Type 2 calyceal diverticulum with an unusual appearance in the lower pole of the kidney

Abstract

A 45-year-old woman presented to our clinic with intermittent left flank pain. The family physician referred her for renal cystic mass with a calcified appearance. The non-contrast spiral abdominal computed tomographic (CT) scan demonstrated the mass-like cystic lesion with a densely calcified lesion in the lower pole of the kidney. A detailed history revealed that she underwent shock wave lithotripsy (SWL) for the lower pole renal stone one year ago. After SWL, the stone fragments migrated to the dependent diverticulum region and produced the misleading appearance of a Bosniak type III lesion. Contrast-enhanced computed tomography (CT) scan was done for further evaluation, and finally, the diagnosis of the calyceal diverticulum was confirmed in the lower pole of the kidney. Calyceal diverticula are the outpouching of the pyelocalyceal system lined by non-secretory transitional epithelium. It is a rare condition that occurs in less than 0.5% of the population. Most patients are asymptomatic and have been discovered incidentally in routine imaging modalities. As most of the patients are asymptomatic, many do not need intervention. However, in some instances, patients present with flank pain, hematuria, urinary tract infection, and stone formation in the diverticulum. They are in the differential diagnosis of renal cystic lesions such as simple renal cyst, renal cortical abscess, and parapelvic cyst. In renal cystic lesion besides of simple renal cyst or renal cystic mass, we should keep the differential diagnosis of the calyceal diverticulum type 2, especially in patients that underwent SWL for renal stones; the fragmented residual stone may have migrated to this dilated region and produce the deceptive appearance of a Bosniak type III lesion.

Keywords: Bosniak classification; Calyceal diverticulum type 2; Contrast-enhanced CT Scan; Hydrocalyx; Left renal cystic mass.

Figure 1. A 45-year-old woman with left calcified renal mass, turning out to be a type 2 calyceal diverticulum

Findings: A) Non-contrast renal CT scan (coronal view) reveals a mass-like lesion in the lower pole of the kidney that resembles a Bosniak type III lesion (red arrow) with a calcified area in the peripheral zone of the lesion (yellow arrow) B) The first spiral non-contrast renal CT scan (coronal view) before SWL reveals a cystic mass in the lower pole (red arrow) and renal stone in the lower pole (green arrow) Technique: Non-contrast spiral abdominal CT scan, coronal view (Multi-detector spiral CT, Siemens,64 slices, 2mm slice thickness, 110 kVp,120 mAs)

Figure 2. A 45-year-old woman with a left cystic renal mass in the lower pole of the left kidney, turning out to be a type 2 calyceal diverticulum

Finding: A cystic renal mass in the lower pole of the left kidney resembled severe hydronephrosis with the extension into the lower pole. A calcified area resembles a cystic lesion’s extension into the lower pole. Technique: Transabdominal ultrasound, 3.5MHZ, GE volusion S8 ultrasound machine

Figure 3. A 45-year-old woman with left cystic renal mass and renal stone, turning out to be a type 2 calyceal diverticulum

Findings:(A) Early phase after contrast administration revealed renal stone fragments in the center of a cystic lesion (red arrow) (B) Delayed phase of a contrast enhanced abdominal CT, the contrast filled the diverticulum cavity and revealed communication between the diverticulum and the calyceal system. Technique: Contrast abdominal CT scan, coronal view after administration of 70 ccs, visipaque contrast medium (Multi-detector spiral CT, Siemens,64 slices,5mm slice thickness,110 kVp,399 mAs)