Keywords
aqueductal - stenosis - congenital - high-riding basilar - subdural - hematoma
Introduction
Congenital aqueductal stenosis (CAS) is the most common form of noncommunicating hydrocephalus.
A complete or partial obstruction of cerebrospinal fluid (CSF) happens at the aqueduct
of Sylvia's during fetal life, which results in the dilation of the lateral and third
ventricles with normal-sized fourth ventricle. Three quarters of CAS patients had
unknown etiology, though there were many etiologies of this disorder including infection,
hemorrhage, intoxication, deficiencies, genetic factors, central nervous system malformation,
and tumors.[1] Some patients with CAS might not show any symptoms until adulthood, or there might
be mild symptoms that might pass unnoticed or undocumented. Usually in a small percentage
of acute onset in adults, symptoms may be present for 1 to 4 weeks. Symptoms would
include headache, nausea, vomiting, visual disturbances, seizures, changes in mental
state, and coma. More often the onset is subacute where the symptoms from less than
6 months or chronic for more than 5 months, the symptoms would be characterized by
intracranial hypertension syndrome progressively taking hold.[2] Given the diverse etiologies and variable presentation of CAS ranging from asymptomatic
cases in early life to acute or subacute symptom onset in adulthood, the management
and long-term follow-up of such cases present significant clinical challenges. Against
this backdrop of complexity, this study describes a case of adult-onset CAS treated
with shunt surgery, with an 11-month follow-up.
Case Presentation
In 2023, a 35-year-old man known case of allergic sinusitis presented to the emergency
department complaining of severe headache for 2 days and vomiting several times for
1 day. Clinical examination revealed a normal neurological examination. Computed tomography
(CT) of the brain without contrast showed lateral and third ventriculomegaly associated
with enlargement of the proximal aqueduct of Sylvius and normal-sized fourth ventricle.
While the endoscopic third ventriculostomy (ETV) procedure was initially considered
due to its high rate of success, the decision was ultimately made to insert an emergency
external ventricular drain (EVD) instead. This was due to the patient presentation
with a high-riding basilar artery, as showed in [Fig. 1], which increased the risk of vascular injury from the ETV—a risk that carries potentially
fatal consequences. The patient improved clinically afterward. CSF analysis was unremarkable.
Postoperative magnetic resonance imaging (MRI) three-dimensional (3D) fast imaging
employing steady-state acquisition of the brain showed marginal reduction in the lateral
and third ventriculomegaly and a thin tissue membrane separating the dilated aqueduct
from the normal-sized fourth ventricle, in keeping with the aqueductal web ([Fig. 1]).
Fig. 1 Postoperative MRI 3D FIESTA of the brain indicates aqueductal stenosis. Sagittal
3D FIESTA sequence of the brain shows marginal reduction in the lateral and third
ventriculomegaly accompanied by the normal-sized fourth ventricle. There is a thin
tissue membrane (green arrowhead) separating the dilated aqueduct from the normal-sized
fourth ventricle, in keeping with the aqueductal web. FIESTA, fast imaging employing
steady-state acquisition; MRI, magnetic resonance imaging; 3D, three-dimensional.
Afterward, EVD was removed and a ventriculoperitoneal shunt medium pressure valve
was inserted. On follow-up, after 13 days, the patient complained of blurring of vision.
Accordingly, optical coherence tomography (OCT) was done, which showed mild bilateral
papilledema.
After 3 months postoperatively, he was readmitted with a history of multiple motor
vehicle accidents, complaining of difficulty concentrating and dysgraphia. His clinical
examination was intact except for an equivocal Babinski sign. He underwent an urgent
CT scan of the brain that showed a large left subdural isodense hematoma. He underwent
emergent frontoparietal craniotomy with hematoma evacuation and opening of septations.
Postoperative CT of the brain showed significant radiological regression.
After 2 months of follow-up, an MRI of the brain revealed a recollection of left side
hypointense chronic subdural hematoma (CSDH) ([Fig. 2]). Accordingly, the medium pressure valve has been replaced with a programmable valve,
which the patient has become stable and clinically improved after.
Fig. 2 MRI of the brain reveals a left recollection of subdural hematoma. Axial T2-MRI of
the brain showed a left holohemispheric subdural hypointense hematoma measuring about
1.9 cm in maximum depth with midline shift measuring about 0.3 cm. MRI, magnetic resonance
imaging.
Discussion
CAS is inherited primarily in an X-linked fashion and shows male predominance.[3] CAS is 0.5 to 1 per 1,000 births in the pediatric group.[4] CAS became a well-documented condition within the young population. However, late
presentation is a rare phenomenon where the incidence of CAS in adults has not been
documented yet, despite this there are few case reports and case series regarding
late CAS.[4]
[5]
Patients with aqueductal stenosis (AS) present with headaches, seizures, vomiting,
visual problems, postural disturbances, incontinence, impairment in wakefulness, cognitive
function, and endocrine dysfunction.[6]
[7]
[8]
[9] Uncommon symptoms include CSF rhinorrhea, trigeminal neuralgia, hearing loss, and
vertigo.[7]
[8]
[10] Older children, adolescents, and adults could present in acute (symptoms for 1–4
weeks), subacute (symptoms for less than 6 weeks), or chronic (symptoms for more than
6 weeks) manner.[1]While the clinical picture is similar, the literature shows variability according
to age. Due to the elevation of intracranial pressure, headaches are the most encountered
sign and the most notable in the young population.[1]
[10] The older populations' symptoms tend to mimic those of normal pressure hydrocephalus,
such as urinary and fecal incontinence and impairment in gait, posture, memory, and
wakefulness.[2]
[8]
[9]
[11]
[12] However, one study stated the occurrence of these symptoms in most patients regardless
of age but are milder in the younger population and are overshadowed by headaches
and other signs of increase intracranial pressure.[9] The significance of symptom duration and severity regarding the prognosis was noted
in one study in which abrupt and severe onset of symptoms resulted in poorer outcomes.[5] In contrast, another study indicated the irrelevance of symptom duration regarding
age or severity.[9]
Few hypotheses were proposed regarding the relative asymptomatic childhood and symptomatic
adulthood. One hypothesis suggests that the decompensation of a prior compensated
hydrocephalus causes the late onset of symptoms.[8] Another hypothesis explains a two-hit process in which the increased resistance
of CSF flow due to deep white matter ischemia can participate in manifesting the symptoms
during adulthood.[12]
[13] The subject of our case presented signs of increased intracranial pressure consisting
of a severe headache spanning over the course of 2 days and several vomiting episodes
with no impairment in visuals, gait, balance, wakefulness, defecation, or voiding.
Rodis et al recently proposed a classification of AS into four clinical subtypes,
I to IV (based on patient age). In our case, the patient met type III AS (acute type),
which is more frequent in adolescence and early adulthood. Also, headaches and signs
of raised intracranial pressure were predominant symptoms of this type.[1]
Generally, advanced MRI techniques are needed in order to diagnose and determine the
etiology of the stenosis. Phase-contrast MRI aids in evaluating aqueductal patency.[14] Recent studies have shown that 3D (sampling perfection with application optimized
contrast using different flip angle evolutions) with the variant flip angle mode technique
is beneficial in demonstrating luminal morphology and alone is usually sufficient
for the diagnosis of AS.[15]
[16] The typical morphology of AS includes funneling of the aqueduct above the site of
stenosis, lateral and third ventriculomegaly, and an upward bowing of the corpus callosum.[1]
[17] In our case, CT of the head revealed enlargement of the lateral and third ventricles,
a proximal dilation of the aqueduct of Sylvius preceding the stenosis, and a normal-sized
fourth ventricle.
Currently, three surgical treatment options are available: ETV, shunt surgery, and
endoscopic aqueductoplasty. ETV operation, which re-establishes the physiological
CSF route, is characterized by fewer complications, and the need for a revision is
low, making ETV the preferred treatment option. Shunt surgery is highly effective;
it can be used as a first-line or second-line treatment option in the cases of recurrence
after ETV or if ill-suited anatomical conditions are present, for instance in [Fig. 1], a high-riding basilar artery is located anterior to the pons and closely adjacent
to the floor of the third ventricle (tuber cinereum), making ETV unfavorable. However,
in shunt surgery, there is a high complication rate, and revisions are common.[17] Endoscopic aqueductoplasty is considered to be a substitute for ETV in a very selected
patient group, such as those with short AS and membranous occlusion. The reobstruction
and complication rate are high, given the critical nature of the mesencephalon; structures
such as the tegmentum and the tectum can be affected, resulting in oculomotor, trochlear
nerve palsies, and Perinaud's syndrome.[1] In this case, an anatomical variation was present, the patient had a narrow prepontine
cistern and a high-riding basilar artery. This played a role in the treatment option
of CAS where in most individuals, the basilar artery bifurcates into the two posterior
cerebral arteries at the upper border of pons. In the case of a high-riding basilar
artery, the aforementioned bifurcation happens directly under the floor of the third
ventricle, making the ETV operation which fenestrated the floor of the third ventricle
a high-risk operation. Therefore, shunt surgery was preferred in our case. Other surgical
approaches mentioned in the literature concerning the presence of a high-riding basilar
artery or an option in the case of the presence of a high-riding basilar artery include
ETV using a Penumbra Artemis Neuro Evacuation Device and extra-axial ETV.[18]
[19]
A follow-up took place 13 days postoperative. The report subject complained of having
blurred vision; therefore, an OCT was performed, showing mild bilateral papilledema.
As hydrocephalus progresses, a set of complications arise. Neuro-ophthalmic complications
include papilledema resulting in decreased central visual acuity due to the enlargement
of the concentric physiological blind spot in the acute presentation; however, in
the chronic presentation, preservation of central vision is seen until the late stages
due to the ischemic process affecting the arcuate nerve fiber bundle first before
the papillomacular bundle that surrounds the macula which is responsible for the high-resolution
and colored central vision. Transient visual obscuration can also be seen; it can
be triggered by movement, the patient might experience sudden blurring of the vision
or a complete grayout, but the restoration of vision is always swift and complete.[20]
Subdural hematomas can be another complication arising from shunt surgery in the case
of overdraining. The pathogenesis includes the rise in negative pressure caused by
overshunting, resulting in bridging veins becoming vulnerable due to the increased
strain caused by the separation of the brain from the dura. Osmotic mechanisms also
participate, facilitating the growth of the subdural collection.[21] In our case, after approximately 2 and a half months of placing the V/P shunt, the
patient was complicated by CSDH due to overshunting.
This case underscores the importance of individualized treatment approaches, especially
in patients with unique anatomical variations such as a high-riding basilar artery.
However, the reliance on findings from a single case poses limitations, particularly
regarding the generalizability and applicability of the treatment strategies to a
broader patient population. Consequently, there is a critical need for further research,
including larger cohort studies or controlled trials, to validate these findings and
treatment recommendations. Such studies would contribute to establishing more definitive
surgical options for CAS, ensuring safer and more effective management strategies
for these patients, especially those presenting with or at risk of complex complications.
