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|Year : 2015 | Volume
| Issue : 5 | Page : 801-802
Tension arachnoid cyst with transtentorial herniation: A rare entity
Ankit Balani, Anjani D Kumar, Sapna S Marda, Surendar Alwala
Department of Radiology, Yashoda Hospital, Secunderabad, Telangana, India
|Date of Web Publication||6-Oct-2015|
Dr. Ankit Balani
61, Shyam Nagar, Pal Link Road, Jodhpur, Rajasthan
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Balani A, Kumar AD, Marda SS, Alwala S. Tension arachnoid cyst with transtentorial herniation: A rare entity. Neurol India 2015;63:801-2
A 70-year-old female patient presented to the emergency department of our hospital with complaints of multiple episodes of seizures followed by sudden onset loss of consciousness. There was a history of headache since 1 week with 2 episodes of vomiting. She was a known type II diabetic since 10 years, poorly compliant to oral hypoglycemic medication and also having diabetic nephropathy. Her neurological examination was unremarkable. Magnetic resonance imaging (MRI) of the brain revealed a large cerebrospinal fluid (CSF) signal intensity, extra-axial lesion in the right middle cranial fossa and right sylvian fissure causing buckling of the underlying brain parenchyma [Figure 1], [Figure 2], [Figure 3], [Figure 4] with mass effect in the form of subfalcine [Figure 1] and [Figure 2] as well as right transtentorial, and uncal herniation [Figure 3] and [Figure 4] with midline shift of 12 mm toward the left at the level of the third ventricle. There was no evidence of restriction of diffusion or blooming on gradient sequences. The imaging features suggested the diagnosis of a tension arachnoid cyst with transtentorial, uncal and subfalcine herniations. The patient was treated with a cystoperitoneal shunting and had a good recovery at follow up. The biochemical analysis of the cyst fluid revealed the total protein levels being 27 mg/dl.
|Figure 1: Axial T2-weighted magnetic resonance imaging of brain showing a large, well-defined, T2 hyperintense extra-axial lesion (white arrow) in the right sylvian fissure causing buckling of the underlying cortex and subfalcine herniation toward the left side|
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|Figure 2: Axial diffusion-weighted section of magnetic resonance imaging of the brain revealing a lesion that does not show restriction of diffusion (white arrow)|
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|Figure 3: Axial fluid-attenuated inversion recovery section of magnetic resonance imaging brain showing complete suppression of T2 hyperintense signal within the lesion (white arrow). There is right transtentorial and uncal herniation (white dashed arrow)|
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|Figure 4: Coronal T2-weighted magnetic resonance imaging of the brain showing the right sided transtentorial herniation (black arrow)|
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Arachnoid cysts are congenital benign cysts that occur both within an intracranial compartment (more common) and in the spinal canal. They arise due to the accumulation of CSF within the potential space due to congenital splitting of the arachnoid layer. They are usually small and asymptomatic; a few patients, however, present with neurological dysfunction due to the mass effect. A tension arachnoid cyst causing uncal herniation is an extremely rare entity and only a handful of case reports have been reported in literature., It is hypothesized that a “ball-valve” mechanism at a point within the cyst wall results in increased accumulation of fluid within, causing life-threatening mass effect in such cases., Similarly, one-way slit valves have been identified in the suprasellar prepontine arachnoid cysts and this is postulated to be the mechanism of cyst enlargement. Other mechanisms that have been postulated include active transport or secretion of molecules from the lining cells or fluid influx due to the osmotic pressure gradient. In our case, we failed to demonstrate a one-way slit valve, and biochemical analysis of the cyst fluid was comparable to that of CSF. Computed tomography (CT) features of an arachnoid cyst include a nonenhancing hypodense lesion, which may cause remodeling and scalloping of the overlying bone. CT cisternography may show late pooling of the contrast within the cyst and demonstration of its communication with the subarachnoid space. On MRI, the lesion shows CSF signal intensity on all sequences including fluid-attenuated inversion recovery and diffusion weighted image. There are no solid components, and the lesion shows no post-contrast enhancement. Treatment of symptomatic lesions includes a craniotomy (fenestration or excision), a cystoperitoneal shunt or an endoscopic fenestration.
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