Answer: Mesonephric hyperplasia

Histology: Infiltrating within several of the TUR chips are small tubules that have a basophilic appearance at low magnification. The tubules are not organized in a lobular growth pattern, but rather infiltrate haphazardly within the stroma. The tubules are characterized by scant cytoplasm. The nuclei appear uniform and benign. Within many of the tubules are dense colloid secretions. There is no stromal reaction to the tubules. Focally, one can appreciate that these tubules have a papillary component, also lined by atrophic epithelium.

Discussion: Adenosis consists of a lobular collection of glands with abundant cytoplasm, in contrast to what is seen in the current case. All of the individual glands seen in this case are atrophic; the infiltrative appearance of this lesion is inconsistent with benign prostatic atrophy. Furthermore, the dense eosinophilic secretions are unique and not seen within prostatic atrophy. Because of the infiltrative nature of this lesion, architecturally it resembles adenocarcinoma of the prostate. Some adenocarcinomas of the prostate may contain atrophic cytoplasm. However, in order to diagnose atrophic adenocarcinoma of the prostate, one typically needs to see prominent cytologic atypia within the atrophic appearing glands. Furthermore, atrophic adenocarcinoma typically merges in with adenocarcinoma showing more typical abundant cytoplasm. In the current case, there are no cytologic features of malignancy, ruling out atrophic adenocarcinoma. Features seen in this case are typical of mesonephric hyperplasia. Mesonephric hyperplasia is a rare entity that we initially reported on in 1993. The case illustrated is another case that I recently saw. The characteristic findings of mesonephric hyperplasia include a proliferation of small tubules lined by atrophic cytoplasm with bland nuclei. Typically, these tubules will have dense colloid secretions as seen in the current case. The presence of some dilated glands with micropapillary formation is also a typical feature that is not seen in adenocarcinoma of the prostate. In one of the prior cases that we reported on, glands of mesonephric hyperplasia were present within large nerves and ganglion tissue, further mimicking adenocarcinoma. Mesonephric hyperplasia typically occurs up near the bladder neck and around the seminal vesicle. Stains for prostate specific antigen and prostate specific acid phosphatase are negative, which may also help to exclude the diagnosis of adenocarcinoma of the prostate.