and colleagues [31] determined the false-negative biopsy rate using this method to be less than 0.5%. They followed 1859 cases with a negative biopsy for ITGCN for 7 years, with 42 patients eventually developing TGCTs. Based on their data, testicular biopsy has a 91% sensitivity, and as high as a 99.5% specificity for the detection of ITGCN. Postulated reasons for false-negative biopsies are mechanical trauma to the specimen from surgical instruments, small biopsy size, sampling error, and improper fixation. For example, formalin causes excessive shrinkage of the tubules making the microscopic examination difficult. The preferred fixative is Stieve fluid (formol-sublimate) or Bouin's solution if the former is not available.

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