Fourth Ventricle Outlet Obstruction with Expanding Space on the Surface of Cerebellum.
BACKGROUND
Hydrocephalus is classified as noncommunicating and communicating based on whether all ventricular and subarachnoid spaces are communicating. Although the diagnosis between the two different states is crucial, it is difficult in certain conditions. In particular, communicating hydrocephalus and noncommunicating hydrocephalus owing to fourth ventricle outlet obstruction are highly misdiagnosed. We describe a case of fourth ventricle outlet obstruction of unknown origin that was initially misdiagnosed as communicating hydrocephalus.


METHODS
A 66-year-old woman with gait disturbance and incontinence caused by hydrocephalus underwent ventriculoperitoneal shunt surgery. After 9 months, her fourth ventricle became enlarged and could not be controlled by lowering the shunt pressure. Magnetic resonance imaging (MRI) demonstrated obstruction at the foramen of Magendie, foramina of Luschka, and the cerebral aqueduct. Endoscopic surgery for aqueduct plasty with third ventriculostomy was planned. Because the aqueduct was observed to open spontaneously, only the standard third ventriculostomy was performed. When MRI findings were reviewed retrospectively, an unnatural space was observed between the lower cranial nerves and cerebellar hemisphere that grew along with the fourth ventricular enlargement. This space was determined by MRI cisternography to be the cystic membrane ballooning out from the foramen of Luschka. The primary hydrocephalus likely resulted from fourth ventricle outlet obstruction.


CONCLUSIONS
Enlargement of the whole ventricular system with an expanded space between the lower cranial nerves and cerebellar hemisphere can be caused by fourth ventricle outlet obstruction. In such cases, preoperative evaluation of anatomic architecture and cerebrospinal fluid obstruction using MRI cisternography is essential and leads to a successful endoscopic strategy.
Department of Neurosurgery, Kesen-numa City Hospital, Miyagi, Japan; Department of Neurosurgery, Tohoku University Graduate School of Medicine, Sendai, Japan. Electronic address: yositeru8_8_8simoda@yahoo.co.jp.
Yoshiteru
Y
Shimoda
Department of Neurosurgery, Sendai Medical Center, Sendai, Japan.
Kensuke
K
Murakami
Department of Neurosurgery, Kesen-numa City Hospital, Miyagi, Japan.
Norio
N
Narita
Department of Neurosurgery, Tohoku University Graduate School of Medicine, Sendai, Japan.
Teiji
T
Tominaga
D000368:Aged; D002531:Cerebellum / Q000000981:diagnostic imaging*; D003951:Diagnostic Errors; D005260:Female; D020546:Fourth Ventricle / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D006849:Hydrocephalus / Q000000981:diagnostic imaging* / Q000209:etiology / Q000601:surgery; D008279:Magnetic Resonance Imaging; D044583:Neuroendoscopy; D017287:Ventriculoperitoneal Shunt; D014696:Ventriculostomy
Foramen of Luschka; Fourth ventricle; Hydrocephalus; Noncommunicating