Aqueductal stenosis

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Aqueductal stenosis
Gray734.png
Drawing of the ventricular system from Gray's Anatomy, with third and fourth ventricles and the aqueduct of Sylvius (cerebral aqueduct) labeled
Specialty Neurosurgery

Aqueductal stenosis is a narrowing of the aqueduct of Sylvius which blocks the flow of cerebrospinal fluid (CSF) in the ventricular system. Blockage of the aqueduct can lead to hydrocephalus, specifically as a common cause of congenital and/or obstructive hydrocephalus. [1] [2]

Contents

The aqueduct of Sylvius is the channel which connects the third ventricle to the fourth ventricle and is the narrowest part of the CSF pathway with a mean cross-sectional area of 0.5 mm2 in children and 0.8 mm2 in adults. [3] Because of its small size, the aqueduct is the most likely place for a blockage of CSF in the ventricular system. This blockage causes ventricle volume to increase because the CSF cannot flow out of the ventricles and cannot be effectively absorbed by the surrounding tissue of the ventricles. Increased volume of the ventricles will result in higher pressure within the ventricles, and cause higher pressure in the cortex from it being pushed into the skull. A person may have aqueductal stenosis for years without any symptoms, and a head trauma, hemorrhage, or infection could suddenly invoke those symptoms and worsen the blockage. [4]

Signs and symptoms

The enlarged skull of a person with hydrocephalus, which is a symptom of the excess CSF in the ventricular system. This may be caused by aqueductal stenosis, and in some cases, it is thought that hydrocephalus will cause aqueductal stenosis. 4948137341 1ccab41fda bHydrocephalic.jpg
The enlarged skull of a person with hydrocephalus, which is a symptom of the excess CSF in the ventricular system. This may be caused by aqueductal stenosis, and in some cases, it is thought that hydrocephalus will cause aqueductal stenosis.

Many of the signs and symptoms of aqueductal stenosis are similar to those of hydrocephalus. These typical symptoms include: headache, nausea and vomiting, cognitive difficulty, sleepiness, seizures, balance and gait disturbances, visual abnormalities, and incontinence. [5]

Signs of aqueductal stenosis other than those mentioned in “Causes of stenosis” include detection of an enlarged lateral and third ventricle in conjunction with a smaller fourth ventricle. This variation in ventricle size is indicative of a blockage in the aqueduct because it lies between the third and fourth ventricles. Another sign of stenosis is deformation of the midbrain, which can be severe. This is caused by the pressure gradient formed from a blockage in the aqueduct. [3]

Causes

Tumor compression

In cases of aqueductal stenosis caused by tumor compression, a brain tumor in the region of the midbrain forms. More specific anatomically, a tumor forms in the pineal region which is dorsal to the midbrain and is level with the aqueduct of Sylvius. [2] As the tumor grows and expands, it compresses the aqueduct to eventually obstruct it.

Narrow aqueduct

A naturally narrow aqueduct allows for it to be more easily obstructed. Narrow aqueducts have no unusual tissue characteristics, and ventricles are lined with normal epithelial cells. Narrowing can be a defect from birth that results in congenital aqueductal stenosis. Developmental errors that could result in this defect include abnormal folding of the neural plate which causes the neural tube to be narrowed from birth. [3]

Forking

Forking refers to an aqueduct that has become split into multiple, separate channels as a result of incomplete fusion of the median fissure. [3] These channels may connect back together to form a single aqueduct again, or they may abruptly stop and form a dead-end. Both of these deformations disrupt the laminar flow of CSF through the ventricular system, causing the force by the aqueduct on its surroundings to be lower than the compressive force being applied to the aqueduct. This greater compressive force could effectively stop the flow of CSF if the aqueduct closes due to the force. [8]

Septum formation

Formation of a septum implies that through gliosis, a membrane of glial cells has developed across the aqueduct. This abnormal membrane most commonly forms at the lower and distal portion of the aqueduct, and completely obstructs the canal. This barricade causes the portion of the aqueduct above it to become dilated with the excess CSF which in turn applies more pressure to the cells in this upper part. [3] This increased pressure amplifies the effects of gliosis, as described in the next section.

Gliosis

With this condition, the aqueduct begins as partially blocked. To compensate for the partial blockage and increase the CSF flow to normal rates, the pressure in the third ventricle is increased thereby also increasing the velocity of the CSF. This in turn creates more shear stress in the aqueduct, causing more damage to the epithelial cells lining the ventricle, and resulting in gliosis and a proliferation of glial cells. This increased number of cells thus causes the blockage to worsen, necessitating more pressure and velocity, and continuing the cycle of gliosis. [3]

Other medical conditions

A genetic disorder called “Brickers-Adams-Edwards syndrome” or “X-linked hydrocephalus” has been discovered that leads to aqueductal stenosis. This disease is transmitted from mother to son. This disorder is caused by a point mutation in the gene for neural cell adhesion. Most males born with this have severe hydrocephalus, adducted thumbs, spastic motions, and intellectual problems. Females with this defect may have adducted thumbs or subnormal intelligence. [3]

Bacterial meningitis can also result in gliotic blockage of the aqueduct. In utero infection or infection during infancy could both result in glial cell build-up to make an obstruction. [3]

Connection to hydrocephalus

It is generally considered that aqueductal stenosis is a precursor to non-communicating hydrocephalus, as the blockage of the aqueduct would result in the accumulation of CSF seen in hydrocephalus. However, some studies also argue that cases of aqueductal stenosis not involving a brain tumor are actually a result of communicating hydrocephalus, rather than a cause of it. When a patient has communicating hydrocephalus, the lateral ventricles and medial parts of the temporal lobes expand and compress the aqueduct. As a result, the pressure within the fourth ventricle drops and causes the aqueduct to close more tightly. This in effect could make aqueductal stenosis a byproduct of hydrocephalus. [8] It is estimated that only 25% of males with X-linked hydrocephalus have aqueductal stenosis, which supports the theory that the stenosis may sometimes be a symptom of hydrocephalus. [3]

Diagnosis

Ventricular system with third ventricle highlighted red Third ventricle small.gif
Ventricular system with third ventricle highlighted red
Ventricular system with fourth ventricle highlighted red Fourth ventricle small.gif
Ventricular system with fourth ventricle highlighted red

CT scan

CT scans are used to visualize the structure of the inside of the body without needing to make any incision. For the purposes of diagnosis aqueductal stenosis, a scan is performed on a patient's brain. Images showing an enlarged third ventricle along with a normally sized fourth ventricle (in a lateral view) is generally considered to be an indication of aqueductal stenosis, but this is still only presumption. [2] [3] CT scans are typically used after a shunt treatment in order to analyze ventricle size and determine if the device is working. One complication associated with this analysis (as well as when analyzed by MRI) is that images of a small ventricle do not always correspond with a functioning shunt as a small ventricle would seem to imply. The reduced ventricle size can sometimes be due to a condition called slit ventricle syndrome. [9] Another complication is that if the stenosis is caused by tumor compression, there is a possibility that the scan will miss detecting small brainstem tumors. [3]

MRI imaging

MRI is considered the best method of detecting aqueductal stenosis because it can visualize the entire length of the aqueduct, can clearly depict tumors, and can show ventricle enlargement or other deformations. [2] [3] It is helpful in determining the extent of the aqueductal obstruction, particularly when multiple masses or lesions are present, and thereby aids in determining the most appropriate treatment method (i.e. surgery, shunt, or ETV). [3] When constructive interference in steady state (CISS) or fast imaging employing steady-state acquisition (FIESTA) sequence are used, subtle abnormalities or partial obstructions in the aqueduct can be depicted in the MRI. [1] For example, CISS can be used to determine if a thin membrane interfering with CSF flow is present. [10]

Other

Phase contrast-MRI is an imaging method that is more sensitive than MRI for analysis of the pulsatile CSF flow in the ventricular system. This method takes multiple images of the ventricles within one cardiac cycle to measure the flow of CSF running past the area of acquisition. If no flow is seen, this is a reliable diagnosis of aqueductal stenosis as it implies that there is a blockage of CSF. [3]

Ultrasonography can be used in utero to diagnose aqueductal stenosis by showing dilation of the lateral and third ventricles. A retrospective study found that diagnosis can be made as early as 19 weeks of gestation, and that on average diagnosis is made at 33 weeks.

Treatments

The general purpose of the following treatment methods is to divert the flow of CSF from the blocked aqueduct, which is causing the buildup of CSF, and allow the flow to continue. Another goal of these treatments is to reduce the stress within the ventricles. Studies have not shown that either of the following treatments results in a higher IQ of the patient, and there is no statistical difference in a patient's quality of life based on treatment method. [4] The following treatment methods are not used for aqueductal stenosis caused by tumor compression; if the obstruction is a direct result of tumor compression, CSF flow may be normalized by the surgical removal of the tumor.

Extracranial shunt

An extracranial shunt is essentially a sturdy tube with a catheter on one end to drain the third ventricle. The shunt also has a valve which serves to maintain one-way flow of the CSF and regulates the flow rate. The end with the catheter is placed in the third ventricle to drain the excess CSF and the other end is placed in the peritoneal cavity or atrium of the heart (making it a ventriculoperitoneal or ventriculoatrial shunt, respectively). The excess CSF which is diverted to a cavity is then reabsorbed by the surrounding tissue where it is drained to.

The procedure to insert this device is a technically straightforward endoscopic surgery with a low mortality rate (essentially 0% mortality since the 1970s). [11] If the shunt has an adjustable valve the current method of setting the valve pressure is to choose one setting, observe the patient to see if CSF flow improves and the symptoms lessen over time, and adjust the pressure setting as needed if improvement isn't seen. For example, if there is not enough CSF flow, another surgery is performed to lower the valve pressure so that less force needs to be applied to open the valve and thereby drain more CSF. [9]

This treatment method has several possible problems with it (with a 50% failure rate in 2 years), [4] and unfortunately shunt malfunctions and associated complications cause a death rate of 1.2% per year. [11] Problems which can necessitate a secondary surgery to fix them include: mechanical failure, incorrect catheter size, inappropriate valve drainage pressure, and infection. [12]

Endoscopic third ventriculostomy

An endoscopic third ventriculostomy (ETV) is a procedure where an incision is made in the bottom of the third ventricle to make a drainage point for CSF to flow out of. The procedure is minimally invasive and is performed endoscopically. The goal in the surgery is to create a path for communication between the third ventricle and the subarachnoid space outside the brain for reabsorption of CSF. ETV has a higher failure rate than shunting during the first 3 postoperative months, but after this time the risk of failure progressively drops to become half as high as the failure risk for shunting. [3]

This treatment does not place a foreign body into the patient so there is a much lower risk of infection as compared to a shunt procedure. Along with not implanting a device, this procedure avoids mechanical issues like disconnection, over or underdrainage, and valve dysfunction. [3] The surgery begins by entering the right or left lateral ventricle endoscopically through a burr hole. The third ventricle is identified and entered as well, and an incision is made in the floor of the ventricle and enlarged as necessary with tools such as forceps or Fogarty catheters. If a membrane prevents CSF flow between the ventricle and the subarachnoid space, then an incision is made in the membrane as well. [4] Ideally this procedure can be performed near the midline of the brain with minimal side-to-side motions of the endoscope so as to not tear tissues and cause further complications. [10]

Research has found that this procedure has a 75% success rate, [13] that 72% of ETV surgeries are still correctly functioning after 15 years, and that patients have shorter hospital stays recovering as compared to shunting. [4] If the procedure does not successfully cure the aqueductal stenosis, a second surgery can be performed to enlarge the incision or implant a shunt. Problems that can lead to these failures and require additional surgery include the stoma becoming closed or a new membrane forming across the stoma over time. Currently there is no universal decision about whether this should be performed in children, as infants have a higher tendency to have a membrane form over the incision which means that an additional surgery would have to be performed. [4]

Related Research Articles

<span class="mw-page-title-main">Cerebrospinal fluid</span> Clear, colorless bodily fluid found in the brain and spinal cord

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.

<span class="mw-page-title-main">Idiopathic intracranial hypertension</span> Medical condition

Idiopathic intracranial hypertension (IIH), previously known as pseudotumor cerebri and benign intracranial hypertension, is a condition characterized by increased intracranial pressure without a detectable cause. The main symptoms are headache, vision problems, ringing in the ears, and shoulder pain. Complications may include vision loss.

<span class="mw-page-title-main">Syringomyelia</span> Disorder in which a cyst forms in the spinal cord

Syringomyelia is a generic term referring to a disorder in which a cyst or cavity forms within the spinal cord. Often, syringomyelia is used as a generic term before an etiology is determined. This cyst, called a syrinx, can expand and elongate over time, destroying the spinal cord. The damage may result in loss of feeling, paralysis, weakness, and stiffness in the back, shoulders, and extremities. Syringomyelia may also cause a loss of the ability to feel extremes of hot or cold, especially in the hands. It may also lead to a cape-like bilateral loss of pain and temperature sensation along the upper chest and arms. The combination of symptoms varies from one patient to another depending on the location of the syrinx within the spinal cord, as well as its extent.

<span class="mw-page-title-main">Hydrocephalus</span> Abnormal increase in cerebrospinal fluid in the ventricles of the brain

Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary incontinence, personality changes, or mental impairment. In babies, it may be seen as a rapid increase in head size. Other symptoms may include vomiting, sleepiness, seizures, and downward pointing of the eyes.

<span class="mw-page-title-main">Ventricular system</span> Set of structures containing cerebrospinal fluid in the brain

In neuroanatomy, the ventricular system is a set of four interconnected cavities known as cerebral ventricles in the brain. Within each ventricle is a region of choroid plexus which produces the circulating cerebrospinal fluid (CSF). The ventricular system is continuous with the central canal of the spinal cord from the fourth ventricle, allowing for the flow of CSF to circulate.

<span class="mw-page-title-main">Cerebral aqueduct</span> Conduit for CSF to the brain

The cerebral aqueduct is a narrow 15 mm conduit for cerebrospinal fluid (CSF) that connects the third ventricle to the fourth ventricle of the ventricular system of the brain. It is located in the midbrain dorsal to the pons and ventral to the cerebellum. The cerebral aqueduct is surrounded by an enclosing area of gray matter called the periaqueductal gray, or central gray. It was first named after Franciscus Sylvius.

Normal-pressure hydrocephalus (NPH), also called malresorptive hydrocephalus, is a form of communicating hydrocephalus in which excess cerebrospinal fluid (CSF) occurs in the ventricles, and with normal or slightly elevated cerebrospinal fluid pressure. As the fluid builds up, it causes the ventricles to enlarge and the pressure inside the head to increase, compressing surrounding brain tissue and leading to neurological complications. The disease presents in a classic triad of symptoms, which are memory impairment, urinary frequency, and balance problems/gait deviations. The disease was first described by Salomón Hakim and Adams in 1965.

<span class="mw-page-title-main">Interventricular foramina (neuroanatomy)</span> It is part of diencephalon that makes connection between lateral and third ventricular

In the brain, the interventricular foramina are channels that connect the paired lateral ventricles with the third ventricle at the midline of the brain. As channels, they allow cerebrospinal fluid (CSF) produced in the lateral ventricles to reach the third ventricle and then the rest of the brain's ventricular system. The walls of the interventricular foramina also contain choroid plexus, a specialized CSF-producing structure, that is continuous with that of the lateral and third ventricles above and below it.

<span class="mw-page-title-main">Dandy–Walker malformation</span> Congenital malformation of the cerebellar vermis

Dandy–Walker malformation (DWM), also known as Dandy–Walker syndrome (DWS), is a rare congenital brain malformation in which the part joining the two hemispheres of the cerebellum does not fully form, and the fourth ventricle and space behind the cerebellum are enlarged with cerebrospinal fluid. Most of those affected develop hydrocephalus within the first year of life, which can present as increasing head size, vomiting, excessive sleepiness, irritability, downward deviation of the eyes and seizures. Other, less common symptoms are generally associated with comorbid genetic conditions and can include congenital heart defects, eye abnormalities, intellectual disability, congenital tumours, other brain defects such as agenesis of the corpus callosum, skeletal abnormalities, an occipital encephalocele or underdeveloped genitalia or kidneys. It is sometimes discovered in adolescents or adults due to mental health problems.

<span class="mw-page-title-main">Colloid cyst</span> Medical condition

A colloid cyst is a non-malignant tumor in the brain. It consists of a gelatinous material contained within a membrane of epithelial tissue. It is almost always found just posterior to the foramen of Monro in the anterior aspect of the third ventricle, originating from the roof of the ventricle. Because of its location, it can cause obstructive hydrocephalus and increased intracranial pressure. Colloid cysts represent 0.5–1.0% of intracranial tumors.

<span class="mw-page-title-main">Cerebral shunt</span> Surgical implant to treat hydrocephalus

A cerebral shunt is a device permanently implanted inside the head and body to drain excess fluid away from the brain. They are commonly used to treat hydrocephalus, the swelling of the brain due to excess buildup of cerebrospinal fluid (CSF). If left unchecked, the excess CSF can lead to an increase in intracranial pressure (ICP), which can cause intracranial hematoma, cerebral edema, crushed brain tissue or herniation. The drainage provided by a shunt can alleviate or prevent these problems in patients with hydrocephalus or related diseases.

<span class="mw-page-title-main">Lutembacher's syndrome</span> Medical condition

Lutembacher's syndrome is a very rare form of congenital heart disease that affects one of the chambers of the heart as well as a valve. It is commonly known as both congenital atrial septal defect (ASD) and acquired mitral stenosis (MS). Congenital atrial septal defect refers to a hole being in the septum or wall that separates the two atria; this condition is usually seen in fetuses and infants. Mitral stenosis refers to mitral valve leaflets sticking to each other making the opening for blood to pass from the atrium to the ventricles very small. With the valve being so small, blood has difficulty passing from the left atrium into the left ventricle. Septal defects that may occur with Lutembacher's syndrome include: Ostium primum atrial septal defect or ostium secundum which is more prevalent.

Endoscopic third ventriculostomy (ETV) is a surgical procedure for treatment of hydrocephalus in which an opening is created in the floor of the third ventricle using an endoscope placed within the ventricular system through a burr hole. This allows the cerebrospinal fluid to flow directly to the basal cisterns, bypassing the obstruction. Specifically, the opening is created in the translucent tuber cinereum on the third ventricular floor.

<span class="mw-page-title-main">Choroid plexus carcinoma</span> Medical condition

A choroid plexus carcinoma is a type of choroid plexus tumor that affects the choroid plexus of the brain. It is considered the worst of the three grades of chord plexus tumors, having a much poorer prognosis than choroid atypical plexus papilloma and choroid plexus papilloma. The disease creates lesions in the brain and increases cerebrospinal fluid volume, resulting in hydrocephalus.

<span class="mw-page-title-main">External ventricular drain</span> Medical device

An external ventricular drain (EVD), also known as a ventriculostomy or extraventricular drain, is a device used in neurosurgery to treat hydrocephalus and relieve elevated intracranial pressure when the normal flow of cerebrospinal fluid (CSF) inside the brain is obstructed. An EVD is a flexible plastic catheter placed by a neurosurgeon or neurointensivist and managed by intensive care unit (ICU) physicians and nurses. The purpose of external ventricular drainage is to divert fluid from the ventricles of the brain and allow for monitoring of intracranial pressure. An EVD must be placed in a center with full neurosurgical capabilities, because immediate neurosurgical intervention can be needed if a complication of EVD placement, such as bleeding, is encountered.

<span class="mw-page-title-main">Central nervous system cyst</span> Medical condition

A central nervous system cyst is a type of cyst that presents and affects part of the central nervous system (CNS). They are usually benign and filled with either cerebrospinal fluid, blood, or tumor cells. CNS cysts are classified into two categories: cysts that originate from non-central nervous system tissue, migrate to, and form on a portion of the CNS, and cysts that originate within central nervous system tissue itself. Within these two categories, there are many types of CNS cysts that have been identified from previous studies.

Bobble-head doll syndrome is a rare neurological movement disorder in which patients, usually children around age 3, begin to bob their head and shoulders forward and back, or sometimes side-to-side, involuntarily, in a manner reminiscent of a bobblehead doll. The syndrome is related to cystic lesions and swelling of the third ventricle in the brain.

<span class="mw-page-title-main">Subependymal giant cell astrocytoma</span> Medical condition

Subependymal giant cell astrocytoma is a low-grade astrocytic brain tumor (astrocytoma) that arises within the ventricles of the brain. It is most commonly associated with tuberous sclerosis complex (TSC). Although it is a low-grade tumor, its location can potentially obstruct the ventricles and lead to hydrocephalus.

<span class="mw-page-title-main">ShuntCheck</span> Diagnostic medical device

ShuntCheck is a non-invasive diagnostic medical device which detects flow in the cerebral shunts of hydrocephalus patients. Neurosurgeons can use ShuntCheck flow results along with other diagnostic tests to assess shunt function and malfunction.

Cerebrospinal fluid (CSF) flow MRI is used to assess pulsatile CSF flow both qualitatively and quantitatively. Time-resolved 2D phase-contrast MRI with velocity encoding is the most common method for CSF analysis. CSF Fluid Flow MRI detects back and forth flow of Cerebrospinal fluid that corresponds to vascular pulsations from mostly the cardiac cycle of the choroid plexus. Bulk transport of CSF, characterized by CSF circulation through the Central Nervous System, is not used because it is too slow to assess clinically. CSF would have to pass through the brain's lymphatic system and be absorbed by arachnoid granulations.

References

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  2. 1 2 3 4 5 "Aqueductal Stenosis". Nervous System Diseases. Retrieved 15 October 2013.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Cinalli, G.; Spennato, P.; Nastro, A.; Aliberti, F.; Trischitta, V.; Ruggiero, C.; Mirone, G.; Cianciulli, E. (Oct 2011). "Hydrocephalus in aqueductal stenosis". Childs Nervous System. 27 (10): 1621–42. doi:10.1007/s00381-011-1546-2. PMID   21928028.
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  5. 1 2 Seiler, F. Arran; Sean M. Lew (2010). "Aqueductal Stenosis Presenting as Isolated Tremor: Case Report and Review of the Literature". Pediatric Neurosurgery. 46 (5): 392–5. doi:10.1159/000323419. PMID   21412026.
  6. ↑ Mucchiut, M.; L. Valentinis; F.Tuniz; B. Zanotti; M. Skrap; P. Bergonzi; G. Zanchin (Oct 2007). "Adult aqueductal stenosis presenting as a thunderclap headache: a case report". Cephalalgia. 27 (10): 1171–1173. doi:10.1111/j.1468-2982.2007.01379.x. PMID   17655718.
  7. ↑ Levitsky, D. B.; L. A. Mack; D. A. Nyberg; D. B. Shurtleff; L. A. Shields; H. V. Nghiem; D. R. Cyr (March 1995). "Fetal aqueductal stenosis diagnosed sonographically: how grave is the prognosis?". AJR Am J Roentgenol. 164 (3): 725–30. doi: 10.2214/ajr.164.3.7863902 . PMID   7863902.
  8. 1 2 McMillan, J. J.; Williams, B. (June 1977). "Aqueduct stenosis. Case review and discussion". Journal of Neurology, Neurosurgery, and Psychiatry. 40 (6): 521–532. doi:10.1136/jnnp.40.6.521. PMC   492757 . PMID   302852.
  9. 1 2 Bergsneider, Marvin; Miller, C.; Vespa, P. M.; Hu, X. (February 2008). "Surgical management of adult hydrocephalus". Neurosurgery. 62: 643–59, discussion 659–60. doi:10.1227/01.neu.0000316269.82467.f7. PMID   18596440.
  10. 1 2 Guillaume, D. J. (Oct 2010). "Minimally Invasive Neurosurgery for Cerebrospinal Fluid Disorders". Neurosurgery Clinics of North America. 21 (4): 653–72, vii. doi:10.1016/j.nec.2010.07.005. PMID   20947034.
  11. 1 2 Villani, Roberto; Giustiro Tomei; Sergio M Gaini; Nadia Grimoldi; Diego Spagnoli; Lorenzo Bello (Mar 1995). "Long-term outcome in aqueductal stenosis". Child's Nervous System. 11 (3): 180–5. doi:10.1007/BF00570262. PMID   7773981.
  12. 1 2 "Hydrocephalus Fact Sheet". National Institute of Neurological Disorders and Stroke. National Institutes of Health. Archived from the original on 27 July 2016. Retrieved 16 October 2013.
  13. ↑ Peretta, P; G. Cinalli; P. Spennato; P. Ragazzi; C. Ruggiero; F. Aliberti; C. Carlino; E. Cianciulli (Sep 2009). "Long-Term Results Of A Second Endoscopic Third Ventriculostomy In Children: Retrospective Analysis Of 40 Cases". Neurosurgery. 65 (3): 539–47, discussion 547. doi:10.1227/01.NEU.0000350228.08523.D1. PMID   19687699.
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