Teaching Case

A 43-year-old female patient presented at the emergency room with left flank pain for the last two days. On clinical examination, she was apyretic and with no costovertebral angle tenderness.
The patient had a history of recurrent renal infections.

Plain abdominal radiograph was the first radiological investigation performed, which showed a calcium content projected in the region of the left kidney (Fig. 1). The patient was referred to the urinary stone ambulatory consultation, having performed several sessions of extracorporeal shock wave lithotripsy, however, with maintenance of the calcification on plain abdominal radiographs.
A diagnostic ureteroscopy did not reveal endoluminal changes. During the procedure, after contrast administration via the ureteroscope, a fluoroscopic study showed normal opacification of the collecting system (Fig. 2).
Therefore, a computed tomography urography (CTU) was performed, showing a well-defined, thin-walled and low-density structure, located at the upper pole of the kidney, that contained calcific density in the pending position - “milk of calcium”. Following intravenous contrast, the structure gradually filled with contrast, indicating a connection with the collecting system (Fig. 3) - diagnostic of calyceal diverticulum.

The calyceal diverticulum is an uncommon disorder, which consists of a small urine-filled cavity within the renal parenchyma, developed as an outpouching of the renal calyceal system, communicating with it via a narrow isthmus. The diverticulum typically ranges from 0.5 to 2.0 cm in diameter and it is often unilateral. The diverticula´s aetiology can be congenital, obstructive (e.g. stone), traumatic or fibrotic. [1-3]
Calyceal diverticula are classified in two types: type 1, the more common form, communicates with a minor calyx or an infundibulum and is often located at the upper pole of the kidney; type 2 is larger, tends to be symptomatic and communicates directly with the renal pelvis or a major calyx, commonly at the mid-pole of the kidney. [2, 4]
Up to 50% of calyceal diverticula contain stones or “milk of calcium”, precipitated by urinary stasis within the diverticulum. [4]

The majority of patients with calyceal diverticula are asymptomatic. The symptoms may arise from the development of stones and urinary tract infections, such as flank pain and haematuria. [2, 5]

The imaging studies that may be used in assessing include:
- Plain film radiography: Calyceal diverticula are not seen, but if calcifications are present, these may be visible. A diverticulum containing “milk of calcium” appears as a meniscus-shaped density with a fluid-calcium level at the upper margin. [1, 2]
- Ultrasound: A calyceal diverticulum appears as a cyst-like lesion. The patient should be scanned in both the supine and prone position to determine the presence of mobile calculi or “milk of calcium” within a cystic structure, which is diagnosis of calyceal diverticulum. [1, 4]
- CTU: The calyceal diverticulum appears as a well-defined, thin-walled and low-density structure. The calcific content, if present, should lie dependently within the cystic structure. On contrast-enhancement study, the structure should gradually fill with contrast, as it leaves the normal calyx, being more evident in the late phase. This indicates a connection with the collecting system. [1, 4]
- Intravenous Urography (IVU) is used less commonly in current practice, due to the increasing use of ultrasound and CTU. However, calyceal diverticulum may be readily demonstrated on IVU and may be diagnostic. [1]

Historically, the treatment of symptomatic patients included open surgery, however, current practice involves less invasive techniques, including stone removal via shock wave lithotripsy, ureteroscopic lithotripsy, percutaneous nepholithotomy or laparoscopic removal. An asymptomatic calyceal diverticulum usually does not need intervention. [2, 6]

Calyceal diverticula are commonly incidental findings. Recognition of classical findings may help to differentiate these from more serious pathology.