Indian Journal of Pathology and Microbiology

: 2017  |  Volume : 60  |  Issue : 4  |  Page : 571--573

Epidermoid cyst of the renal pelvis masquerading as malignancy

Dinesh Pradhan1, Gabriela Quiroga-Garza1, Ronald Hrebinko2, Rajiv Dhir1, Anil V Parwani3,  
1 Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
2 Department of Urology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
3 Department of Pathology, Ohio State University Wexner Medical Center, Columbus, OH, USA

Correspondence Address:
Dr. Dinesh Pradhan
Department of Pathology, University of Pittsburgh Medical Center, 200 Lothrop Street, Pittsburgh, PA 15213


Epidermoid cyst of the renal pelvis is exceptionally rare. The histogenetic mechanism has not been well characterized. Herein, we report a case of intrarenal epidermoid cyst in a 62-year-old woman who had undergone left nephrolithotomy for a staghorn calculus. She was being followed up for bilateral renal cysts when a complex mass was noted arising from the lower pole of the left kidney. Renal ultrasound showed a small left kidney with a solid vascular echogenic mass. A laparoscopic radical nephrectomy was performed. Gross examination revealed a well-circumscribed cystic mass with friable tan-yellow contents. Microscopically, a cystic structure lined by mature epidermis without atypia indicating epidermoid cyst was noted. The lesion appeared to be in continuity with the pelvicalyceal urothelium which displayed extensive squamous metaplasia. The patient is disease free and is doing well. Better clinical awareness of this benign entity and a preoperative biopsy may help preserve a kidney.

How to cite this article:
Pradhan D, Quiroga-Garza G, Hrebinko R, Dhir R, Parwani AV. Epidermoid cyst of the renal pelvis masquerading as malignancy.Indian J Pathol Microbiol 2017;60:571-573

How to cite this URL:
Pradhan D, Quiroga-Garza G, Hrebinko R, Dhir R, Parwani AV. Epidermoid cyst of the renal pelvis masquerading as malignancy. Indian J Pathol Microbiol [serial online] 2017 [cited 2023 Sep 29 ];60:571-573
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Full Text


Epidermoid cyst of the kidney is a rare entity, and only nine cases have been reported in the English literature.[1],[2],[3],[4],[5],[6],[7],[8],[9] The cyst has a wall comprising of epidermal lining and the lumen filled with laminated horny keratinous material. The proposed histogenetic mechanisms include derivation from epidermal remnants of the Wolffian duct, secondary to traumatic implantation of epithelium during external manipulation, or pelvic extension of the metaplastic squamous epithelium of the ureter due to prolonged irritation by calculi.[4],[5],[10] Although the intrarenal epidermoid cyst is extremely rare, it has a major clinical implication. Being unequivocally benign, it can be managed appropriately by a partial nephrectomy or renal preservation surgery if the preoperative diagnosis is made beyond doubt.[10] However, as the lesion mimics a neoplasm radiologically, it usually leads to unwarranted nephroureterectomy or nephrectomy. Herein, we report a case of intrarenal epidermoid cyst detected radiologically as a malignant lesion in a patient with nephrolithiasis and bilateral renal cysts.

 Case Report

A 62-year-old woman with a long-standing history of hypertension, hyperlipidemia, and chronic kidney disease and who had undergone left anatrophic nephrolithotomy for a staghorn calculus several decades before was being followed up for bilateral renal cysts (left-sided larger than right-sided one) and renal insufficiency. Her history was also significant for recurrent urinary tract infections for several years and microhematuria. Recent workup demonstrated a complex 6.5 cm mass arising from the lower pole of her atrophic left kidney. Renal ultrasound showed a small (11.7 cm × 5.6 cm × 6.3 cm) left kidney (cortex: 1.9 cm) with a solid vascular echogenic mass (5.8 cm × 4.3 cm × 4.2 cm) in the posterior lateral aspect. A noncontrast computerized tomography scan revealed a heterogeneous mass with predominant fluid density and focal coarse calcifications. Clinically, it was considered a Bosniak 3–4 cystic renal mass with a 50%–90% possibility of malignancy. A split differential renal function nuclear medicine scan indicated that 70% of her overall function is contributed by the uninvolved right kidney and 30% from the left kidney. Her two recent glomerular filtration rate estimates were 46 mL/min/1.73 m2 and 70 mL/min/1.73 m2, indicating that she will not need dialysis following left nephrectomy. Therapeutic options were discussed including continued surveillance, percutaneous biopsy, and partial or radical nephrectomy. A decision of radical nephrectomy was taken by the urology team as the left kidney was much scarred from previous surgery and the mass was too deep and large for a partial nephrectomy. In addition, the left kidney was poorly functioning to begin with and the glomerular filtration rate from the right side was sufficient to keep her from needing dialysis.

A laparoscopic left radical nephrectomy was ultimately performed after thorough workup.

 Pathology Findings

The left nephrectomy specimen measured 10.5 cm × 6.5 cm × 6.3 cm and was grossly deformed. The cut surfaces revealed a well-circumscribed, lower pole cystic mass (6.0 cm × 5.0 cm × 4.5 cm) with friable tan-yellow contents [Figure 1]. In addition, tan-white friable patches were noted in the proximal ureter. There was relatively scant amount of uninvolved red-brown renal parenchyma with indistinct corticomedullary junction and relatively dilated pelvicalyceal system. Microscopy revealed a cystic structure lined by mature squamous epithelium with granular layer and with compact lamellated keratinous material deposition confirming an epidermoid cyst. No atypia, dysplasia, or carcinoma was identified in the multiple tissue sections submitted for examination [Figure 2]. The lesion was intimately adherent to the adjacent kidney and appeared to be in continuity with the pyelocalyceal and ureteric urothelium, which also displayed extensive keratinizing squamous metaplasia. The ureter also revealed mild and focal papillary hyperplasia. The adjoining atrophic renal parenchyma exhibited a simple renal cyst and features of chronic pyelonephritis. The postsurgical follow-up was uneventful, and she is disease free for the last 1 year.{Figure 1}{Figure 2}


As the name suggests, epidermoid cyst is a very common lesion of the skin, formed by the downgrowth and cystic enlargement of the epidermis or of the hair follicle and mostly result from implantation of epidermis into the dermis. It has a wall composed of epidermal lining and the cystic lumen is filled with laminated strands of keratin. The intrarenal epidermoid cyst is a very rare entity. Although it microscopically mimics its dermatologic counterpart, the histogenetic mechanism remains unclear. It has been postulated that epidermal embryonic remnants derived from the Wolffian ducts may be the source of the renal epidermal cyst. Another school of thought proposes traumatic implantation of epithelial cells during renal operation to be the culprit. The extension of squamous metaplastic changes from the upper ureter to the pelvicalyceal system in prolonged irritative conditions such as nephrolithiasis is considered another plausible explanation.[4],[5],[9],[10] The latter may be the best explanation for the histogenesis of epidermoid cyst in the present case.

The clinical symptoms of intrarenal epidermoid cyst in a few cases described so far includes flank pain in seven cases [1],[3],[4],[5],[6],[7],[10] and painless gross or microscopic hematuria in two cases [2],[8] while it was asymptomatic and detected on radiologic examination as a renal pelvic mass in two cases [9] including the present case.

Only three cases of epidermoid cyst in the renal pelvis have been reported till date.[5],[9],[10] Two of them also exhibited a complex cyst in association with nephrolithiasis like the present case.[5],[10] To the best of our knowledge, this case of an epidermoid cyst in the renal pelvis is the fourth report in the English literature.


Intrarenal epidermoid cyst is a totally benign lesion which may mimic malignancy on radiologic examination and thus may lead to unnecessary nephrectomy. Better clinical awareness of the entity and a preoperative biopsy may help preserve a kidney.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.


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