Intraventricular membrane with ventricular diverticulum

A 46-year-old right-handed woman presented to the neurology clinic with band-like headaches for 3 weeks. The headache was constant and 6/10 in severity; there were no aggravating or relieving factors, fever, or neck stiffness. Neurological examination was normal without motor or sensory deficits. Kernig and Brudzinski signs were negative. Clinical examination and symptomatology were indicative of tension-type headache; however, magnetic resonance imaging (MRI) of the brain was obtained to exclude other causes. Contrary to the expectation, the MRI showed significant enlargement of the left lateral ventricle with disproportionate involvement of the posterior body, trigone, and occipital horns [Figure 1a]. In addition, there was herniation of the dilated ventricular body and trigone into the posterior fossa consistent with a ventricular diverticulum [Figure 1a and b]. The diverticulum was seen causing a significant mass effect on the cerebellum with a 1.2 cm inferior descent of the tonsils [Figure 1b]. There were no mass lesions to suggest an underlying obstructive hydrocephalus. The tectal plate, the cerebral aqueduct, and right lateral ventricle were normal. Upon closer inspection of the dilated left lateral ventricle, thin curvilinear enhancement was seen at the level of the left foramen of Monroe [Figure 1c]. Based on the MRI findings, a provisional differential of an intraventricular arachnoid cyst was suggested; with a rare intraventricular membrane being the other possibility. The absence of restricted diffusion helped rule out an epidermoid cyst. The patient underwent ventriculoscopy, which revealed an intraventricular membrane in the left lateral ventricle corresponding to the curvilinear enhancement seen on MRI. The membrane was fenestrated, and an external ventricular drain was placed to decompress the left lateral ventricle. No cyst wall was seen ruling out an intraventricular arachnoid cyst. Follow-up MRI at 3 months showed a decrease in size of the left lateral ventricle and ventricular diverticulum with improved posterior fossa mass effect with resolution of tonsillar herniation [Figure 2a and b].

Figure 1.

(a) MRI brain coronal T2 weighted image; (b) unenhanced sagittal T1 weighted image, and; (c) contrast-enhanced axial T1 weighted image showing significant enlargement of the posterior left lateral ventricle [solid white arrow in (a)] with herniation of the dilated left ventricular body and trigone into the posterior fossa consistent with a ventricular diverticulum [dashed white arrow in (a) and (b)]. Diverticulum seen causing mass effect on the cerebellum with 1.2 cm inferior descent of the tonsils [open white arrow in (b)] and thin curvilinear enhancement at the level of the left foramen of Monroe [solid white arrow in (c)]. Choroid plexus seen in the center of dilated left ventricle [black arrowhead in (a)] ruling out an intraventricular arachnoid cyst

Figure 2.

(a) Follow-up contrast-enhanced axial T1 weighted MRI image, and; (b) unenhanced sagittal T1 weighted MRI image showing fenestration changes in left lateral ventricular intraventricular membrane [solid white arrow in (a)]) with decreased size of the left lateral ventricle [solid white arrowheads in (a)] and ventricular diverticulum with reduced posterior fossa mass effect [dashed white arrow in (b)] with resolution of tonsillar herniation [open white arrow in (b)]. There is reduced right ventricular dilation from entrapment [black arrow with white outline in (a)]

A ventricular diverticulum is a localized outpouching of a dilated ventricle and is usually seen in the setting of severe long-standing obstructive hydrocephalus.[1] The vast majority of such ventricular diverticuli involves the ventricular atrium and herniate in the posterior fossa, as in the present case. Clinical presentation is often related to posterior fossa mass effect in addition to signs and symptoms of hydrocephalus. Common etiologies for unilateral ventricular diverticulum include colloid cysts, choroid plexus tumors, and arachnoid cysts. However, unilateral membranous obstruction at the foramen of Monroe, as seen in the present case, has rarely ever been reported. Identification of the membrane is often difficult on routine imaging and high-resolution imaging techniques are needed, as shown. Differential for intraventricular membrane is intraventricular arachnoid cyst. Intraventricular arachnoid cysts are typically seen in the trigone of lateral ventricle.[2] Unlike arachnoid membranes, arachnoid cysts often cause localized mass effects including displacement of the choroid plexus. In retrospect, in the present case, the choroid plexus was in the center of the dilated ventricle excluding an arachnoid cyst [Figure 1a]. Endoscopic neurosurgical fenestration of membrane is the treatment of choice; the prognosis is good, and recurrence of symptoms is seldom seen.[3]

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