Case Report | Open Access
A Rare Case of Multifocal Prostatic Blue Nevus
Prostatic blue nevus is a rare benign pathologic diagnosis most commonly diagnosed incidentally on many different types of prostate specimens. Blue nevus is the deposition of stromal melanin characterized by spindle cells within the fibromuscular stroma which stains positive for melanin-specific stains Fontana-Masson and S100 and stains negative for CD68, HMB45, and iron stains. We report the case of a multifocal and bilateral blue nevus in a 52-year-old Hispanic male who presented with an elevated prostate-specific antigen of 4.3 and mild obstructive lower urinary tract symptoms, found by transrectal ultrasound-guided prostate needle biopsy. The biopsy also revealed benign prostatic tissue with postatrophic hyperplasia and chronic inflammation. This is the 35th reported case of prostatic blue nevus and the third to show multifocal blue nevus.
Melanocytic lesions are an often-overlooked pathologic process that occurs in the prostate. Of these extremely rare lesions, the most commonly found is the prostatic blue nevus, also known as pigmented melanocytosis or prostatic pigmentary nevohyperplasia . Blue nevus is the deposition of stromal melanin characterized by spindle cells within the fibromuscular stroma which stains positive for melanin-specific stains Fontana-Masson and S100, while it stains negative for CD68 proteins, HMB45, and iron stains . Blue nevus is asymptomatic and benign and has been incidentally diagnosed following prostatectomy (11 cases), transurethral resection of the prostate (TURP, 6 cases), autopsy (5 cases), and transrectal ultrasound-guided prostate needle biopsy (TRUS PNBx, 2 cases) (Table 1).
AA, African American; H, Hispanic; W, non-Hispanic White, TURP, transurethral resection of the prostate.
2. Case Presentation
A 52-year-old healthy Hispanic male presented to an outpatient urology clinic with an elevated prostate-specific antigen (PSA) of 4.1 along with mild obstructive lower urinary tract symptoms. There was no family history of prostate cancer. The physical examination including the digital rectal examination was unremarkable. The patient was seen again 3 months later with a PSA of 4.3 and after discussion with the patient he elected to undergo a 12-core TRUS PNBx. The following month when the biopsy was performed, the PSA had slightly decreased to 3.4. The prostate was visualized in the sagittal and transverse planes via ultrasound probe and was unremarkable. Volume was measured to be 33 cm3 (PSA density of 0.10 ng/mL/g). Final pathology demonstrated blue nevus in one out of six cores on the right and two out of six cores on the left. On microscopic analysis with hematoxylin-eosin stain, individual heavily pigmented spindle cells distributed in between prostatic stroma and glands were noted (Figures 1 and 2). The remaining specimen consisted of benign prostatic tissue with postatrophic hyperplasia and chronic inflammation. The patient’s voiding symptoms improved with terazosin and no further workup was undertaken. The patient is now being followed up for routine prostate cancer surveillance as per the American Urological Association (AUA) guidelines .
Blue nevus is a rare lesion of dermal melanocytes most commonly found in the skin, but it has been reported in the oral mucosa, sclera, cervix, vagina, and prostate . The appearance of this lesion in nonintegumentary tissues is not fully understood; the prevailing hypothesis is that melanoblasts originate in the neural crest and migrate with the mesoderm into connective tissue, where they remain latent until maturing into melanocytes . Proliferation induced by inflammation or other insults of these latent melanoblasts can explain acquired cases of blue nevi . An alternative hypothesis proposes development from the neoplastic growth of Schwann cells of dermal nerves which became melanogenetic as they proliferated .
Blue nevus grossly appears as multiple brown to black streaks or nodules that range in size from 0.1 cm to 2.0 cm . Microscopically, prostatic blue nevus consists of stromal cells that contain finely granular brown or black pigment, which may also be seen in the extracellular matrix . The cells can extensively infiltrate the surrounding fibromuscular stroma individually or as irregularly clustered collections . The pigment-laden cells are usually spindle in shape with bipolar, elongated dendritic cytoplasmic processes but can also be round, ovoid, or polygonal (Figures 1 and 2). The nuclei have been described as centrally located and often obscured by the abundant melanin present in the cytoplasm . It is also important to recognize the benign nature of these lesions and not confuse them with more aggressive melanocytic lesions of the prostate such as malignant melanoma. Hypercellularity, diffuse atypia, increased mitotic activity, and positive immunostaining for HMB45 should help in differentiating malignant melanoma from blue nevus.
Review of the literature indicates that blue nevus typically presents as a single focus and is characteristically diagnosed on TURP and prostatectomy specimens. Although no risk factors for blue nevus have been identified, our discovery of just the second case in a Hispanic male may suggest variability in risk among different races/ethnicities . Of the other 34 reported cases of blue nevus, only two have shown multifocal blue nevus [24, 25]. Diagnosis is most often made on prostatectomy or TURP specimens; however, there have been two reported cases documenting diagnosis by TRUS PNBx, making this the third reported case [18, 19]. As in all other cases, blue nevus presented in an asymptomatic fashion. The importance of this case lies in the rarity of such a diagnosis as it is highly likely that both urologist and pathologist alike have not come across such a diagnosis. The recognition of the benign nature of blue nevus and multifocal blue nevus need to be emphasized as further workup and surveillance outside of routine prostate cancer screening carries no benefit. As always, all routine prostate cancer screening should follow the shared decision-making mantra endorsed by the AUA .
Conflicts of Interest
The authors declare that there are no conflicts of interest.
- V. L. Dailey and O. Hameed, “Blue nevus of the prostate,” Archives of Pathology & Laboratory Medicine, vol. 135, no. 6, pp. 799–802, 2011.
- G. Nigogosyan, S. De La Pava, J. W. Pickren, and M. W. Woodruff, “Blue nevus of the prostate gland,” Cancer, vol. 16, no. 9, pp. 1097–1099, 1963.
- R. A. Guillan and S. Zelman, “The Incidence and Probable Origin of Melanin in the Prostate,” The Journal of Urology, vol. 104, no. 1, pp. 151–153, 1970.
- W. Jao, D. F. Fretzin, M. L. Christ, and L. M. Prinz, “Blue nevus of the prostate gland,” Archives of Pathology, vol. 91, no. 2, pp. 187–191, 1971.
- W. A. Gardner and W. U. Spitz, “Melanosis of the Prostate Gland,” American Journal of Clinical Pathology, vol. 56, no. 6, pp. 762–764, 1971.
- N. L. Block, D. Weber, and R. Schinella, “Blue Nevi and Other Melanotic Lesions of the Prostate: Report of 3 Cases and Review of the Literature,” The Journal of Urology, vol. 107, no. 1, pp. 85–87, 1972.
- J. W. Langley and S. Weitzner, “Blue Nevus and Melanosis of Prostate,” The Journal of Urology, vol. 112, no. 3, pp. 359–361, 1974.
- M. Tannenbaum, “Differential diagnosis in uropathology III. Melanotic lesions of prostate: Blue nevus and prostatic epithelial melanosis,” Urology, vol. 4, no. 5, pp. 617–621, 1974.
- C. N. Rios and J. R. Wright, “Melanosis of the Prostate Gland: Report of a Case with Neoplastic Epithelium Involvement,” The Journal of Urology, vol. 115, no. 5, pp. 616-617, 1976.
- J. Kovi, A. G. Jackson, and M. A. Jackson, “Blue nevus of the prostate: ultrastructural study,” Urology, vol. 9, no. 5, pp. 576–578, 1977.
- J. Y. Ro, D. J. Grignon, A. G. Ayala, S. F. Hogan, B. Tetu, and N. G. Ordonez, “Blue nevus and melanosis of the prostate. Electron-microscopic and immunohistochemical studies,” American Journal of Clinical Pathology, vol. 90, no. 5, pp. 530–535, 1988.
- A. R. Botticelli, C. Di Gregorio, L. Losi, R. A. Fano, and A. Manenti, “Melanosis (pigmented melanocytosis) of the prostate gland,” European Urology, vol. 16, no. 3, pp. 229–232, 1989.
- S. Lew, S. Richter, N. Jelin, and A. Siegal, “A blue naevus of the prostate: a light microscopic study including an investigation of S‐100 protein positive cells in the normal and in the diseased gland,” Histopathology, vol. 18, no. 5, pp. 443–448, 1991.
- C. Martinez Martinez, R. Garcia Gonzalez, and A. Castañeda Casanova, “Blue Nevus of the Prostate: Report of Two New Cases with Immunohistochemical and Electron-Microscopic Studies,” European Urology, vol. 22, no. 4, pp. 339–342, 2017.
- F. Vesga Molina, M. Acha Pérez, R. Llarena Ibarguren, and C. Pertusa Peña, “Intraprostatic blue nevus,” Archivos Españoles de Urología, vol. 48, no. 10, pp. 985-986, 1995.
- E. Redondo Martínez, A. Rey López, and C. Díaz Cascajo, “Blue nevus of the prostate. Differential diagnosis of prostatic pigmented lesions,” Archivos Españoles de Urología, vol. 51, no. 3, pp. 286–289, 1998.
- C. Cuervo Pinna, E. Godoy Rubio, J. L. Parra Escobar, E. Sánchez Blasco, J. Valverde Valverde, and J. Moreno Casado, “Prostatic blue nevus. Terminology standardization of prostatic pigmented lesions,” Actas Urológicas Españolas, vol. 25, no. 3, pp. 245–247, 2001.
- F. Di Nuovo, M. G. Sironi, and M. Spinelli, “True prostatic blue nevus associated with melanosis: case report, histogenesis and review of the literature,” Advances in Clinical Pathology, vol. 6, no. 3-4, pp. 135–139, 2002.
- P. A. Humphrey, Prostate Pathology, American Society for Clinical Pathology, Chicago, Ill, USA, 2003.
- D. Anderco, E. Lazăr, S. Taban, F. Miclea, and A. Dema, “Prostatic blue nevus,” Romanian Journal of Morphology and Embryology, vol. 51, no. 3, pp. 555–557, 2010.
- R. Kudva and P. Hegde, “Blue nevus of the prostate,” Indian Journal of Urology, vol. 26, no. 2, pp. 301-302, 2010.
- M. R. Raspollini, L. Masieri, N. Tosi, and M. Santucci, “Blue nevus of the prostate: incidental finding in radical prostatectomy specimen with a pre-operative echographic image of peripheral hypoechogenic nodule,” Archivio Italiano di Urologia e Andrologia, vol. 83, no. 4, pp. 210–212, 2011.
- N. Montalvo and L. Redrobán, “Unusual histopathological diagnosis of prostatic blue nevus: a case report,” Journal of Medical Case Reports, vol. 7, no. 1, 2013.
- R. Ponte, J. L. Ravetti, M. Pacella, and C. Toncini, “Multifocal blue nevus of the prostate: a case report,” Analytical and Quantitative Cytology and Histology, vol. 36, no. 6, pp. 335–338, 2014.
- R. Ponte, J. L. Ravetti, P. Calamaro, M. Pacella, and C. Toncini, “Another case of multifocal blue nevus of the prostate,” Analytical and Quantitative Cytology and Histology, vol. 38, no. 1, pp. 57-58, 2016.
- H. B. Carter, “American urological association (AUA) guideline on prostate cancer detection: Process and rationale,” BJU International, vol. 112, no. 5, pp. 543–547, 2013.
- K. J. Craddock, B. Bandarchi, and M. A. Khalifa, “Blue nevi of the Müllerian tract: case series and review of the literature,” Journal of Lower Genital Tract Disease, vol. 11, no. 4, pp. 284–289, 2007.
- M. Ahmad and W. M. Reams, “The development of melanoblasts from leg bud mesenchyme grown in the celom of chick embryos,” Annals of Anatomy, vol. 143, no. 5, pp. 501–508, 1978.
- Y. Hori, M. Kawashima, K. Oohara, and A. Kukita, “Acquired, bilateral nevus of Ota-like macules,” Journal of the American Academy of Dermatology, vol. 10, no. 6, pp. 961–964, 1984.
- T. Nakai and H. Rappaport, “A study of the histogenesis of experimental melanotic tumors resembling cellular blue nevi: The evidence in support of their neurogenic origin,” The American Journal of Pathology, vol. 43, pp. 175–199, 1963.
Copyright © 2018 Elias J. Farran et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.