A LARGE FOURTH VENTRICLE EPIDERMOID

CYSTBY

Dr.K.PRASANNAPOST GRADUATE STUDENT,

RAJAH MUTHIAH MEDICAL COLLEGE & HOSPITAL

(RMMCH),

ANNAMALAI UNIVERSITY, CHIDAMBARAM

CLINICAL HISTORY

51 year old male came with complaints of

chronic headache.

He had 3 episodes of generalized seizures.

There is weakness of all four limbs.

There is no history of fever, trauma.

Blood parameters were normal.

Patient was referred for MRI brain.

MRI

MR imaging of the brain revealed an extra-axial, lobulated ill

defined mass occupying the fourth ventricle with extension into

CP angle which is hypo intense on T1 & hyper intense on T2

insinuating the vessels around CP angle with no evidence 0f

blooming on gradient imaging with no enhancement in contrast.

The Fourth ventricle mass which is iso intense to

CSF in T1 & T2 is suppressed in FLAIR sequences.

The mass is causing mild dilatation of lateral

ventricles.

MRI

The lesion had homogeneous CSF intensity

on both T1-weighted and T2-weighted

images and remained hypo intense on

FLAIR sequences.

There is no evidence of any altered signal

intensity within the mass lesion.

EPIDERMOID CYST

Epidermoid cyst, or pearly tumour, is congenital in origin

and accounts for about 1% of intracranial tumours.

It is a benign extra cerebral intradural lesion and in about

40% of cases is located in the cerebellopontine angle.

They are believed to form between the 3rd and 5th week

of embryonic development as a result of displaced

epithelial remnants that remain after the neural tube

closes.

Although acquired epidermoid tumours may develop

as a result of trauma, this is uncommon in the brain.

Grossly, epidermoid tumors are typically well defined

lesions with an irregular nodular outer surface and a

shiny “mother of pearl” appearance.6,7

The cyst content is derived from desquamated

epithelial cells composed mainly of keratin in

concentric layers and cholesterol in a solid crystalline

state.1,4,7-9

EPIDERMOID CYST

On MR imaging, epidermoid tumours typically

have low signal intensity on T1-weighted images,

high signal intensity on T2-weighted images, and

no enhancement on gadolinium-enhanced images.

Epidermoid tumors showing unusual signal

intensity changes have been reported.1,7,10-

13

EPIDERMOID CYST

The tumour can be a so-called white epidermoid with

short T1 values and fatty attenuation on CT,

characterized surgically as being cystic and having a

high lipid content comprising mixed triglycerides

containing unsaturated fatty acid residues, and no

cholesterol. 11

It can show hyper intensity on T1- and T2-weighted

MR images, caused by a semi liquid cystic content

with high protein concentration.

EPIDERMOID CYST

The intra cystic haemorrhage can cause a high

signal intensity on both T1- and T2-weighted

images because of the paramagnetic effect of

heme iron (Fe3) in methemoglobin and other

haemoglobin breakdown products.

EPIDERMOID CYST

Differential diagnosis of EPIDERMOID CYST CSF collections, e.g. Arachnoid cyst or mega cisterna magna

Less lobulated follows CSF on all sequences, including FLAIR and DWI

Dermoid cyst

Often fat density due to sebum

Inflammatory cyst, e.g. Neurocysticercosis

Smaller, but may be multiple

May enhance peripherally

May have associated oedema

Usually no restricted disffusion

Cystic tumour, e.g. Acoustic schwannoma or craniopharyngioma

Solid enhancing component is usually identifiable

Neurenteric cyst

Epidermoid cysts typically show undulating margins and

model their shape to conform to the cerebropontine

angle.

The cyst has a tendency to insinuate itself around the

nerves and blood vessels in the cerebropontine angle.

They usually do not enhance with gadolinium and do not

bleed.

From a practical point of view, recognition of case as a

hemorrhagic epidermoid cyst is important.

References Mohanty A, Venkatrama SK, Rao BR, et al. Experience with

cerebellopontine angle epidermoids. Neurosurgery 1997;40:24–30 .Tampieri D, Melanson D, Ethier R. MR imaging of epidermoid cysts.

AJNR Am J Neuroradiol 1989;10:351–56 Gao PY, Osborn AG, Smirniotopoulos JG, et al. Radiologic-pathologic

correlation: epidermoid tumor of the cerebellopontine angle.AJNRAmJ Neuroradiol 1992;13:865–72

Salazar J, Vaquero J, Saucedo G, et al. Posterior fossa epidermoid cysts. Acta Neurichir 1987;85:34–39

de Souza CE, deSouza R, Costa SD, et al. Cerebellopontine angle epidermoid cysts: a report on 30 cases. J Neurol Neurosurg Psychiatry 1989;52:986–90

Ochi M, Hayashi K, Hayashi T, et al. Unusual CT and MR appearance of an epidermoid tumor of the cerebellopontine angle. AJNR Am J Neuroradiol 1998;19:1113–15