Keywords
dorsum sellae - endoscopic third ventriculostomy - ETV - hydrocephalus - prepontine
interval - tectal glioma
Introduction
Tectal gliomas (TGs) are rare pediatric brain tumors that originate from the tectal
plate with most of these tumors being low-grade astrocytomas.[1]
[2]
[3] TG commonly presents with hydrocephalus due to obstruction of the aqueduct of Sylvius,
and this typically occurs over a long duration of time due to the slowly growing nature
of low-grade glioma.[1]
[2]
[4] In a systematic review including 355 patients with TG, 89.3% required at least one
cerebrospinal fluid (CSF) diversion procedure during their lifetime.[1] Children with TG who are ≥ 10 years and without a history of shunt insertion have
a 90% success rate of their endoscopic third ventriculostomy (ETV),[5] this makes ETV superior to ventriculoperitoneal shunt (VPS) insertion and the first
choice in children with TG who develop hydrocephalus.[3]
[6]
[7] Some anatomical variations in the floor of the third ventricle could make performing
ETV challenging in some patients and this includes diminished prepontine interval
(PPI),[8]
[9]
[10]
[11] despite this puts a risk of inadvertent injury to the basilar artery, this is not
a contraindication for the procedure and there was no arterial injury mentioned in
studies at which ETV was done with narrow PPI.[8]
[9]
[10]
We herein present a case of a child with TG who underwent ETV with an extremely diminished
PPI found intraoperatively, 1-year follow-up magnetic resonance imaging (MRI) brain
showed complete resolution of the hydrocephalus and stationary course for the TG.
Case Report
A 12-year-old male patient presented with intermittent headache and dizziness for
1 year, which became progressive 3 weeks before admission; he sought medical advice
for whom an MRI brain with contrast was done and showed massive triventricular hydrocephalus,
a diminished PPI < 1 mm, and nonenhancing tectal mass of 17 × 18 mm, mostly low-grade
glioma ([Figs. 1] and [2A]). The extraocular muscles were not affected, and fundus examination revealed grade
III papilledema. He underwent ETV ([Video 1]), intraoperatively, and we found a narrow anterior third ventricle floor with extremely
diminished PPI ([Fig. 3]). The floor was thin through which the basilar artery was visualized clearly. Using
the LOTTA rigid endoscope STORZ (GmbH & Co. Tuttlingen, Germany), we made a small
stoma using the Decq forceps through a narrow window immediately behind the dorsum
sellae (DS). The child was discharged in good condition, the headache was completely
relieved 1 week later, and 2.5 months later the fundus examination was normal. Seven
months later, an MRI brain with contrast showed dramatic improvement of hydrocephalus,
evident flow through the stoma, and stationary course of the tectal mass, which was
confirmed in a 1-year follow-up after surgery ([Figs. 2B] and [4]); the patient is still under conservative serial follow-up imaging.
Fig. 1 Preoperative magnetic resonance imaging (MRI) brain axial T2 cuts. Triventricular
hydrocephalus with obstructed flow at the 4th ventricle, tectal mass closing the aqueduct
of Sylvius (green arrows), extremely diminished prepontine interval between the basilar
artery and the clivus (red arrows), massive dilatation of the 3rd ventricle splitting
the interpeduncular cistern, permeation through the ventricular wall (orange arrows),
and absence of differentiation of cortical sulci and gyri.
Fig. 2 (A) Preoperative magnetic resonance imaging (MRI) brain sagittal T1 cut, compressed
midbrain from massive chronic hydrocephalus (blue arrow), tectal mass closing the
aqueduct of Sylvius (green arrow). (B) Postoperative MRI brain sagittal T2 cut after a 1-year follow-up, resolved hydrocephalus
with normal appearance of the midbrain (blue arrow), tectal mass closing the aqueduct
of Sylvius (green arrow), evidence of signal voids of cerebrospinal fluid (CSF) flow
across the stoma on the floor of the 3rd ventricle up to the lateral ventricle (yellow
arrows), the extremely diminished prepontine interval between the basilar artery and
the clivus (red arrow) still evident in the postoperative MRI.
Fig. 3 Intraoperative endoscopic views during performing the endoscopic third ventriculostomy
(ETV). (A) The 3rd ventricle floor before performing the ETV, the extremely diminished prepontine
interval between the basilar artery (orange arrows) and dorsum sellae (purple arrows),
black asterisks point to the mammillary bodies. (B) Using the Decq forceps and creating the stoma just behind the dorsum sellae. (C) Widening of the stoma with Decq forceps while doing mild elevation of the thinned
floor to be safe and away from the basilar complex. (D) Endoscopic view showing patent stoma under irrigation. (E) Visual inspection through the edges of the stoma for confirmation of the naked basilar
artery in the subarachnoid space (orange arrows). (F) A view from the posterior 3rd ventricle floor shows obstruction of the aqueduct
of Sylvius with no bulge inside the 3rd ventricle (black arrows).
Fig. 4 Postoperative magnetic resonance imaging (MRI) brain axial T2 cuts after a 1-year
follow-up. A decrease in the ventricular size after endoscopic third ventriculostomy
(ETV), tectal mass closing the aqueduct of Sylvius (green arrows), still evident extremely
diminished prepontine interval (red arrow), resolution of the preoperative permeation
through the lateral ventricle wall, and restoration of normal cerebrospinal fluid
(CSF) at the cortical level with differentiation between sulci and gyri.
Video 1
Discussion
A diminished PPI has been defined as the distance between the upper portion of the
basilar artery and the DS of ≤ 1 mm.[8]
[9]
[10] This anatomical variant is not a contraindication to perform an ETV, studies which
reported ETV with diminished PPI did not mention vascular injuries in those patients,[8]
[9]
[10] the use of stereotactic guidance, intraoperative Doppler, and making a blunt fenestration
at the DS after palpation of the bone or immediately behind the DS are important tips
to decrease vascular injury.[8]
[9]
[10]
[11] The presence of a thinned floor with clear visualization of the basilar and posterior
cerebral arteries should encourage the neurosurgeon to make a blunt penetration under
vision on the DS or immediately behind it in front of the basilar artery,[8] and even a small stoma would be enough after visual confirmation of the basilar
artery through the stoma.
Obstructive hydrocephalus is a typical presentation of TG due to the interruption
of CSF flow across the aqueduct of Sylvius.[1]
[2]
[3]
[4] Management of TG consists of radiological surveillance with close clinical and radiological
follow-up owing to their indolent course, and CSF diversion for the associated hydrocephalus
either through ETV or placement of VPS.[1]
[2]
[6] According to the ETV success score, children with TG older than 10 years without
a history of VPS insertion have a 90% success rate of the ETV.[5] ETV has been reported with high success rates managing the hydrocephalus-associated
TG with 82,[4] 85,[12] 89,[13] and 100%[3] of patients being shunt free at the last follow-up.
A multicenter study including 761 children showed that the original ETV success score
still has a good predictive ability to predict the success of ETV, and diminished
PPI was not mentioned as a risk factor for ETV failure.[14] Children with the highest chance of ETV success[5]
[14] should take their chance completely because this means avoiding lifelong shunt dependency,
shunt infection, and the possibility of overdrainage.[1]
[7]
[12] Unless intraoperative safety is not guaranteed, diminished PPI is not a contraindication
for doing ETV, especially in patients with thinned floors with clearly visualized
underlying vascular structures.
Conclusion
Diminished PPI is not a contraindication for doing ETV unless safety cannot be guaranteed,
and it was not proven to be a risk factor for ETV failure. Creating a stoma on the
DS after palpating the bone or just behind it using blunt fenestration is a safe way
especially in the presence of a thinned third ventricle floor with clearly visualized
vascular structures.
