Egg in a cup.

A case of medullary type papillary necrosis diagnosed on nephrostogram is presented showing characteristic egg-in-cup appearance.

INTRODUCTION

Papillary necrosis can be seen in various pathologic conditions. The medullary form consists of central necrosis at the tip of the renal pyramid and gives rise to a characteristic egg-in-cup appearance on contrast studies.

CASE REPORT

A 39-year-old male patient presented with fever, left flank pain, nocturia, and daytime frequency. He was on intensive phase of antitubercular therapy for pulmonary tuberculosis. The left flank was tender on examination. Urine microscopy showed pyuria and hematuria. The serum creatinine was 1.82 mg%. Ultrasound showed a bulky left kidney with moderate hydroureteronephrosis. A left percutaneous nephrostomy was placed. He became afebrile and serum creatinine normalized after 48 h. The nephrostogram obtained subsequently showed central pooling of contrast in the excavated area [Figure 1, white arrow] in the region of interpole papilla giving “egg-in-a-cup” appearance characteristic of papillary necrosis [Figure 1].

Figure 1

Left nephrostogram showing persistent focal narrowing in the proximal ureter (black arrow) with proximal hydroureteronephrosis. Central pooling of contrast is seen in interpole medulla (white arrow) giving the egg-in-a cup appearance

DISCUSSION

Kidneys have dual circulation with cortex and medullary components.[1] Blood flow through the cortex is rapid and abundant while medullary flow is relatively slow.[1] Hypertonic interstitium and peculiar blood supply predispose medullary papillae to ischemic necrosis.[2] Pathologic conditions affecting vessels predispose to the papillary necrosis. Common causes are diabetes, analgesic overuse, sickle cell anemia, pyelonephritis, tuberculosis, and urinary tract obstruction.[23] Rifampicin therapy as uncommon cause of papillary necrosis has also been described.[24]

Papillary necrosis can be medullary or papillary type.[2] Medullary form is due to central necrosis at the tip of pyramid creating a round or oval cavity. Papillary form is due to necrosis of the larger part of papilla that starts separating in the region of the fornix.[2] Medullary form of papillary necrosis appears as “egg-in-cup” on contrast studies due to central pooling of contrast. Papillary type appears as signet ring sign due to filling of the whole of calyx and central triangular defect due to a sloughed papilla. In our patient, the infected hydronephrosis, rifampicin therapy for pulmonary tuberculosis, and urinary tuberculosis could be the predisposing factors for ischemic necrosis of the central part of papilla leading to medullary type of papillary necrosis.