COLLOID CYST OF THE THIRD VENTRICLE: REPORT OF TWO CASES NR 32 COLLOID CYST OF THE THIRD VENTRICLE: REPORT OF TWO CASES N. EZZAAIRI, M. MAATOUK, M.A. JELLALI, W.MNARI, A. ZRIG, W. HARZALLAH, R.SALEM, M. GOLLI Service d’imagerie médicale, CHU Fattouma Bourguiba Monastir –TUNISIE

Introduction Colloid cysts (CC) are relatively rare intracranial benign congenital tumors accounting for 0.5%–1% of primary brain tumors and 15%–20% of intraventricular masses. Colloid cysts are slowly growing non-neoplastic cysts that are predominantly arising in the anterior region of the 3rd ventricle (more than 99%). They are classically presenting during the 3rd to 4th decades.

Introduction Typically, patients are asymptomatic, although colloid cysts may cause symptoms by obstructing the foramen of Monro. Both magnetic resonance imaging (MRI) and computed tomography (CT) can be used for the diagnosis.

Case report In this report, we present 2 cases of CC of the 3rd ventricle, along with the findings of radiological imaging.

Patient one A 57-year-old man, admitted following head injury. A unenhanced CT scan (NECT) did not demonstrate any intracranial hemorrhage but there hyperdense foramen of Monro mass.

B D A C E MRI confirmed the presence of a small colloid cyst at the foramen of Monro which was homogeneously hyperintense to brain on T1 WI (B). T2WI (C) shows a mixed signal mass with a focus of profound hypointensity. FLAIR sequence (D) shows the cyst does not suppress. There was no restriction in DWI (E)

Patient 2 A 48-year-old man presented to the emergency department, with a 2 day history of frontal headache and nausea associated with an episode of vomiting. He was neurologically intact, with no signs of meningism.

NECT shows a small, Well-demarcated round, hyperdense foramen of Monro mass with obstructive hydrocephalus. There was no enhancement after injection.

B D A C MRI imaging shows a colloid cyst at the foramen of Monro (A). The cyst is hyperintense on T1 WI (B) and is causing moderate hydrocephalus with transependymal CSF flow (C). T1WI with gadolinium revealed no enhancement (D).

Discussion Colloid cyst or paraphyseal cyst is the most common tumours in the 3rd ventricle. It’s wedged into foramen of Monro in over 99% of cases. Rare reports describe other locations including the leptomeninges, cerebellum, lateral and 4th ventricles. CC, like neurenteric and Rathke cysts, is derived from embryonic endoderm.

Discussion Age : 3rd to 4th decade Rare in children 40-50% asymptomatic, discovered incidentally The most common sign is a headache (50-60%) Acute foramen of Monro obstruction may lead to rapid onset hydrocephalus, herniation and death

Discussion Prognosis is variable: Criteria of poor prognosis are: 90% of CC are stable 10% can expand rapidly, causing coma and death. Criteria of poor prognosis are: Younger patients Larger cyst, hydrocephalus Iso/hypodense on NECT, often hyperintense on T2WI

Pathologic findings CC is a smooth, spherical, well-delineated cysts. The content is composed of a viscous gelatinous material (colloid) with variable viscosity. Histologically, CC is characterized by a simple or pseudostratified epithelial lining with interspersed goblet cells and scattered ciliated cells. The cyst contents is PAS positive and composed of. It may contain necrotic leucocytes and cholesterol clefts.

Imaging Either CT or MRI may help in diagnosing a CC, although MRI has a few advantages. The multiplanar capabilities of MRI optimally demonstrate the classical location of the cyst, and typical signal intensities in the cyst help helpful in the early and correct diagnosis of this entity.

Imaging : CT On NECT, approximately 2/3 of CC are slightly hyperdense. It may occasionally be hypodense or isodense. The density is correlated inversely with hydratation state. Calcification or hemorrhage are rare. After administration of iodinated contrast material, no enhancement of the mass lesion or a thin rim of enhancement may be present.

Imaging : MRI On T1WI, the signal of CC is correlates with cholesterol concentration: 2/3 are hyperintense 1/3 are isointense On T2 WI, the signal is more variable: the majority are isointense to brain. ¼ are mixed  “black hole” effect On FLAIR sequence; the signal cyst is not suppressed There are not restriction on DWI

Differential diagnosis The imaging appearance of a colloid cyst is almost pathognomonic. The most common “lesion” mistaken for a colloid cyst is CSF flow artifact (MR pseudocyst) caused by pulsatile turbulent CSF flow around the foramen of Monro. Multiplanar technique confirms artifact.

Differential diagnosis Occasionally, a neurocysticus cyst may occur at the foramen of Monro. However, multiple lesions within parenchyma and cisterns are usually shown in neurocysticercosis. Neoplasms such as subependymoma or choroid plexus papilloma that may occur at the foramen of Monro are much less common and typically enhanced.

Treatement Prophylactic surgery for asymptomatic CC of the 3rd ventricle remains controversial. However, the possibility of spontaneous rupture of these cysts should also be kept in mind. The most common treatment consist on complete surgical resection. Recurrence is rare, if resection is complete