IS Case 424: Colloid cyst
Imaging Sciences URMC 2010
Publication Date: 2010-08-27
A 60-year-old male presented with several days of lightheadedness and near syncope when waking. Patient also noted a low-grade headache. Physical exam was within normal limits and neurology exam was normal.
CT scan showed a hyperdense, well-circumcised lesion in the superior aspect of the third ventricle at the Foreman of Monro. Mild hydrocephalus was noted (Figs. 1 & 2). MRI demonstrated a hyperintense lesion on T1 and an isointense lesion on T2 with a halo of hyperdensity at the Foreman of Monro which does not suppress on FLAIR. This is shown on axial, coronal and sagittal images. Hydrocephalus is present (Figs. 3–8). These finding suggest a mucin containing cyst consistent with a colloid cyst.
Colloid cysts are diagnosed in 3/1,000,000 cases per year. They are benign and represent 0.5%-1.0% of primary brain tumors. There is no gender predominance and usually patients are in their third to fourth decade of life when a colloid cyst is first diagnosed.
The origin of the colloid cyst is highly debated with most believing that it originates from the neuroendoderm. It is found in the superior aspect of the third ventricle at the Foramina of Monro in 99% of the cases. They are composed of a simple or pseudostratified lining and mucous goblet cells which account for the hyperintensity on imaging. The average size of a colloid cyst is 15 mm with a range of 3–40 mm. Due to their location they commonly obstruct the Foramina of Monro, thus causing the patient's symptoms.
Patients normally present with positional headaches (50-60%) due to ventricle dilation and thus increased CSF. Nausea and vomiting may also occur. It has been reported that patient's have experienced loss of consciousness ("drop attacks") and dementia. Rarely patients will present due to sudden death because of severe hydrocephalus and brain herniation.
Imaging shows a high attenuation lesion on non-contrast CT due to increased cholesterol, this occurs in 2/3 of the cases with calcification being extremely rare. Sometimes a colloid cyst can appear hypodense or isodense, however usually they are found to be hyperdense and non-enhancing post-contrast. Obstructive hydrocephalus is commonly seen and in severe cases patients can present with sudden death. An MRI more commonly shows a hyperintense lesion on T1 and an isointense lesion on T2. A colloid cyst is commonly ring enhancing on T2 due to the pseudostratified epithelium.
It has been suggested that the intensity on CT and MRI can help determine the efficacy of stereotatic aspiration. Commonly a cyst containing less mucous is easier to drain due to lower viscosity and appears hypodense on CT, thus imaging can help determine what mode of treatment would be most beneficial for the patient. Complete resection of a colloid cyst is also preformed with 0% reoccurrence rate, however residual cyst will cause reoccurrence in 10% of cases. The prognosis of a colloid cyst is very good with an early diagnosis.
- Armao D, Castillo M, Chen H, Kwock L. Colloid cyst of the third ventricle: imaging-pathologic correlation. AJNR Am J Neuroradiol. 2000 Sep;21(8):1470-7. PMID: 11003281
- Osborn AC. Diagnostic Neuroradiology. Mosby-Year Book, Inc. 1994; 639-642.