Calyceal Diverticulum

Calyceal diverticula are outpouchings of renal calyces or even renal pelvis (pelvi-calyceal diverticula) into the renal cortex connected by narrow neck. These are lined by non-secreting urothelium (transitional cell epithelium).

Incidence: 0.2-0.6% of patients undergoing renal imaging.

Usually these are incidental findings and are mostly asymptomatic. Due to stagnation of urine within the diverticulum, these are prone for stone formation. Stones can be found in upto 50% of the calyceal diverticula.

Exact etiology of the formation of calyceal diverticula are not known, may be congenital or acquired due to infections, VUR, or rupture of a cortical cyst.

These are subdivided into two types:¹
Type 1 communicating with a calyx, usually found in upper pole.
Type 2 communicating with renal pelvis, larger, usually found in mid-pole (also called pyelo-calyceal diverticula). Radiopaedia adopts a slightly varied types, with type 1 from minor calyx and type 2 from major calyx or renal pelvis.²

There may be internal calcifications, either in the form of stones or of milk of calcium. In one small ultrasound series, 7 of 11 cases of calyceal diverticula demonstrated mobile echogenic material. It is suggested that the presence of mobile hyperechogenic material within a cystic structure is diagnostic of a calyceal diverticulum. ³

Differential considerations of a calyceal diverticulum would include complex cyst, dilated calyx, cystic renal neoplasm and abscess. Unless an excretory (or urogram) phase is acquired diagnosis of calyceal diverticulum is not possible. Dilated calyx can be due to obstructing stone, tumor or due to infundibular stenosis in TB.



The following plain and contrast CT images are of a 40 year old male patient who was evaluated for left lumbar pain and tenderness.

Plain CT Axial sections showing calcific focus within a subtle hypodense area in the bilateral renal parenchyma. 

Type I Bosniak cyst is noted medially (not marked).

The above three images shows the Plain CT, venous phase and excretory phase axial sections of both kidneys, which shows contrast filling of the cystic appearing area in the venous phase - consistent with the diagnosis of Calyceal Diverticulum of both kidneys. Calculus formation is noted in both these calyceal diverticulum. 

Oblique coronal MIP image showing the contrast filled bilateral calyceal diverticulum (Green arrows). The yellow arrow points to the pathology for which the patient underwent the CT examination (colitis). As in most cases, this case of bilateral calyceal diverticulum was also asymptomatic.  

3D VRT image demonstrating the calyceal diverticula. 

References
1. Mullett, Rebecca et al. “Calyceal diverticulum - a mimic of different pathologies on multiple imaging modalities.” Journal of radiology case reports vol. 6,9 (2012): 10-7. doi:10.3941/jrcr.v6i9.1123

2. Stunell, H et al. “The imaging appearances of calyceal diverticula complicated by uroliathasis.” The British journal of radiology vol. 83,994 (2010): 888-94. doi:10.1259/bjr/22591022

3. Reynard J, Brewster S, Biers S. Oxford Handbook of Urology. Oxford: Oxford University Press; 2006. p. 328.

4. Leveillee RJ, Bird VG. Treatment of Caliceal Diverticula and Infundibular Stenosis. In: Smith AD, Badlani G, Bagley D, et al., editors. Smith’s Textbook of Endourology. 2nd ed. Ontario: BC Decker; 2007. pp. 171–185.