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Diagnosis: Renomedullary interstitial cell tumor (or medullary fibroma)

Renomedullary interstitial cell tumor, or medullary fibroma, is a very frequent small tumor that presents as an incidental finding. The lesion localizes in the renal medulla and almost always measures less than 0.5 cm. in diameter, although tumors up to 6.5 cm have been reported.

The lesion is composed of stellate or polygonal cells embedded in a loose fascicular stroma. Is frequent to find thick bands of eosinophilic collagen or hyalinization areas, as seen in Figures 4, 5, and 8. Usually there are entrapped medullary tubules at the periphery, as seen in Figure 5. Some lesions are hypocellular and others contain amyloid.

Renomedullary interstitial cells are modified (or specialized) fibroblasts that regulate blood flow, water and salt absorption, and ultimately blood pressure through synthesis and secretion of prostanoids in which cycloxygenases play the rate-limiting steps (Gatalica Z, et al. COX-2 gene polymorphisms and protein expression in renomedullary interstitial cell tumors. Hum Pathol. 2008 Jul 10. [Epub ahead of print] [PubMed link]).

Due to the cellular aspect of the lesion and the main cell composing it: fibroblasts, the lesion is also known as medullary fibroma, a more simple name that facilitate understanding of the tumor.

In an autopsy series by Warfel and Eble renomedullary interstitial cell tumor was identified in almost 50% of patients older than 20 years of age (referenced in: Jennette et al (Editors). Heptinstall's Pathology of the Kidney, 6th edition, p. 1520).

In the differential diagnosis this tumor should be distinguished from metanephric stromal tumor, in this there is the characteristic formation of concentric rings or collarettes of stromal cells around entrapped renal tubules and blood vessels.

This tumor does not produce clinical alterations and it does not require a specific treatment.

See the chapter [Renal Neoplasms] with atlas and text (only in spanish).

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References

• Gatalica Z, Lilleberg SL, Koul MS, Vanecek T, Hes O, Wang B, Michal M. COX-2 gene polymorphisms and protein expression in renomedullary interstitial cell tumors. Hum Pathol. 2008 Jul 10. [Epub ahead of print] [PubMed link]
• Dall'Era M, Das S. Benign medullary fibroma of the kidney. J Urol. 2000;164(6):2018. [PubMed link]
• Zhuo JL. Renomedullary interstitial cells: a target for endocrine and paracrine actions of vasoactive peptides in the renal medulla. Clin Exp Pharmacol Physiol. 2000;27(7):465-73. [PubMed link]
• Mai KT. Giant renomedullary interstitial cell tumor. J Urol. 1994;151(4):986-8. [PubMed link]
• Cormier P, Patel SK, Turner DA, Hoeksema J. MR imaging findings in renal medullary fibroma. AJR Am J Roentgenol. 1989;153(1):83-4. [PubMed link][Free full text]
• Mandal AK. The renal papilla and hypertension: an up-to-date review. Pathol Annu. 1981;16(Pt 2):295-313. [PubMed link]
• Martin MR, Tiltman AJ. Incidence of renomedullary interstitial cell tumours and correlation with hypertension. S Afr Med J. 1976;50(53):2099-100. [PubMed link]
• Heptinstall RH, Salyer DC, Salyer WR. Experimental hypertension. The effects of chemical ablation of the renal papilla on the blood pressure of rats with and without silver-clip hypertension. Am J Pathol. 1975;78(2):297-308. [PubMed link] [Free full text]

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