Fourth Ventricular Entrapment Caused by Rostrocaudal Herniation following Shunt Malfunction

Abstract

The subacute development of isolated fourth ventricle (IFV) is a recognized complication following shunting of the lateral ventricles for congenital and acquired hydrocephalus. We present an unusual case of acute IFV in a clinical setting which has not previously been described. Subsequent to rostrocaudal herniation caused by an obstructed frontally placed ventricular catheter, IFV developed in our patient 24 h following shunt revision, necessitating placement of an additional fourth ventricle shunt system. No signs of intraventricular hemorrhage or cerebrospinal fluid (CSF) infection were detected at the time of shunt revision and there was no documentation of similar events in the perinatal history. Dependent upon the actual underlying etiology of this child’s hydrocephalus, we hypothesize that two mechanisms may have accounted for this unusual and precipitous development of IFV. Following rostrocaudal herniation and caudal shift of the brainstem, progressive edema in the pons developed. If communicating hydrocephalus was the primary etiology, then midbrain edema occluded the aqueduct of Sylvius, preventing retrograde flow of CSF to the shunt. A distinctly different mechanism for acute IFV must be invoked if aqueductal stenosis was the preexisting cause for congenital hydrocephalus. Following herniation, brainstem displacement and edema resulted in obliteration of the lateral pontine and ambient cisterns, preventing the normal rostral migration of CSF around and over the mesencephalon. Cerebellar tonsillar herniation with impaction of the tonsils into the foramen magnum may have also contributed to obstruction of fourth ventricular outflow in both settings. This unusual case of acute onset IFV is presented in detail. The underlying etiologies and clinical settings in which IFV may develop is reviewed as well. Although the precise sequence of events leading to acute IFV cannot be resolved for this case, the importance of recognizing the potential for acute IFV following herniation is underscored.

Anatomic Variability of the Morphometric Parameters of the Fourth Ventricle of the Brain

“…The received data will help neurosurgeons to assess the diameters of the fourth ventricle in dynamics during the recovery of their patients after the operative treatment of the hydrocephalus, preventing severe complications of the shunt obstruction (e.g., cerebellar tonsillar herniation) on early stages. 17,18 In accordance with our findings, the diameters of the fourth ventricle correlate with the diameters of the skull, showing weak (skull length-anteroposterior diameter of the fourth ventricle and skull height-fourth ventricle height) and mild (skull width-fourth ventricle transverse diameter) positive correlation between these parameters.…”

Trapped Fourth Ventricle in Recurrent Acoustic Schwannoma - A Rarity

“…We believe that with the blockage of the aqueduct and basal cisterns, secondary to adhesions, the entry and exit pathways of the CSF are obstructed, thus causing fourth ventricular dilatation. 3,5,7 It is most often described in children, secondary to hydrocephalus caused by intraventricular hemorrhage, prematurity or infection. 8 It is also observed secondary to the functional occlusion of the aqueduct, often related to over-drainage with or without associated slit ventricles.…”

The isolated fourth ventricle

“…Closure of the fourth ventricular outlet isolates the fourth ventricle from the rest of the ventricular system; the choroid plexus in the fourth ventricle continues to produce CSF, leading to subsequent dilation of the fourth ventricle and progressive compression of the adjacent structures 8–10. Ataxia, nystagmus, dysartharia, pyramidal weakness, cranial nerve palsies, eye movement disorders and symptoms of increased intracranial pressure 6 11 12…”