CT-guided percutaneous nephrostomy in an obstructed pelvic pancake kidney: a report of a novel transiliopsoas approach

Abstract

Pancake kidney is a rare renal fusion anomaly with increased risk of complications, such as stone disease and infections, due to altered urodynamics. Image-guided (ultrasonography and fluoroscopy) percutaneous nephrostomy (PCN) is performed to decompress an obstructed pancake kidney. However, routine image guidance may be unable to provide a suitable access in complex clinical scenarios. The approach for PCN in a low-lying fused kidney is difficult due to a limited safe posterior retroperitoneal paraspinal route, and anterior transperitoneal approach poses risks of urine leak and peritonitis. We report a case of an obstructed pancake kidney managed by CT-guided PCN through a transiliopsoas approach.

Background

Congenital fusion anomalies of the kidney occur during embryogenesis.¹ They usually remain in an ectopic position since the ascent to normal position is prevented by retroperitoneal structures. Congenital fusion anomalies of the kidney can be divided into two types: partial (horseshoe kidney and crossed-fused ectopia) and complete (pancake kidney). Pancake kidney is a rare variant with less than 30 cases described in the literature¹ wherein there is an absence of a renal capsule and fused upper and lower poles. They are typically located anterior to the aorta. Renal fusion anomalies can lead to a variety of complications, such as stone disease, infections and a variety of both benign and malignant tumours.^{1 2}

Percutaneous nephrostomy (PCN) plays a pivotal role in therapeutic management of obstructed kidneys whereby the upper urinary diversion and decompression of the renal collecting system is achieved. Since the description of trocar nephrostomy by Goodwin et al,³ several direct and wire-guided (Seldinger) methods of PCN tube placement have been described in the scientific literature.^{4 5} Routinely, a retroperitoneal approach is performed which is safe and effective. However, the standard route for accessing the pelvicalyceal system safely is often not possible in case of anomalous kidneys. In this case report, we present a case of pelvic pancake kidney presenting with pyonephrosis and managed by left-sided PCN under CT guidance through iliopsoas approach.

Case presentation

A 20-year-old male patient presented to the emergency department of our hospital with a history of haematuria, fever and vomiting for 2 days. The patient had a history of episodes of mild lower abdominal pain treated by over-the-counter pain medications. Physical examination was unremarkable. Initial laboratory investigations revealed leucocytosis (22.9×10⁹/L). Urine analysis was positive for pus and red blood cells. An admitting diagnosis of urinary tract infection (UTI) was made and empirical antibiotics were started. On further investigation, the serum creatinine and blood urea were 1.3 mg/dL and 56 mg/dL, respectively. An abdominal ultrasonography (USG) showed an ectopic kidney in the pelvis with hydronephrosis and internal echoes suggestive of pyonephrosis. No kidneys were seen in the bilateral renal fossae.

On CT urography (figure 1A,B), a single mass of renal tissue was seen in the midline of pelvis representing fused bilateral kidneys with communicating pelvicalyceal systems. There was pelvi–ureteric junction obstruction with disproportionate dilatation of renal pelvis with multiple secondary calculi and debris. The patient was referred to our interventional radiology facility for PCN. On USG screening, an optimal retroperitoneal approach to access the pyonephrotic kidney could not be obtained due to its location deep in the pelvis. A transperitoneal puncture was possible but was avoided due to the risk of peritonitis that may arise due to urine leak. Since the kidney and calyces were close to the left iliopsoas muscle, a transiliopsoas approach was planned under CT guidance (figure 1B). With the patient in supine position, the skin entry point and the route through the muscle was planned on the preliminary CT scan images to avoid the external and internal iliac vessels and the peritoneum. After obtaining asepsis, the renal system calyx was punctured through the iliopsoas using an 18G, 15 cm long, diamond-tipped two-part needle under local anaesthesia (figure 2). Subsequently, the tract was dilated using the Seldinger technique. Finally, an 8F pigtail catheter was inserted over an extra stiff guide wire and fixed with sutures. Pus was seen draining out and the pigtail catheter was connected to a collecting bag. USG (figure 3A) and nephrostogram (figure 3B) confirmed the position of the catheter without any leak. The patient improved symptomatically and was discharged. Later, the patient underwent open Fenger-plasty for pelvi–ureteric junction obstruction and nephroscopic stone retrieval.

Figure 1.

(A) Axial CT scan shows a single mass of renal tissue in the midline of pelvis representing bilateral fused kidneys (arrows) with communicating and dilated pelvicalyceal systems (asterisk). (B) A lower section of axial CT scan shows the planned route for a calyceal puncture (white arrow).

Figure 2.

Axial CT image of the pelvis shows the puncture needle passing through the left iliopsoas muscle (white arrow) and puncturing calyx (black arrow). Calculus is seen in the calyx (arrowhead).

Figure 3.

(A) Ultrasonography image shows pigtail catheter in the lower pole calyx of the left system (white arrows). (B) Nephrostogram shows pigtail catheter in situ with the opacification of the calyces (black arrow).

Treatment

The patient underwent open Fenger-plasty for pelvi–ureteric junction obstruction and nephroscopic stone retrieval.

Outcome and follow-up

A significant amount of pus was drained following the PCN. The patient’s lower abdominal pain and fever resolved within 24 hours. He was discharged on the second day and was advised oral antibiotics for 1 week and follow-up in urology outpatient department. After a month, the patient underwent open Fenger-plasty for pelvi–ureteric junction obstruction and nephroscopic stone retrieval. Currently, the patient is asymptomatic and doing fine.

Discussion

Pancake kidney is a very rare type of fused renal ectopia.¹ The embryological basis for pancake kidney is complete medial fusion of each metanephric mass in the pelvis during early ascent. Each kidney has its own collecting system and anteriorly placed short ureters entering the bladder normally. Retroperitoneal structures prevent the ascent of fused kidneys. Looney and Dodd were the first to describe the pancake kidney.⁶ The pancake kidney is more common in men and is often associated with other genitourinary and vertebral anomalies.⁷ Review of the literature unfolds several cases of fused pelvic kidneys with concomitant anomalies, such as Tetralogy of Fallot, sacral agenesis and caudal regression, failure of testicular descent, spina bifida and anal abnormalities.^{1 2}

Since pancake kidney is predisposed to recurrent UTIs and stone formation, imaging has a vital role not only in the diagnosis of this rare entity but also in early detection and management of complications. Early diagnosis of complications can prevent permanent renal damage. USG and CT scan are sensitive modalities not only for the detection and evaluation of pancake kidney anomaly but also for the exclusion of concomitant anomalies.

PCN was first described by Goodwin et al in 1955 as a blind puncture technique.³ USG later became the preferred guidance modality for PCN since it has the advantage of avoidance of radiation exposure and use of contrast agents and is ideal in pregnant patients and children. However, USG has limitations as a guiding modality in obese patients and in patients with undilated renal calyces. CT guidance for PCN was first introduced by Haaga et al in 1977 and has better anatomic mapping, equal precision for dilated and undilated calyces, and lesser complications.⁸

Routinely, a retroperitoneal approach is used for PCN since it is the safest, has a shorter route and less chance of bowel injury.⁹ The hypovascular plane in the watershed region between anterior and posterior renal artery divisions also reduces the bleeding risk. Routine retroperitoneal approach is frequently not possible in a fused pelvic kidney due to a limited safe paraspinal route. There is one case report in the literature of PCN placement in obstructed pancake kidney through retroperitoneal approach.¹⁰ Anterior transperitoneal approach is not preferred since it poses a risk for urine leak and peritonitis.¹¹ Also, the nearby bowel and vessels obviate the use of this approach.

There are reports of pelvic abscess drained through transiliopsoas route.¹² This route is suited for percutaneous biopsy of lesions lying medial to iliopsoas muscle.¹³ Soft-tissue masses along the lateral pelvic sidewall, adnexal masses and common iliac nodes located posterior to the iliac vessels can also be sampled with this technique.¹³ This approach has some added advantages, such as minimal risk of bowel injury and no peritoneal leak, stability of the catheter across iliopsoas muscle and better patient comfort.^{13 14} However, there are no reports in the literature describing transiliopsoas approach for PCN.

In the case presented here, the transperitoneal approach, although was possible, was avoided to prevent complications. Using a transiliopsoas approach, we could safely perform a PCN to drain the infected renal system without risks of peritoneal leak or bowel injury.

In conclusion, we describe a novel approach, that is, transiliopsoas route to perform a PCN in an obstructed pelvic pancake kidney. This approach may be safely used in situations where a standard retroperitoneal approach is not possible.

Learning points.

• Pancake kidney is a rare variant wherein there is an absence of a renal capsule and fused upper and lower pole and can lead to a variety of complications, such as stone disease, infections and a variety of both benign and malignant tumours.

• Percutaneous nephrostomy (PCN) plays a pivotal role in therapeutic management of obstructed kidneys whereby the upper urinary diversion and decompression of the renal collecting system is achieved.

• Standard retroperitoneal route for accessing the pelvicalyceal system safely is often not possible in case of anomalous kidneys.

• Transiliopsoas route is a novel approach to perform a PCN in an obstructed pelvic pancake kidney.