Keywords
third ventricle - transcallosal interhemispheric - subependymoma
Introduction
Subependymomas are rare noninvasive benign lesions of ependymal origin and were first
described by Scheinker and Scheinker 1945.[1] Previous studies reported that of all World Health Organization (WHO) grade I subependymomas,
50 to 60% occur in the fourth ventricle and 30 to 40% occur in the lateral ventricles,
but those in the third ventricle are rare.[2]
[3]
[4]
[5] In addition, grade I subependymomas are extremely rare in adults, whereas ependymomas
in the fourth ventricle are more common in children.[6] In the literature, serious complications have been reported in the early postoperative
period because of the characteristics of the tumor or continuous use of brain retractors
for the transcallosal interhemispheric approach used to reach the lateral ventricle.[7]
In the present study, we discuss the advantages of the lateral horizontal head position
and transcallosal interhemispheric approach using two cotton pads in a case of acute
hydrocephalus anterior third ventricle subependymoma with clinical and surgical findings
consistent with those reported in the relevant literature.
Case Report
On March 15, 2021, a 40-year-old male patient was brought to the emergency department
of our hospital. Physical examination revealed stable vital signs, but the patient
was highly confused, had meaningless speech, and convulsions, with a Glasgow Coma
Scale (GCS) score of 7. Noncontrast-enhanced brain computed tomography in the emergency
department revealed unilateral asymmetric acute hydrocephalus and a suspicious lesion
at the level of the foramen of Monro in the left lateral ventricle ([Fig. 1]). Emergent ventriculostomy was performed. In the 18th hour of cerebrospinal fluid
(CSF) drainage, the patient's GCS score increased to 13 to 14 on neurological examination
(NE). Brain magnetic resonance imaging (MRI) revealed a contrast-enhancing lesion
extending from the third ventricle to the left lateral ventricle, with a diameter
of 22 × 28 mm, and acute hydrocephalus ([Fig. 2]). Surgery was performed on March 17, 2021, via the transcallosal interhemispheric
approach.
Fig. 1 Preoperative head computed tomography in the axial plane showing acute hydrocephalus
and a suspicious lesion at the level of the foramen of Monro in the left lateral ventricle
(red arrow).
Fig. 2 Preoperative contrast-enhanced T1-weighted axial brain magnetic resonance imaging
scan showing a mild, contrast-enhancing, well-demarcated solid lesion extending from
the third ventricle to the left lateral ventricle, with a diameter of 22 × 28 mm,
and unilateral acute hydrocephalus (red arrow).
Surgical Position and Technique
Surgical Position and Technique
The patient was anesthetized and placed in the supine position. Then, the patient
was turned to the left lateral decubitus position at a ratio of 2:3 from the supine
position. Next, the head was lifted 45 degrees, turned 20 to 30 degrees to the left,
and the neck was brought to 0 to 5 degrees flexion. The patient was then fixed with
a skull-pin head holder ([Fig. 3]). Free craniotomy was performed in the left frontoparietal region, with two-thirds
of the 3 × 3 cm free craniotomy flap on the left side encompassing the superior sagittal
sinus (SSS). The dura mater base was opened in a C shape with the same length of the
SSS. Upon entering the interhemispheric corridor with the falx, two 2 × 2 cm round
cotton pads, which would replace intermittent brain retractors, were placed in front
of and behind the craniotomy flap. With the help of the two cotton pads placed in
the surgical area, the corpus callosum was reached easily by dissecting the cingulate
gyrus at the free edge of the falx. A 1.5 cm callosotomy was performed in the foramen
of Monro by using an intraoperative neuronavigation control. After the left lateral
ventricle was opened, the following tumor surgery procedures were continued with the
surgical view provided by the cotton pads that were placed on the field ([Fig. 4]). Thereby, we minimized any additional trauma caused by continuous use of brain
retractors. The lesion in the left lateral ventricle was clear and dirt-white in color
and was at the level of the foramen of Monro, extending into the third ventricle with
prominent capillaries and a cream-white-colored surface ([Fig. 5]). After confirming that it was solitary and pedunculated, the small connection was
cut, and en bloc resection was performed ([Fig. 6]) After the lesion was removed, the CSF passage was found to be provided by the third
ventricle, and the ventriculostomy catheter was removed. Histopathological examination
revealed that the lesion was a WHO grade I subependymoma ([Fig. 7A, B]). The patient's control postoperative contrast-enhanced brain MRI scan showed that
the left lateral ventricle was asymmetrically larger than the right lateral ventricle
([Fig. 8]). The patient did not have neurological deficits in the early postoperative period
and was discharged on the 10th postoperative day. No neurological deficits were observed
in the NE performed in the third and sixth month.
Fig. 3 Surgical position: The head is raised 45 degrees, turned 20 to 30 degrees to the
left, and the neck is brought to 0 to 5 degrees flexion. The patient is fixed with
a head holder.
Fig. 4 Schematic illustration of the positioning and surgical corridor provided by the interhemispheric
transcallosal approach with the help of two round cotton pads placed in the surgical
area. Abbreviations: 3V, third ventricle; Tm, tumor; Rcp, round cotton pad; PcaA,
pericallosal artery.
Fig. 5 The lesion in the left lateral ventricle is clear and dirt-white in color. It is
at the level of the foramen of Monro, extending into the third ventricle, with prominent
capillaries, and a cream-white-colored surface.
Fig. 6 Macroscopic appearance of the tumor.
Fig. 7 (A, B) Histopathologic examination result showing a subependymoma with microcysts filled
with myxoid substance and clusters of small uniform cells embedded in the fibrillary
background (hematoxylin-eosin staining, original magnifications: A ×40, and B ×100).
Fig. 8 Control of early postoperative contrast-enhanced T1-weighted brain magnetic resonance
imaging in the axial plane. The tumor is totally resected, and the right lateral ventricle
is moderately dilated.
Discussion
The WHO grade I anterior third ventricle subependymomas are usually detected during
autopsies in cases of sudden death due to acute or intermittent obstruction of the
CSF passage, sometimes when neuroimaging is performed during NE for complaints of
headache, amnesia, behavioral disorders, and sometimes as part of routine screening
tests for those admitted to the emergency services due to trauma or injury.[6]
[8] When pure third ventricle subependymomas reach approximately 2 cm in size, they
can become symptomatic by causing CSF flow blockage in the foramen of Monro.[9] Hydrocephalus has been reported in 94% of intraventricular symptomatic supependymomas.[10] Subependymomas have been mostly found in the ventricular lumen and rarely found
in the brain parenchyma.[11] In addition, subependymomas cause central herniation or sudden death due to unilateral
acute hydrocephalus with obstruction of the CSF passage from the third ventricle.[12]
[13]
In our case, the patient presented with complaints of acute hydrocephalus, with a
22 × 28 mm diameter lesion, which almost became compatible with the anatomy of the
anterior third ventricle. In a 20-year period, Fujisawa et al reported only five subependymoma
cases among 1,500 brain tumors, three of which were in the foramen of Monro, one was
in the right foramen of Monro, and the other was in the septum pellucidum.[9] Of the cases, one was diagnosed after a traffic accident; one because of semicoma;
one because of sleepiness; and one on evaluation of headaches. Patients usually die
of acute hydrocephalus before surgical treatment, and the lesions are detected in
autopsies.
The gravity effect of the surgical approach chosen during surgical planning for deeply
located lesions such as the lateral or anterior third ventricle, the chosen head position,
or the protection of the cortical veins during interhemispheric dissection is crucial
in preventing postoperative neurological deficits or complications. In addition, continuous
brain retractor application in the surgical approach chosen for these lesions is also
among the important risk factors for the emergence of possible neurological deficits.
The transcallosal interhemispheric approach was first used in 1922 by Dandy to expose
the posterior transcallosal interhemispheric corridor to further expose the third
ventricle, and this approach was developed by Stein.[14]
[15] Transcallosal interhemispheric intervention is more frequently preferred than the
transcortical approach to reach the anterior and middle parts of the third and lateral
ventricles because of the low risks of complications such as hemiparesis and epilepsy.[16] Previous studies reported that even if the transcallosal interhemispheric approach
is well tolerated as compared with the transcortical approach, serious complications
such as hemiparesis, amnesia, mutism, aphasia, cranial nerve VI and VII pareses, and
tactile transfer deficits can be observed.[7]
[17] The first study to prevent these serious fatal complications was conducted by Clark
in 1988, who described the lateral horizontal head position and gravity-assisted technique.[18] By modifying this technique, Shevach et al applied the horizontal head position
and gravity assist by lifting the head 45 degrees in 15 patients with lateral ventricle
or midline lesions.[19] The authors emphasized the importance of turning the head laterally and upward for
the gravity-assisted lateral horizontal head position in planning surgery to preserve
venous blood flow from the brain in the transcallosal interhemispheric approach. In
our preferred approach, gravity support, lateral horizontal head position, use of
two cotton pads, adequate anesthetic support, adequate brain laxity, and especially
gentle microdissection of the cingulate gyrus and additional CSF drainage after the
incision of the corpus callosum increase the surgical field of vision and eliminate
the need for the continuous use of brain retractors during intraventricular tumor
surgery. The tumor surgical procedure is continued safely and securely with the view
provided by the two cotton pads placed in front of and behind the craniotomy flap.
With the aid of the two cotton pads, the possible surgical complications of these
deeply located lesions are minimized by preventing contusions; lacerations of the
brain tissue, especially during dissection of the cingulate gyrus; or edema related
to vasospasm of the pericallosal arteries from the vascular structures. In addition,
through our approach, a wide viewing angle is provided by the two cotton pads used
inside the brain, allowing a wide microscopic area and panoramic view from the lateral
ventricle, genu anteriorly, and atrium posteriorly.
Conclusion
Subependymomas are rare benign, slow-growing, solitary, and pedunculated intraventricular
lesions. With correct diagnosis and urgent surgical treatments, as in our patient,
the prognosis is excellent. We believe that by applying the principles of our preferred
surgical approach (use of two cotton pads, gravity assist, lateral horizontal head
position, and nonuse of continuous brain retractors), an alternative method can be
created for reducing the risks of perioperative brain edema, additional postoperative
neurological deficits, and complications, which are more common in standard approaches
for third ventricle lesions.
