Recurrent flank pain from 'lobster claw'.

A 56-year-old woman with sickle-cell trait (hemoglobin electrophoresis with 53.5% hemoglobin A, 3.7% hemoglobin A2, 41.7% hemoglobin S and 1.1% hemoglobin F) was seen for recurrent episodes of ‘bilateral’ flank pain associated with gross hematuria and passage of cellular debris. These episodes had occurred on an infrequent basis for many years and seemed to be triggered by fasting. Her past medical history was pertinent for osteoarthritis and nephrolithiasis. She was on no medications and did not use any non-steroidal anti-inflammatory drugs or other over-the-counter medications. Physical examination was unremarkable. Renal function was normal (serum creatinine of 0.7 mg/dL). Hematocrit was 34.8. There was no proteinuria. A computed tomographic urogram (CTU) of abdomen demonstrated bilateral papillary necrosis.

Papillary necrosis reflects ischemic damage to renal medulla. Sickling facilitated by hyperosmotic, hypoxic and acidotic environment of the medulla leads to infarct. Diabetes mellitus, analgesic abuse, pyelonephritis, renal vein thrombosis, tuberculosis and obstructive uropathy are other major causes of papillary necrosis. Multidetector-row CTU helps in the detailed assessment of the renal parenchyma and collecting system and facilitates identification of papillary necrosis at a very early stage [1].

Necrosis of the papilla causes swelling followed by shrinkage of the papilla with widening of the fornices. The necrotic papilla may either remain in situ or detach and form a cavity. Necrosis may be limited to the central tip of the papilla (medullary form) or involve the entire papilla (total papillary necrosis) [2]. Radiographically, tracks of contrast arising from the fornices of blunted calyces are seen. Sloughed papillae are seen as central filling defect with a surrounding ring of contrast. Figures 1 and 2 show the typical ‘egg in a cup’ appearance with central pooling of contrast and ‘lobster claw’ pattern of contrast extravasation seen in papillary necrosis [3].

Fig. 1.

(A) CTU with intravenous contrast demonstrating bilateral papillary necrosis (3D reconstruction) shows the ‘egg in a cup’ appearance with central contrast pooling (long arrow, left), ring shadow of sloughed papilla with central lucency (arrow head) and ‘lobster claw’ with horns of contrast from the fornices (short arrow, right). (B) CTU with intravenous contrast demonstrating normal papilla illustrates the appearance of a normal papilla on a CTU (3D reconstruction).

Fig. 2.

CTU with intravenous contrast demonstrating bilateral papillary necrosis (coronal section) shows the ‘egg in a cup’ appearance with central contrast pooling (long arrow, left), ring shadow of sloughed papilla with central lucency (arrow head) and ‘lobster claw’ with horns of contrast from the fornices (short arrow, right).