Idiopathic unilateral hydrocephalus

Clinical History

19-year-old female patient presented with a long history of headaches. Clinical examination which included a full neurological assessment was unremarkable. No relevant previous medical history was elicited.

Imaging Findings

CT brain (Fig. 1 and 2) shows marked asymmetrical dilatation of the right lateral ventricle. The left lateral ventricle, third and fourth ventricles were normal.
T2-weighted MR (Fig. 3 and 4) and FLAIR images (Fig. 5 and 6) demonstrate normal adjacent brain parenchyma. No adjacent parenchymal gliosis or transependymal CSF spread is seen. Specifically there is no obstructing mass lesion at the level of the foramen of Monroe. Contrast was not administered as the patient had given a history of failure.

Discussion

Background:
Unilateral hydrocephalus results from obstruction of the foramen of Monroe resulting in asymmetrical dilatation of the lateral ventricle¹. Etiological factors are often divided into two main groups namely
(a) congenital (atresia of the foramen of Monroe) and
(b) acquired including neoplastic obstruction, vascular anomalies, post inflammatory gliosis (following a history of meningitis or ventriculitis), ependymal cysts, and iatrogenic causes such as post shunting [2]. The list is not exhaustive and sometimes an underlying cause cannot be identified and hence it is classified as idiopathic [1]. Congenital forms occur almost exclusively in children, while the acquired forms present later, including in adult life. Idiopathic unilateral hydrocephalus is a rare entity in adults, and only a couple of cases have been reported in the literature.

Clinical Perspective:
Headache is the most common symptom [1]. Visual disturbances, dizziness, seizures, cognitive changes, signs of raised intra-cranial pressure [2] and focal neurological signs have all been associated with the condition. Unilateral hydrocephalus is often an unexpected imaging finding. MRI may be indicated as it may reveal the underlying aetiology, and contrast is routinely administered to outrule an underlying tumour.

Imaging Perspective:
Unilateral hydrocephalus can be diagnosed pre- and peri-natally by ultrasound [3]. In adults CT is often the first line imaging [4]. Contrast enhanced MR is often required to outrule causative findings. Endoscopic inspection is a consideration as it may help guide treatment options.

Outcome:
Treatment options and prognosis depend on the underlying aetiology. Fenestration of the septum pellucidum (via neuroendoscopic/stereotactic techniques or open craniectomy) is the preferred surgical option [2] for idiopathic unilateral hydrocephalus. Ventriculo-peritoneal shunting is an option when fenestration fails to relieve hydrocephalus. Presumed idiopathic cases are sometimes found to have atresia or a web of ependyma across the foramen of Monroe. Patients often return to be symptom free after resolution of hydrocephalus [5]. In the congenital variant, early diagnosis and treatment often result in a favourable outcome [3].

Take Home Message, Teaching Points:
Idiopathic unilateral hydrocephalus is a rare entity. Clinical history and imaging are essential to exclude an underlying tumour and previous infections, which are by far commoner causes of asymmetrical hydrocephalus. Contrast enhancement is required unless contraindicated.

Differential Diagnosis:
1) Acquired unilateral hydrocephalus
2) Ipsilateral haemispheric hypoplasia / atrophy

Differential Diagnosis List

Final Diagnosis

Idiopathic unilateral hydrocephalus

URL:	https://www.eurorad.org/case/8708
DOI:	10.1594/EURORAD/CASE.8708
ISSN:	1563-4086