The Pretzel Sign – an indicator of pre-peritoneal catheter location

Creating peritoneal access is an essential part of the peritoneal dialysis patient pathway. Here we present two cases of catheter insertion into the pre-peritoneal or retropubic space and describe characteristic imaging findings.

Case 1

A 58-year-old male with end-stage kidney disease underwent percutaneous peritoneal dialysis (PD) catheter insertion with local anaesthesia using the Seldinger technique (LAPD). At the time of the procedure, his body mass index (BMI) was 29. The procedure, conducted by a highly experienced operator was uneventful. The catheter was inserted easily and 60 ml saline was flushed in and drained out of the catheter with good flows. Subsequently, when dialysis was commenced, it was only possible to instil 500 ml of fluid before resistance was encountered and the patient experienced suprapubic discomfort. An abdominal X-ray was performed (Figure 1a) followed by computed tomography (CT) which confirmed the extra-peritoneal position of the catheter (Figure 1b). The catheter was then removed and subsequently reinserted laparoscopically. He successfully started PD and 3 months later received a kidney transplant.

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Figure 1.

(a) Plain abdominal X-ray showing the catheter tightly coiled in the midline at the level of the sacrum. (b) Computed tomography (CT) sagittal view showing distal end of the Tenckhoff catheter coiled in a pre-peritoneal position anterior to the urinary bladder and behind the transverse fascia. This potential anatomical space is called the retropubic or Retzius space. (c) Plain abdominal X-ray showing the catheter coiled in the midline near the insertion site, an intraunterine device is also visible. (d) Reconstruction of CT abdomen pelvis sagittal view showing catheter coiled in the supravesical position, anterior to the peritoneal cavity.

Case 2

A 45-year-old female underwent LAPD insertion. Her BMI was 20. The procedure was uneventful, in and out flow of 100 ml of saline was established. A week later she reported pain on draining in fluid. An abdominal X-ray was performed (Figure 1c). A departmental ultrasound scan suggested the catheter was intra-peritoneal. Subsequently, a CT scan delineated pre-peritoneal positioning (Figure 1d). The catheter was removed and laparoscopically reinserted. She was established on PD and received a kidney transplant 2 years later.

Discussion

The percutaneous Seldinger technique for PD catheter insertion is a safe and effective procedure with similar outcomes to surgical insertion. ¹ An early and rare complication of this technique is inadvertent malposition including pre-peritoneal insertion into the retropubic space. ²

These cases illustrate several learning points: in both cases, abdominal X-ray revealed the pig-tail portion of the catheter to be tightly coiled in the midline. We suggest that this characteristic appearance on X-ray should heighten suspicion of malposition and be called ‘The Pretzel Sign’. While high BMI/thick anterior abdominal wall is thought to be a risk factor for pre-peritoneal catheter insertion the second case in which the patient's BMI was 20 demonstrates that the risk of malposition is not confined to those with an elevated BMI.

In both patients, the combination of inability to instil large volumes of fluid and discomfort when doing so prompted further investigation. There is no consensus on the appropriate volume of fluid used to test hydraulic function after insertion, ³ we suggest that using small volumes (<500 ml) increases the chances of the pre-peritoneal position being unrecognised at the time of insertion. Additionally, when available, the routine use of real-time image guidance (ultrasound, fluoroscopy, or a combination of both) should reveal the coiling of a misplaced guidewire anterior to the peritoneum, alerting operators before catheter insertion.