Low anterior resection adjacent to a pancake kidney: case report

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Pancake kidney is a very rare congenital renal anomaly consisting of a lobulated pelvic renal mass with fusion of both upper and lower renal poles, typically drained by two separate collecting systems.1 We present a case of a successfully resected rectosigmoid cancer adherent to a solitary pelvic pancake kidney.
A 59‐year‐old previously well man presented in July 2014 with an obstructing rectosigmoid tumour. Staging demonstrated a large colorectal adenocarcinoma with three liver metastases (T3N0M1a). Initial management included defunctioning transverse loop colostomy and neoadjuvant chemotherapy. Preoperative computed tomography (CT) angiogram revealed a single completely fused pelvic kidney equipped with separate collecting systems and ureters, which descended to normally located bilateral vesicoureteric junctions. The right renal moiety was supplied by four arteries, which took origin from the aortic bifurcation: two penetrating the superior aspect of the kidney and the other two coursing anteriorly into the hilum; the left moiety was supplied by two smaller arteries, from the left common iliac artery in the superior aspect and from the left internal iliac artery into the hilum (Figs 1). Venous drainage was by a single large vein on the right, which joined the left common iliac vein, and by three smaller veins on the left draining into the left common and the right and left internal iliac veins. A normal inferior mesenteric artery passed anteriorly to all these structures and towards the sigmoid tumour.
Open low anterior resection was undertaken in conjunction with a urologist. A ureteric catheter was passed up the right ureter but it was not possible to pass a catheter up the left ureter due to angulation. The inferior mesenteric artery was identified and divided and the sigmoid colon peeled off the anterior part of the kidney. A segment of Gerota's fascia was resected en bloc with the colon at the site of the tumour where there appeared to be fusion of the tumour to ensure a clear resection margin. The rectum was dissected in the mesorectal plane within the pelvis below the kidney and divided. The rectum was then elevated and the superior and inferior dissection planes connected. The right ureter was identified but it was impossible to identify the left ureter despite easy identification on the CT reconstruction (Fig. 1). Intravenous injection of methylene blue was used to confirm absence of ureteric injury. An end colostomy was created; an anastomosis would have been under tension due to anterior angulation from the pancake kidney despite full mobilization of the splenic flexure. Histopathology confirmed clear resection margins with no tumour in zero out of 11 resected lymph nodes. Post‐operative recovery was uneventful, renal function remained normal. The patient was discharged home on day 9 and is currently awaiting planned resection of liver metastases.
Pancake, discoid or cake kidney synonymously refers to an anomaly in which the entire renal parenchyma is fused in one pelvic mass without intervening septum.2 In an even rarer anomaly only one ureter may be present.3 The differential diagnosis includes the more well‐known horseshoe kidney, recognized in approximately one in 700 autopsies. However, the pancake kidney is exceedingly rare and its exact incidence is unknown.1 Renal fusion anomalies may be seen in a number of congenital syndromes and are associated with a slightly increased risk of renal primary renal malignancies, injury, recurrent infections and calculi.2 Given its rarity, no specific anomalous associations have been described for the pancake kidney. While usually asymptomatic, the pelvic kidney presents a great technical challenge for surgical approaches to the adjacent structures (e.g. repair of vascular aneurysms5) as well as for targeted radiotherapy.
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