Interstitial Cell Tumor, Testis, Rat

Interstitial or Leydig’s cell tumors in the rat testes vary in size, ranging up to 40 mm in diameter. When the tumors are small, they are usually present as multiple homogeneous nodules. Large tumors are well circumscribed and the cut surface is yellow to yellow- brown, which is clearly demarcated from the gray background of normal testis. These large tumors may replace the entire testis and usually contain multiple cystic areas filled with clear or hemorrhagic fluid (Fig. 214).