Spontaneous knotting of peritoneal catheter: A report of an asymptomatic patient.

Dear Sir,

Ventriculo-peritoneal (VP) shunt remains the treatment of choice for most forms of hydrocephalus. The common abdominal complications include spontaneous extrusion of the peritoneal catheter, obstruction due to fibrous encasement, shunt migration, infection, and cerebrospinal fluid (CSF) fistulas.[1] In the present communication, we describe a case with spontaneous knot formation at the peritoneal end of a VP shunt with no shunt block and detected incidentally.

A 10-year-old boy, known case of Crouzon's syndrome, was shunted for congenital hydrocephalus 7 years back using Indian-made medium pressure Chhabra ventriculoperitoneal shunt.[1] Presently, the patient presented to us with a boil on his lower part of anterior chest wall [Figure 1]. Owing to its proximity to the shunt tract, the child was investigated for possible cellulitis of the shunt tract and shunt infection. There was no clinical evidence of shunt malfunction. Plain abdominal radiograph revealed a long peritoneal catheter, with a reef-knot, just proximal to its terminal end [Figures 2 and 3]. Plain computed tomography (CT) scan of head showed decompressed ventricular system, with normally placed ventricular shunt catheter [Figure 4].

Figure 1

Clinical picture of the patient showing a boil on anterior surface of chest wall, just near to palpable catheter

Figure 2

Plain radiograph of abdomen, showing peritoneal catheter with a knot at the distal end

Figure 3

Plain radiograph showing knotted peritoneal catheter, just 2 cm proximal to distal end

Figure 4

Plain CT scan of head showing well decompressed ventricles, with correctly placed ventricular catheter

As the boil on chest wall responded well to antiotics (oral cloxacillin 1500 mg/day in three divided doses), no intervention was thought necessary to correct the knot problem. The child is placed under regular follow-up.

Peritoneal catheter dysfunction is usually due to placement or migration of the catheter into the extra-peritoneal compartment, abdominal infection, adhesions around distal tip, and rarely migration of the catheter tip into abdominal or thoracic viscera.[2] Spontaneous knot formation in the peritoneal catheter is a rare occurrence and a few cases [Table 1] have been reported.[3-6] Except one reported case,[3] all had presented with malfunctioning shunt.

Table 1

Reported cases of peritoneal catheter knotting

The mechanism causing such complication remains a matter of conjecture. All authors have put forth the possible mechanisms, which are far from satisfactory.[56] Factors, which may play a role include:

Catheter characteristics—Length, diameter, elasticity of catheter material.

Abdominal cavity—capacity and configuration.

Direction of catheter movement.

Framing all these factors together indicate greater catheter length, less of catheter diameter, and highly elastic catheter material predispose to knot formation.[4] Further, increased abdominal volume and crowding of intra-abdominal contents may play a role.[4] The comparison made with the umbilical cord knotting is thought provoking, except for the absence of ball-chain construct or model, which may be compared to fetus.[6] Vigorous peristalsis, and sometimes, reverse peristalsis may add on to the predisposition to knot formation.[6]

Factors governing spontaneous knot formation were evaluated using jostled strings in an experimental model. Lengthy and flexible strings showed more probability of knot formation.[7] Duration of agitation has also been cited as the probable factor, which did not explain spontaneous knotting in case 2 [Table 1]. Above a critical string length, the probability of knotting at first increased sharply with length but then began to level off. Moreover, the confinement tends to restrict kinetic motion and reduces knotting.[67]

The probability of forming a composite knot rises significantly with the confinement. Other geometrical indicators such as writhe and chirality are also described.[8] In knot theory,[8] writhe is the total number of positive crossings minus the total number of negative crossings. Reidemeister move refers to one of three local moves on a link diagram. Each move operates on a small region of the diagram and is one of three types. The type I move is the only move that affects the writhe of the link, while the type III move is the only one which does not change the crossing number of the diagram. In the mathematical field of knot theory,[8] a chiral knot is a knot that is not equivalent to its mirror image. An oriented knot that is equivalent to its mirror image is an amphichiral knot. All knots described in the reported cases seem to be of chiral type. The terminal end of peritoneal catheter involvement for knot formation is common to all reported cases.

Conclusion

Spontaneous knotting of peritoneal catheter remains a rare cause of shunt malfunction. Preoperatively, such a complication may be diagnosed after obtaining plain abdominal radiograph. The normally functioning shunt may also develop knotting of peritoneal catheter, but the intervention is not warranted, till the patient is asymptomatic. Such patients should be regularly followed up.