Colloid cyst

Findings

The CT of the paranasal sinus shows a circumscribed hyper dense homogenous mass at midline anterior to third ventricle. The MRI of the brain shows an approximately 1 cm circumscribed mass location as above. Isointense on T1. Iso/slight hyper intense on T2. Hyperintense on FLAIR. No diffusion restriction or enhancement. Some heterogeneity of inferior margin (seen on sagittal). There is hydrocephalus of the left lateral ventricle.

Differential diagnosis:
- Colloid cyst
- Pseudocyst (CSF flow artifact)
- Choroid plexus papilloma
- Glioma
- Hamartoma
- Neurocysticercosis
- Granulomatous disease


Diagnosis: Colloid cyst


Colloid cyst

Not a true neoplasm; rather a remnant from embryonic endoderm
Contains variable contents including mucinous secretions and desquamated epithelial cells. This variability accounts for variable MRI signal characteristic
Usually present in 3rd to 4th decade
2% of all intracranial masses, 15-20% of all intraventricular masses
Only 10% show growth
Classic clinical scenario is acute onset headache (duet to acute obstruction and hydrocephalus) which is reproduced with tilting head forward (Brun phenomenon)
Fatalities reported due to this lesion (though not common)


Radiologic overview of the diagnosis

The location of this lesion is nearly pathognomonic = Attached to anterior/superior 3rd ventricular roof, wedged into foramen of Monro, with pillars of fornix draped around cyst.
Variable size at presentation, mean size = 15 cm
May be associated with ventriculomegaly

CT:
- 2/3 hyper dense, 1/3 iso- to hypo- dense (dependent on hydration state)
- Usually no enhancement, rarely rim enhances

MRI:
- T1WI usually hyper intense (2/3), 1/3 isointense
- T2WI majority isointense, but more variable, reflects hydration content of internal materials
- Can see fluid-fluid levels
- FLAIR: Does not suppress (hyper intense)
- DWI: No restriction
- Rare rim enhancement