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Unilateral ventricular entrapment in acute cerebral oedema and increased intracranial pressure: An imaging cascade framework
*Corresponding author: Pratiksha Baliga, Department of Neurosurgery Research, Mahatma Gandhi Mission Institute Of Health Sciences, Mumbai, Maharashtra, India drpratikshabaliga@gmail.com
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Received: ,
Accepted: ,
How to cite this article: Moscote-Salazar LR, Janjua T, Baliga P, Agrawal A. Unilateral ventricular entrapment in acute cerebral oedema and increased intracranial pressure: An imaging cascade framework. South Asian J Health Sci. doi: 10.25259/SAJHS_12_2026
Dear Editor,
Segmental hydrocephalus with unilateral ventricular entrapment is an unusual condition that presents difficult diagnostic and management issues and can be observed in severe cases of acute neurological disease, such as malignant middle cerebral artery infarction, intracerebral hematoma, or traumatic brain injury.[1,2] It is characterised by the nonspecific dilatation of a single lateral ventricle, with obstructive and flow changes in cerebrospinal fluid (CSF), usually leading to acute cerebral oedema and raised intracranial pressure (ICP).[1,2] These imaging findings—unilateral ventricular entrapment, asymmetric ventricular dilatation, foramen of Monro obstruction, unilateral cerebral oedema, signs of intracranial pressure rise, and altered CSF dynamics-represent a structured radiological cascade reflecting progressive pathophysiologic changes in segmental hydrocephalus rather than independent diagnostic variables. These features occur sequentially, beginning with mechanical obstruction, followed by altered CSF flow, ventricular enlargement, parenchymal oedema, and finally localised intracranial pressure elevation. We therefore describe this pattern as an imaging cascade to aid recognition of disease progression and guide timely intervention.
Although fluid-attenuated inversion recovery (FLAIR) hyperintensity is observed across oedema, periventricular seepage, and CSF stasis, these findings represent involvement of distinct anatomical compartments: parenchymal tissue, periventricular white matter, and ventricular CSF reflecting escalating pressure states rather than redundant imaging markers.
Stage 1: Foramen of Monro obstruction
In addition to the unilateral form, another key requirement as a diagnostic criterion for the diagnosis of unilateral ventricular entrapment is obstruction of the foramen of Monro.[3] This obstruction halts the usual CSF flow from the lateral ventricle to the third ventricle, leading to the characteristic findings in segmental hydrocephalus. Imaging studies (both contrast-enhanced magnetic resonance imaging (MRI) and cine-MRI) can show the absence of CSF flow through the foramen, which can be seen as a block at the junction between the lateral and third ventricles.[2,4,5] This lack of flow points towards a mechanical obstruction, which further confirms the diagnosis of unilateral ventricular entrapment.
Stage 2: Disruption of CSF flow
The fifth criterion involves the disturbance of normal CSF flow in the affected ventricle. Cine-MRI sequences can be particularly valuable in visualising the absence of CSF motion, which is typical of the trapped ventricle syndrome. This absence of flow can be referred to as the “CSF trapped sign,” appearing as a hyperintense signal on FLAIR imaging. This alteration of the flow dynamics is one of the primary signs of the obstruction at the foramen of Monro and the abnormal distribution of CSF in the ventricular system.
Stage 3: Asymmetric ventricular dilatation
One of the distinctive features of unilateral ventricular entrapment is the asymmetric dilatation (to maintain consistency with earlier usage) of the lateral ventricles.[1] The affected ventricle, or “trapped ventricle,” undergoes disproportionate enlargement compared to the contralateral ventricle.[2] A thin periventricular cortex over the involved side of the affected ventricle may be present along with this dilatation.[2] This feature is particularly well-seen on computed tomography and MRI imaging, where there is visualisation of a contrast difference between the two ventricles, signalling an impedance to normal drainage of CSF. It should be clearly distinguished from the other forms of hydrocephalus, which may present as bilateral ventricular dilatation, as this unilateral nature is a valuable pointer towards diagnosis.
Stage 4: Unilateral cerebral oedema or mass effect
The third criterion is the presence of unilateral cerebral oedema, which may be observed as areas of increased signal intensity on T2-weighted MRI and FLAIR images. The oedema may be vasogenic or cytotoxic, reflecting the underlying pathophysiological mechanisms responsible for brain swelling.[6] The trapped ventricle side typically shows a shift of the midline structures, with partial or total collapse of the opposite ventricle. There is also compression of the basal cisterns or the third ventricle, indicating an effect of mass due to increasing pressure within the trapped ventricle. These are also consistent with the diagnosis of increased ICP and highlight the necessity of an emergency intervention.
Stage 5: Localised signs of increased intracranial pressure
Localised signs of increased intracranial pressure are an important part of the diagnostic puzzle. Periventricular hyperintensity on T2/FLAIR sequences may be a sign of CSF transudation, a sign that the brain tissue is being compressed by the rising pressure in the trapped ventricle. As the condition progresses, this may lead to subalpine or trans tentorial herniation, both crucial findings that demand immediate consideration. Prompt identification of these findings can help clinicians determine the emergent nature of surgery, for example, the need for ventriculostomy or decompression.
In summary, imaging studies are highly relevant in identifying unilateral ventricular entrapment and demonstrate a predictable radiological cascade beginning with foramen of Monro obstruction and progressing through CSF flow disruption, asymmetric ventricular dilatation, cerebral oedema, and localised intracranial pressure rise.[1,2,4,5] Recognition of this sequential imaging framework assists clinicians in staging disease severity and facilitates timely intervention, such as ventriculostomy or decompression.
Author’s contributions:
PB, AA, LRMS: Conceptualization; TJ: Data curation; LRMS: Formal analysis, methodology; AA: Project administration; TJ: Visualization; PB, AA, LRMS: Writing – original draft; PB: Writing – review & editing.
Ethical approval:
Institutional Review Board approval is not required.
Declaration of patient consent:
Patient's consent not required as there are no patients in this study.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript, and no images were manipulated using AI.
Financial support and sponsorship: Nil.
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