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CASE OF THE WEEK

A male patient in his 50s underwent robotic radical prostatectomy for prostatic carcinoma. The index tumour was present in the right posterolateral peripheral zone, Grade Group 2 (Gleason sore 3+4=7, 20% Gleason pattern 4). The images are from different regions in the left posterior aspect towards the base, both within the prostate and in extraprostatic fat. A male patient in his 50s underwent robotic radical prostatectomy for prostatic carcinoma. Contributors :

Laurence A Galea (1), Shekib Shahbaz (2)
1. Department of Anatomical Pathology, Melbourne Pathology, Sonic Healthcare, Victoria, Australia
2. Melbourne Urology Centre, Victoria, Australia.

Twitter handle: @DrLaurenceGalea

Quiz Questions

What is the most likely immunohistochemical stain in the last Figure?
a. ERG
b. SALL4
c. NKX3.1
d. GATA3
e. PAX8

What is the correct diagnosis?
a. Nephrogenic metaplasia/adenoma
b. Atrophic prostatic adenocarcinoma
c. Prostatic postatrophic hyperplasia
d. Mesonephric remnant hyperplasia
e. Prostatic simple atrophy

Quiz Answers

1. e
2. d.

Diagnosis

1. PAX8
2. Mesonephric remnant hyperplasia

Discussion

The microscopic images show mesonephric remnant hyperplasia (MRH) with mostly lobular architecture composed of small tubules and acini with luminal colloid-like secretions; and lined by a single layer of cuboidal cells with round nuclei, inconspicuous nucleoli and scant cytoplasm. Focally MRH formed nodules with minimal tubule formation. All foci demonstrated diffuse PAX8 expression while NKX3.1 was negative. High molecular weight keratin 34 beta E12 was positive and p63 was negative.

Mesonephric remnants are benign, similar to the female genital tract counterpart and believed to represent embryologic remnants [1]. In a series of radical prostatectomy specimens by Chen YB et al. MRH was identified posteriorly towards the base (as in the current specimen) and in the anterior fibromuscular stroma and adjacent anterolateral periprostatic tissue [2].

The most clinically important differential diagnosis of MRH is prostatic carcinoma (PC). Atrophic PC exhibits more cytological atypia with occasional prominent nucleoli and is usually associated with more typical less atrophic carcinoma. MRH exhibits less cytological atypia with regular round nuclei and inconspicuous nucleoli. PAX8 is positive in MRH while NKX3.1 is negative. Basal markers are less helpful as p63 is usually negative and 34e12 can be negative in MRH [1-2]. Nephrogenic metaplasia/adenoma (NM) can mimic MRH morphologically, particularly if the tubules are cystically dilated and contain colloid-like secretions. It is also PAX8 positive/NKX3.1 negative. However, NM occurs in the periurethral tissue and does not infiltrate extraprostatic tissue. Also NM can have a peritubular hyaline rim and the tubules can be lined by hobnail cells. Distinguishing MRH from prostatic glandular atrophy and postatrophic hyperplasia can be challenging though dictinction is not as clinically significant. They both exhibit lobular architecture and atrophic glands can be cystically dilated, but are NKX3.1 positive/PAX8 negative, as opposed to MRH [2].

References

1. Bostwick DG, Qian J, Ma J, Muir TE. Mesonephric remnants of the prostate: incidence and histologic spectrum. Mod Pathol. 2003 Jul;16(7):630-635.
2. Chen YB, Fine SW, Epstein JI. Mesonephric remnant hyperplasia involving prostate and periprostatic tissue: findings at radical prostatectomy. Am J Surg Pathol. 2011 Jul;35(7):1054-1061.

Contributors

Laurence A Galea (1), Shekib Shahbaz (2)
1. Department of Anatomical Pathology, Melbourne Pathology, Sonic Healthcare, Victoria, Australia
2. Melbourne Urology Centre, Victoria, Australia.

Twitter handle: @DrLaurenceGalea

Organ Site

Prostate

Keywords

Mesonephric remnant hyperplasia, atrophy, nephrogenic metaplasia, nephrogenic adenoma