NPH Surgery And Help

Cerebrospinal fluid shunts, commonly molded from silicone tubing, are susceptible to failure.  In fact, 30-40% of cerebrospinal fluid shunts malfunction after primary placement in the adult population.  Such malfunctions, while often benign, require additional hospitalizations and revision surgery.  For obvious reasons, this places the patient at risk.  Therefore, the maintenance of cerebrospinal fluid shunt patency is essential to patient wellness.

Presently, patients with a malfunctioning shunt undergo revision surgery to reestablish flow through the occluded shunt system.  In the adult population, this often requires removal of the shunt catheter from the abdominal compartment, resection of the distal 3-4 cm of catheter, and relocation of the residual catheter within the abdomen.  As stated above, the procedure and the inpatient hospitalization have associated risks and morbidity.

The majority of shunt malfunctions in the adult population are the direct result of an occlusion at the distal shunt catheter orifice (outlet).  The distal catheter tip, often located in the peritoneal cavity, is susceptible to blockage by fat (omental) or proteinaceous debris.  Also, the distal catheter may be lodged between bowel loops or between a segment of bowel and the walls of the abdominal cavity.  The distal catheter may lie within an intra-abdominal fluid pocket as well.  Any potential increase in outflow resistance may result in slowed CSF flow or florid obstruction of the shunt system.

In conjunction with a general surgery colleague, I have developed an implantable device which serves to secure the distal (peritoneal) catheter in a location free of potentially obstructive substrate (bowel, omental fat and fluid-filled pockets).  The device is composed of a circumferential cuff through which the shunt catheter traverses, and flanges.  The inner diameter of the cuff approximates the outer diameter of the CSF shunt distal catheter.  This will guarantee a snug, secure fit between the cuff and the shunt catheter while concomitantly preserving CSF flow within the catheter lumen.  Flanges are affixed to the circumferential cuff.  The flanges function to anchor the device to the target tissue or anatomic structure at the selected site.

The target anatomic structure is the falciform ligament.  The falciform ligament is a reflection of peritoneum that courses from the anterior abdominal wall to the liver (and in fact divides the liver into right and left lobes) in the sagittal plane.  The ligament is first fenestrated and the catheter (coursing through the securement device) then guided through the created fenestration.  The distal catheter tip will ultimately lie on the right lobe of the liver, free of potentially obstructive material.  This may transitively reduce the incidence of shunt malfunction as the distal catheter tip is less susceptible to blockage.

There is also a need for a method to implant the device, in particular, a minimally-invasive method that does not promote formation of scars and intra-abdominal adhesions, which are potential etiologies of shunt catheter malfunction.  The described device is implanted laparoscopically during primary shunt placement or revision procedures.

Laparoscopic implantation of the distal limb of the CSF shunt catheter system may reduce the incidence of shunt malfunction by optimizing catheter placement in a region free of potentially obstructive tissue or debris.  However, the conferred benefit is likely temporary.  Peristaltic motion and bodily movement promote catheter migration into less favorable positions within the abdominal cavity.  The catheter may become sequestered within loops of bowel and mesenteric fat or within a fluid pocket with locally elevated hydrostatic pressure.  By either, CSF outflow resistance is increased resulting in shunt malfunction.  It is much less often the case that the distal catheter tip is physically plugged with proteinaceous fat or debris.  In fact, this is rarely observed intra-operatively during distal revision surgical procedures.  During the vast majority of such procedures, the surgeon removes the distal catheter from the abdominal cavity only to find a functioning shunt system evidenced by CSF egress from the catheter tip.  Several centimeters of distal catheter are cut from the tip and the catheter is again placed into the abdominal cavity.  Whether this is performed laparoscopically or another technique is irrelevant, because the root problem of catheter migration has not been addressed.

The implantable device solves this problem by providing fixation of the distal shunt catheter to an anatomic structure, which suspends it in a site free of potentially obstructive soft tissue, fat, proteinaceous debris, intra-abdominal fluid pockets and intra-abdominal adhesions.

A number of advantages become evident:

• by potentially reducing the incidence of shunt malfunctions, the device may reduce the number of surgical revision procedures necessary, translating into a reduction of surgical morbidity and cost
• the device is easily implanted either at the time of initial surgery or during a revision procedure
• the device is preferably implanted laparoscopically. This method minimizes intra-abdominal adhesion formation associated with open abdominal shunt catheter surgery
• as the device is externally coupled to the distal shunt catheter, there are no intra-luminal components capable of causing a shunt malfunction and(e) the device is not subject to malfunction as caused by accumulation of proteinaceous debris and/or fat.