Colloid Cysts Workup

Updated: Apr 17, 2016
  • Author: Lawrence S Chin, MD, FACS, FAANS; Chief Editor: Brian H Kopell, MD  more...
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Laboratory Studies

Routine preoperative studies, including a CBC count, chemistry panel, and coagulation studies are performed in addition to various imaging modalities.


Imaging Studies

CT scan

Colloid cysts appear homogeneous, with two thirds of them appearing hyperdense to the surrounding parenchyma and one third appearing isodense to the surrounding parenchyma. The lesions are well delineated and are usually round or ovoid. Occasionally, the lesions have a thin rim of enhancement after contrast injection, but they are typically nonenhancing and are not calcified. The size of these cysts varies, but most are 5-25 mm. [20]

Axial CT scan that shows a colloid cyst with assoc Axial CT scan that shows a colloid cyst with associated hydrocephalus.

The CT scan is an important preoperative study because the viscosity of the cyst contents correlates more closely to the radiodensity visible on a CT scan than to the density visible on MRI. The viscosity of cyst contents determines the most appropriate surgical approach. A hyperdense cyst is more likely to have solid contents and is more difficult to drain. Hyperdensity may also correlate with a reduced capacity to enlarge over time.


The appearances of colloid cysts on MRIs are variable. The most common appearance is hyperintensity on T1 and hypointensity on T2. The amount of rim enhancement is variable. The variable MRI signals do not correlate with the fluid density of cyst contents, although a MRI is valuable in differentiating a colloid cyst from a basilar tip aneurysm, which may a have similar appearance on a CT scan. [21, 22, 23, 20, 23]

Additionally, recognizing that a CSF flow artifact at the Monro foramen can mimic the appearance of a colloid cyst through MRI is important. Finally, the Constructive Interference in the Steady State (CISS) sequence of a MRI can delineate an abnormal contour of the ventricular system and intraventricular septa, from which essential information for surgical planning, including endoscopic surgery can be obtained. Postoperative CISS images can also be used, demonstrating not only regression of hydrocephalus but also the patency of small fenestrations.

In a retrospective study of 19 patients who underwent endoscopic management of colloid cysts of the third ventricle, El-Khoury et al found that 100% of lesions with low signal intensity on T2-weighted images had a higher intracystic viscosity contents that translated to an increased difficulty in aspiration of the contents. [24] In contrast, 63% of patients with high-signal lesions were easy to aspirate. This differentiation may be useful in preoperative planning and management.

A retrospective study of 25 patients who underwent colloid cyst excision found specific MRI features suggestive of difficult cyst excision. In a subgroup of patients with preoperative hydrocephalus and imaging features suggestive of difficult removal, significantly higher rates of shunting were observed. The authors suggest using an open approach in cases of low T2, high T1 signal cysts with a diameter of over 15 mm, or CSF shunting in poor surgical candidates. For smaller cysts with a low T1 signal, a high T2 signal, and preoperative hydrocephalus, the authors recommend endoscopic intervention as the procedure of choice. [23]

Coronal MRI shows a colloid cyst in the roof of th Coronal MRI shows a colloid cyst in the roof of the third ventricle. The patient has mild hydrocephalus.
Intraoperative photograph through the operating mi Intraoperative photograph through the operating microscope shows a colloid cyst in the Monro foramen. Choroid plexus is observed overlying the cyst, and the thalamostriate vein is along the inferior border.
Intraoperative photograph that shows removal of th Intraoperative photograph that shows removal of the cyst, leaving a dilated Monro foramen. The third ventricle can be seen through the opening.

Other Tests

Ophthalmologic evaluation may be useful if diplopia (seen in 10% of patients) is a presenting complaint or if papilledema (seen in 50% of patients) is found during the examination. Neuropsychological evaluation may be useful if memory loss or behavior change (found in 35-40% of patients) is a presentation.


Diagnostic Procedures

Lumbar puncture is typically contraindicated in patients with these lesions because of a risk of cerebral herniation in patients who demonstrate noncommunicating hydrocephalus.


Histologic Findings

Colloid cysts are lined with simple or pseudostratified epithelial cells. Their shape is either flattened cuboidal or low columnar, and they rest on a thin capsule of collagen and fibroblasts. The cysts are mucin secreting and ciliated. Cells are Periodic Acid-Schiff (PAS) and S100 positive, while Glial Fibrillary Acidic Protein (GFAP), vimentin, and neurofilament are negative. The stromal wall stains positively for vimentin. Contents of the cyst are usually greenish and of variable viscosity.