Calyceal diverticula, also known as pyelocalyceal diverticula, are outpouchings of the renal calyx or pelvis into the renal cortex. These diverticula are lined with transitional cell epithelium.
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Epidemiology
Relatively uncommon, historically seen in 0.21% to 0.60% of intravenous urograms (IVU) 3. In 48.9% of the cases, it affects the upper pole of the kidney. In 29.7% and 21.4% of the cases it affects middle and lower poles respectively 3. Both kidneys have equal chances of being affected. In 3% of the cases, bilateral kidneys are affected 3. Average diverticulum sizes range from 0.5 to 7.5 cm 3.
Associations
gender: females are more commonly affected than men, with a ratio of 2:1 3
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9.5-50% chance of stone formation due to urine stagnation 3 ; average stone sizes range from 0.1 to 3.0 cm 3
Clinical presentation
The majority of cases are asymptomatic and discovered incidentally on imaging 3. Up to 50%, though, present with hematuria, calculi, flank pain and/or recurring infection.
Pathology
They may be congenital or acquired. The most common theory for the congenital origin of calyceal diverticula is a failure of regression of the third and fourth-generation ureteric buds 1. Acquired causes may occur secondary to infection, rupture of renal cyst, vesicoureteric reflux 6, or obstructing stones 1.
There are two categories of calyceal diverticula 1:
type I: more common, communicates with a minor calyx
type II: communicates with a major calyx or the renal pelvis and tends to be symptomatic
Radiographic features
Plain radiograph
Only a diverticulum containing milk of calcium will be visible on a plain radiograph. It appears as a meniscus-shaped density on an upright radiograph that changes its shape with changing position, i.e. either supine or decubitus radiographs.
Fluoroscopy
On intravenous urograms (IVU), calyceal diverticula fill on excretory phase and appear as opacified cystic cavities connecting with pelvicalyceal system.
Ultrasound
Calculi or layered dependent "milk of calcium" complicating a calyceal diverticulum appear echogenic on ultrasound 1, but only the former will cast an acoustic shadow.
CT
On non-contrasted CT, calyceal diverticulum appears as a cyst with high attenuating material within 1.
On nephrographic phase contrast-enhanced CT, a calyceal diverticulum will have an appearance similar to that of a simple cyst. The diagnosis is made with certainty in the excretory phase when the cystic structure fills with contrast material due to communication with the collecting system, and layering of contrast material is seen within. This helps differentiate it from a renal cyst, which does not connect with the collecting system.
Calculi or layered dependent milk of calcium complicating a calyceal diverticulum will be hyperattenuating on an unenhanced CT.
Complications
hemorrhage
infection
cyst rupture
malignancy (extremely rare) 1
Differential diagnosis
General imaging differential considerations include
focal calyectasis, most commonly renal tuberculosis 4
History and etymology
Calyceal diverticulum was first described by Rayer in 1841 3. The term "calyceal diverticulum" was first coined by Prader 3.