Data from Oregon Health Sciences University. In this retrospective institutional series, about 33% of shunts failed in the first year. Beyond the first year, the annual risk of failure dropped to about 5%. Half of all shunt lasted longer than 6 years.
The Shunt Design Trial compared two novel (and relatively expensive) shunt valves with the standard differential pressure valve. The newer valves were both designed to prevent excessive CSF drainage. There were NO differences in survival among the 3 arms of the study at 1 and 2 years, although the patterns of failure differed between the Orbis-Sigma and the other 2 arms. [Drake JM. Randomized trial of cerebrospinal fluid shunt valve design in pediatric hydrocephalus. Neurosurgery 1998;48:294-303.]
“Bioglide” is a novel surface treatment for the silastic material used in fabrication of CSF shunts developed by Medtronic. The initial intention was to reduce infection risk, but early after its introduction there was hope that the surface treatment would reduce tissue adherence and proximal obstruction as well. These hypotheses have never been tested in a scientific fashion.
The closing pressure of the Codman Medos valve can be adjusted transcutaneously with a computer-driven magnetic device. In theory this valve allows greater flexibility in adjustment of valve properties to suit individual patient requirements, but it has not been shown to reduce the need for reoperation in randomly selected patients.
The Shunt Design Trial demonstrated the importance of ventricular catheter position as a determinant of risk of shunt failure. [Tuli S. Change in ventricular size and effect of ventricular catheter placement in pediatric patients with shunted hydrocephalus. Neurosurgery 1999;45:1329-33.] Several technologies assist the surgeon in optimizing ventricular catheter position. Illustrated is a 1.2mm endoscope that actually fits inside the shunt catheter and peeks out through the tip of the ventricular end. The surgeon can use real-time images of ventricular anatomy to confirm proper placement. The efficacy of this technology is being tested in a multicenter, randomized, controlled trial, the Endoscopic Shunt Insertion Trial.
A view of the foramen of Monroe and a tuft of choroid plexus through an endoscope.
Intraoperative ultrasound can provide real-time guidance as the surgeon advances the ventricular catheter into position. Logistical obstacles limit the use of ultrasound at many institutions. The frontal horns of the lateral ventricles are very clear on this diagnostic study.
On this intraoperative study obtained through a coronal plane similar to the previous diagnostic image, the ventricles are outlined by asterisks, and the arrow marks the ventricular catheter.
Surgical navigation systems allow precise correlation of patient anatomy with computed tomographic (CT) scans and magnetic resonance (MR) images in the operating room. This technology can be used to guide ventricular catheter placement as well.
As the surgeon touches a spot in the surgical field, the navigation system places a cursor at the corresponding spot on the monitor image.
In 70 to 80% of technically suitable cases, CSF shunt failure can be managed by endoscopic third ventriculostomy (E3V) without replacement of the shunt.
E3V may be an option in the management of selected CSF shunt infections as well.
Patients with very small baseline ventricular volume and frequent episodes of CSF shunt failure are sometimes said to have “slit ventricle syndrome.” With aggressive management, CSF shunt removal can be accomplished for a significant fraction of such patients.
E3V creates a new pathway for drainage of CSF from the third ventricle into the space around the brainstem at the base of the brain, bypassing blockages in the aqueduct, fourth ventricle and its outlets.
An interior view of the third ventricle.
A surgical hole in the thin, translucent floor of the third ventricle.
The surgeon uses a balloon to enlarge the hole.
The endoscope has been passed through the hole, and the basilar artery is in view.
Unfortunately, E3V has not proved to be a cure for hydrocephalus in many instances. In the aggregate, E3V is no better than CSF shunt insertion in minimizing patient trips to the operating room.
Based on laboratory animal experimentation, antenatal myelomeningocele repair was originally attempted as a measure to prevent injury to the exposed spinal cord by toxic amniotic fluid. The hope that antenatal repair would protect lower extremity function has not been realized in the initial experiences at Vanderbilt and the Children’s Hospital of Philadelphia. But investigators made the unexpected observation that the fetal Chiari malformation regresses after antenatal repair and that infants subsequently seem need CSF shunt insertion less frequently than expected.
The hypothesis that antenatal myelomeningocele repair reduces the need for subsequent treatment of hydrocephalus will be tested in a multicenter, prospective, randomized trial, the Myelomeningocele Repair Clinical Trial.
The posterior fossa, the compartment of the cranial cavity that houses the brainstem and the cerebellum (the “hindbrain”), is abnormally small in patients with myelomeningocele. It cannot accommodate the brain structures that belong in it. As the brain grows, the bottom of the brain stem and an adjacent portion of the cerebellum are pushed out of the head into the cervical spine. This displacement of the cerebellum (and the brainstem) is called the Chiari malformation. The Chiari malformation type 2 is the pattern of deformity that occurs with myleomeningocele.
Displacement of the caudal brainstem and cerebellum into the cervical spine.
Syringomyelia is a cavitation of the spinal cord caused by disturbances of CSF circulation in the spine. It can lead to various neurological disabilities, including loss of sensation, weakness, paralysis, muscle atrophy, bladder dysfunction, and scoliosis. Spinal arachnoid cysts are relatively common among patients with myelomeningocele and can cause neurological disabilities by spinal cord compression. Diastematomyelia is a birth defect involving the spinal cord. It is a rather frequent fellow traveler with myelomeningocele, in perhaps 20% of cases, and it can cause spinal cord tethering and progressive neurological problems if it escapes recognition. Dermoid cyst is another fellow traveler. It may arise as an associated birth defect, or it can occur as a complication of myelomeningocele repair. Through whatever process, a small patch of skin becomes displaced among the neural tissues in the spinal canal. The skin survives and proliferates to form the cyst membrane, and skin debris collects inside. Dermoid cysts are usually incidental findings in the investigation of other problems; they seldom cause symptoms on their own. Normally the spinal cord dangles free in the spinal canal, and with normal movements the spinal cord slips up and down within the spinal canal. When the spinal canal is anchored at the bottom by a birth defect or by scar tissue, spinal cord “tethering” has occurred. Tethering can cause mechanical damage to the segments of the spinal cord immediately above, leading to progressive neurological disability. ALL patients with myelomeningocele have tethering of the spinal cord at the site of the repair, but the lifetime risk of clinical problems from tethering is only 30 – 40%.
The asterisk marks a syrinx cavity in this MR scan of a child with myelomeningocele.
This teenager had been followed for many years with an untreated syrinx until she appeared at her annual clinic visit with a withered hand. Treatment of the syrinx did not restore her lost function. Periodic monitoring of grip strength can detect mischief in the spinal cord in time for treatment, before major functional disability has developed. [Aronin PA. Value of dynamometry in assessing upper extremity function in children with myelomeningocele. Pediatr Neurosurg 1995;23:7-12.]
ALL patients with myelomeningocle have spinal cord tethering at the site of the repair. The clinical challenge is to determine whether tethering is to blame for nonspecific symptoms and to judge whether surgical intervention will more likely help or hurt.
The multidisciplinary Spina Bifida Clinic team at St Christopher’s Hospital for Children.
An Overview of
Joseph H Piatt, Jr, MD, FAAP
Spina Bifida and Neurosurgery
¶ better CSF shunts
¶ better CSF shunt surgery
¶ removal of CSF shunts
¶ avoidance of CSF shunts
¶ Chiari malformation type
¶ spinal cord complications
¶ 85 – 90% prevalence among MM pts
¶ shunt failure: acute or insidious
¶ > 1 / 3 fail in first year
¶ 5 – 10% infection rate per operation
¶ 1 – 2% mortality (!) per failure
¶ exacerbation of CM2 / syringomyelia
Better CSF Shunts
¶ the Shunt Design Trial
¶ programmable valves
Shaveless CSF Shunt Surgery
¶ Horgan MA, Piatt JH Jr.
Shaving of the scalp may
increase the rate of
infection in CSF shunt
¶ Winston KR. Hair and
Removal of CSF Shunts:
¶ If it ain’t broke, don’t fix it.
¶ E3V for CSF shunt failure
• “elective” for slit ventricle
¶ E3V for CSF shunt infection
Management of Shunt Failure
¶ Cinalli G. The role of endoscopic third
ventriculostomy in the management of shunt
malfunction. Neurosurgery 1998;43:1323-7.
¶ Teo C. Management of hydrocephalus by
endoscopic third ventriculostomy in patients
with myelomeningocele. Pediatr Neurosurg
Management of Shunt Infection
¶ Jones R. Third ventriculostomy for shunt
infections in children. Neurosurgery
¶ Fukuhara T. Risk factors for failure of
endoscopic third ventriculostomy for
obstructive hydrocephalus. Neurosurgery
Management of “Slit Ventricle
Syndrome” with E3V
¶ Baskin J. Ventricular shunt removal: the
ultimate treatment of the slit ventricle
syndrome. J Neurosurg 1998;88:478-84.
¶ Reddy, K. Slit ventricle syndrome with
aqueduct stenosis: third ventriculostomy as
definitive treatment. Neurosurgery
Spinal Cord Tethering
¶ progressive neurological deficits
¶ bladder dysfunction
¶ a diagnosis of exclusion
¶ surgical risks and benefits
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