A Case Report of Calyceal Diverticulum: Differential Diagnosis for Organ-Preserving Operations

Abstract

Calyceal diverticula and epidermal cysts are extremely rare kidney lesions with unknown etiology and pathogenesis. They have non-specific clinical and radiological picture. Despite the benign nature, sometimes these disorders mimic malignant tumors leading to unjustified nephrectomy. We present a clinical and morphological observation of a multicystic lesion in a 76-year-old patient's right kidney filled with keratinized masses and imitating a malignant solid tumor. The detailed gross, histological and immunohistochemical (desmin, cytokeratin 7, uroplakin and p63) analyses of the kidney tissue excluded the malignant nature of the lesion. The final differential diagnosis was between an epidermal cyst and calyceal diverticulum with pronounced squamous cell metaplasia of urothelium. The upper pole localization of the lesion, its connection with the pelvicalyceal system through the unobstructed isthmus, the presence of urothelial lining and smooth muscle cells in its wall let us diagnose a calyceal diverticulum type I. Knowledge of the key clinical and morphological features of epidermal cysts and diverticula of the pelvicalyceal system will help the practicing physicians suspect the benign nature of such lesions and perform organ-preserving operations.

Keywords: calyceal diverticulum; intrarenal epidermal cysts; kidney; nephrectomy; simple renal cyst.

Figure 1

MRI of the patient's abdominal cavity (without contrast). (A) In the upper pole of the right kidney, the lesion of an irregular shape and inhomogeneous structure was connected with the pelvicalyceal system, coronal projection, SSFP mode. (B) The lesion had an irregular shape and a bumpy surface, 3D-reconstruction from the SSFP series. (C–E) The multinodular nature of the lesion and clear boundaries were determined in axial sections, T1 mode.

Figure 2

Fragments of the kidney and cystic lesion. Gross evaluation (A,B) demonstrates cystic lesion with adjacent renal parenchyma (p) separated by septa with varying wall thickness. Adhesions tightly connected the lesion with the kidney capsule and adjacent adipose tissue. The lumen was filled with gray-brown cheesy keratinized masses (k). It was connected to the small renal calyx (c) with the isthmus (i). Mucosa of the calyx was gray, smooth, with single overlays of horny masses. (C) The histological study revealed keratinized mass in the lumen of the lesion. (D) The renal parenchyma was separated from the cyst wall with adipose tissue of the renal sinus. (E,F) Three types of epithelium lined the cyst wall: stratified squamous epithelium (sq) with a developed granular layer and hyperkeratosis, urothelium (ur) and simple cuboidal epithelium (cub). (G) We also detected the focuses of chronic inflammatory infiltration. (H) Atrophic renal parenchyma was adjacent to the epithelial lining in some areas.

Figure 3

Immunohistochemical study of kidney cystic lesion. The cyst wall areas contained numerous smooth muscle cells (A), singular cells (B) or completely lacked the cells (C). (D–F) The cuboidal epithelium, urothelium and epithelium of the kidney tubules were strongly positive for CK7, while the stratified squamous epithelium did not express the marker. (G–I) The urothelium was positive for uroplakin III, while the cuboidal epithelium expressed this marker weakly and irregularly. (J–L) The multilayer squamous epithelium and tubule epithelium were not stained with antibodies against uroplakin III, but expressed p63. The cuboidal cyst epithelium had weak and focal positive expression of p63, the epithelium of the tubules was not stained.