Intrarenal epidermoid cyst mimicking a cystic renal cell carcinoma: A case report and review of literature

Key Clinical Message This case highlights the diagnostic pitfalls that can occur when evaluating complex cystic renal masses. Distinguishing epidermoid cysts from renal cell carcinoma is difficult but imperative to guide conservative management when appropriate, avoiding unnecessary nephrectomy. Abstract Renal epidermoid cysts are extremely rare, with only 12 cases reported in the literature. Their radiographic features often resemble cystic renal cell carcinoma, frequently prompting unnecessary nephrectomy. A 64‐year‐old man with a history of nephrolithiasis presented with left flank pain and hematuria. Imaging revealed a complex cystic renal mass suspicious for renal cell carcinoma. Following left radical nephrectomy, histopathology examination revealed a benign epidermoid cyst. Renal presentation of epidermoid cyst poses unique diagnostic and therapeutic challenges. Possible pathogenesis includes ectopic epidermal implantation during embryogenesis or squamous metaplasia following chronic irritation or deficiency. Radiographic distinction from concerning entities like renal cell carcinoma is difficult but imperative to avoid extensive surgery. This case highlights the diagnostic pitfalls and management considerations for renal epidermoid cysts. Additional study of clinical and imaging factors that distinguish epidermoid cysts from renal cell carcinoma can guide conservative management when appropriate, avoiding unnecessary nephrectomy for benign disease.


| INTRODUCTION
Epidermoid cysts are common cutaneous lesions but remarkably rare within the kidney.Their renal presentation poses unique diagnostic and therapeutic challenges. 1,2Radiographically, they often resemble more neoplastic processes like cystic renal cell carcinoma, frequently prompting unnecessary nephrectomy. 2Despite concerning imaging features, epidermoid cysts remain benign. 3pidermoid cysts and dermoid cysts represent distinct pathological entities, despite sharing some similarities.Epidermoid cysts are benign cystic lesions lined by stratified squamous epithelium and containing purely desquamated keratin material.][6][7][8] Their rarity, with only 12 documented in the literature, renders their precise pathogenesis and origin in the kidney unclear.Accurate diagnosis is imperative to avoid extensive surgery and preserve renal function.Here, we present a case of a renal epidermoid cyst, accompanied by a comprehensive literature review to further characterize these uncommon intrarenal cysts.

| CASE HISTORY
A 64-year-old man with a past medical history of hypertension, horseshoe kidney, and two prior open nephrolithotomies presented with left flank pain radiating to the left lower quadrant of abdomen and microscopic hematuria.
The physical examination was unremarkable.Computed tomography (CT) imaging demonstrated a 60 × 60 × 55mm lobulated cystic lesion in the upper pole of the left kidney, with foci of calcification and heterogeneous density.No measurable enhancement was seen, although mild thickening and enhancement of the cyst wall were noted (Figure 1).
Given radiographic suspicion for a cystic renal cell carcinoma, the patient underwent a left radical nephrectomy.Gross pathological examination of the nephrectomy specimen revealed a well-circumscribed cystic structure protruding from the kidney parenchyma.Sectioning displayed a unilocular cyst filled with soft and waxy yellowish material.Microscopic analysis demonstrated a cyst wall lined by stratified squamous epithelium with a granular layer, with no atypia, and filled with laminated keratin debris (Figure 2).To differentiate between an epidermoid cyst and a dermoid cyst, the entire cyst wall was embedded and examined microscopically.It did not show any skin appendages, consistent with the diagnosis of an epidermoid cyst.

| CONCLUSION AND RESULTS
The patient had an uncomplicated postoperative course.

| DISCUSSION
In this article, we report a case of a 64-year-old man with a history of prior nephrolithotomies who presented with left flank pain and microscopic hematuria.The imaging characteristics and clinical presentation strongly suggested a malignant cystic neoplasm that was followed by radical nephrectomy.][11][12] The pathogenesis of epidermoid cysts of the kidney remains controversial, with several theories proposed to explain their histogenesis.One prevailing theory suggests that these cysts are formed due to atypical ectodermal placement during the embryonic stage, particularly from residual Wolffian duct tissues. 2 According to this perspective, the misplaced ectodermal cells contribute to the presence of epidermal tissue fragments within the renal architecture, which subsequently evolve into epidermoid cysts. 3,13Moreover, squamous metaplasia has been proposed as the etiology of renal epidermoid cysts.This pathological change can be of traumatic or deficiency origin. 1 On one hand, the traumatic origin is associated with prolonged irritation induced by renal stones and by treatments like shock wave lithotripsy. 12On the other hand, the deficiency origin is linked to vitamin A deficiency, which is known to induce keratinizing squamous metaplasia in the urothelium. 1,2,14As mentioned in our case presentation, our patient did not have any history of trauma but did have a prior history of nephrolithotomy.Given this clinical context, the possible pathogenesis and etiology of the epidermoid cyst of our case could be attributed to chronic irritation and squamous metaplasia secondary to nephrolithiasis.
The radiographic evaluation of renal epidermoid cysts poses a diagnostic challenge due to their similar features with other renal conditions. 2 Epidermoid cysts of the kidney typically appear on imaging as cystic lesions with irregular contours and possible stippled or coarse calcifications in the cyst wall or lumen, thus they can mimic more concerning renal masses like renal cell carcinoma. 1Radiographically, differentiation between epidermoid and dermoid cysts on MRI can be facilitated by observing signal intensities; typically, epidermoid cysts exhibit hyperintense signals on diffusion-weighted imaging (DWI) and are hypointense on T1-weighted F I G U R E 2 (A) Gross specimen shows cystic lesion arising from the upper pole of the kidney.The mass has a smooth, glistening outer surface and measures approximately 6 cm in greatest dimension.The cyst was filled with soft and waxy yellowish material.(B) Microscopic image, H&E stain, 40× magnification.The cyst is lined by stratified squamous epithelium with a granular cell layer, filling the cystic space.Underneath the squamous epithelium lining, glomeruli and tubules can be noticed.images, whereas dermoid cysts generally display hyperintense signals on T2-images due to their higher fat content. 2,15ther key entities in the differential diagnosis of a cystic renal mass with calcification include teratomas, tuberculomas, Wilms tumors, xanthogranulomatous pyelonephritis, and osteogenic sarcoma metastases. 3,16,17orrelation with clinical findings can help distinguish epidermoid cysts from more worrisome renal masses when the imaging appearance is equivocal.

T A B L E 1
In conclusion, we present a challenging case of an epidermoid cyst that was diagnosed as renal cell carcinoma based on concerning radiographic features.This case highlights the diagnostic pitfalls that can occur when evaluating complex cystic renal masses.Additional study is imperative to identify imaging and clinical factors that can help distinguish these entities, guiding appropriate management.This can facilitate conservative management when appropriate and avoid extensive surgery for benign disease.

F
I G U R E 1 (A) Coronal contrastenhanced CT image demonstrates a large, lobulated cystic mass in the upper pole of the left kidney.(B, C) Axial contrastenhanced CT (B) and non-contrast CT (C) image shows a well-circumscribed cystic lesion in the upper pole of the left kidney.
Reported cases of renal epidermoid cyst.