Surgical considerations in congenital nontumorous obstructive hydrocephalus

Suthar and Dua[1] describe a 46-year-old right-handed woman who presented with subacute headaches and normal clinical neurology suspected to be tension-type headaches. MRI showed significant enlargement of the left lateral ventricle with disproportionate involvement of the posterior body and trigone and occipital horn.[1] There was herniation of the dilated ventricular body and trigone into the posterior fossa, consistent with a ventricular diverticulum. The differential diagnosis on MRI was an intraventricular arachnoid cyst with a rare intraventricular membrane or an epidermoid cyst. Ventriculoscopic fenestration of the intraventricular membrane in the left lateral ventricle was performed. On follow-up MRI at 3 months, there was a decrease in the size of the left lateral ventricle and ventricular diverticulum, with improvement in the posterior fossa mass effect as well as resolution of tonsillar herniation.

Progressive ventricular dilatation can result in diverticuli and periventricular white matter loss. Intraventricular diverticulum are extensions or focal outpouching of the ventricle lined by a prolapsed ependymal layer.[2,3] It occurs in the setting of longstanding hydrocephalus and resolves following treatment for hydrocephalus. The common causes include post neuroendoscopy, shunt placements, hemorrhage, and clinically silent focal ischemia. It may also occur due to acute intracranial hypertension caused by a large subacute subdural hematoma. However, sometimes, they are seen in areas that are not within a well-defined vascular territory or secondary to a neurosurgical intervention or previous focal hemorrhage. They are also seen without an identifiable focal surgical, vascular, or traumatic etiology. The focal diverticulum can expand into surrounding corridors or fissures, exerting a pressure effect. A supracerebellar extension route of the ventricular diverticulum suggests that the medial choroidal fissure in the antrum and the velum interpositum may be important anatomical structures for the extension of the lateral ventricular diverticulum into the supracerebellar cistern. The expansion of the pia and arachnoid membranes toward the supracerebellar region is believed to originate through the tela choroidea of the temporal choroid plexus or of the antral choroid plexus.[2,3] The diverticuli in the anterior ventricular segment are usually the result of obstructive lesions in the anterior portion of the lateral ventricle, the foramen of Monro, and the anterior portion of the third ventricle. They may also occur along the suprapineal and infrapineal recesses of the third ventricle and the superior portion of the fourth ventricle.[4,5] A recent study suggested that the presence of ventricular diverticula at the level of the temporal horn might also be explained by the less compact packing of the subependymal white matter bundles in this region.[3] The diffuse tensor imaging (DTI) study of a patient who presented with hemiparesis consistent with the intraparenchymal lesion revealed that the corticospinal tract was partly included in the septum between the ventricle and the intraparenchymal diverticulum.[3] Radiologic diagnosis is challenging and requires close attention.[4]

They should be distinguished from other cystic lesions in the quadrigeminal region, viz. infratentorial arachnoid cyst. The detection of an ostium of a diverticulum or communication between the cyst and the ventricular system is paramount for diagnosis. The association of ventricular diverticula with intra- and paraventricular tumors causing obstructive hydrocephalus has rarely been reported.

The presence of an intraventricular membrane within the ventricular diverticulum is a rare phenomenon. Diagnosis is difficult, and high-resolution MR imaging with close observation is necessary. An intraventricular arachnoid cyst can be a close mimic, but authors have noticed that the choroid plexus in the center of the dilated ventricle excludes an arachnoid cyst.

There is also a need for awareness regarding pseudodiverticuli of dilated ventricles, which are focal periventricular CSF collections along the temporal-occipital horns.[5] The increased ventricular pressure causes progressive shearing and weakening of the ependyma and consequent herniation into the brain parenchyma through a small defect within the ependymal wall into the subarachnoid spaces. The fluid collections follow the principal course of the white matter tracts within the occipital and temporal lobes and communicate with the adjacent lateral ventricles through an ependymal defect. The CSF follows the main course of the fibers within the temporal lobes and appears to displace or dissect the fibers along the periphery of the fluid collection. Ventricular pseudodiverticula must be differentiated from classic porencephalic cysts secondary to periventricular ischemia or hemorrhage. In porencephalic cysts, periventricular white matter tracts are damaged or interrupted. DTI can be used to differentiate between a porencephalic cyst with interrupted fibers and a pseudodiverticulum or true ventricular diverticulum in which the fibers are intact but displaced or splayed apart by the focally accumulating CSF leaked from the ventricles.[5]

To conclude, clinicians dealing with chronic severe obstructive hydrocephalus should be aware of ventricular intraparenchymal diverticulation.