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Colloid Cyst (CC)

Last Updated: March 27, 2020

Figure 1: Because colloid cysts are typically filled with a highly proteinaceous fluid, they are often dense on CT (top row left) and hyperintense on T1WI (top row right). Colloid cysts should have no internal enhancement on T1WI post contrast images (bottom). This colloid cyst is in the classic location at the foramen of Monro.

Figure 2: Sagittal (top row left) and axial (top row right) T1 images demonstrate a low signal intensity colloid cyst at the foramen of Monro. The cyst has a central T1 hyperintense focus that represents inspissated proteinaceous debris. The cyst is bright on T2 with low signal intensity proteinaceous debris that is sometimes referred to as the “black hole” effect (middle row left). The cyst remains predominantly hyperintense on FLAIR, indicating its content dissimilarity from CSF (middle row right). This cyst has no appreciable enhancement on post-contrast imaging (bottom row), with its only hyperintense component being the intrinsically T1 hyperintense debris centrally. Obstructive hydrocephalus is present on these images, a known common risk of colloid cyst due to their position. Incidentally, the internal proteinaceous debris is mobile in this cyst, indicated by its change from a central position on the earlier sequences (top row left, top row right, middle row right) to a right posterior position on the later sequences (middle row left and bottom row).

Basic Description

  • Mucin-containing, unilocular third ventricular cyst often located near the foramen of Monro
  • Synonymous terms: paraphyseal or neuroendodermal cyst


  • Congenital abnormality due to ependymal encystment or persistence of the paraphysis
  • Thin fibrous capsule of simple or pseudostratified epithelium with goblet and ciliated cells
  • Center filled with mucin, cholesterol, and desquamated epithelium

Clinical Features

  • Most common during 3rd and 4th decades of life
  • Uncommon in children
  • No gender predilection
  • Majority stable in size and without ventricular obstruction
  • Minority of cases continue to enlarge causing intraventricular obstructive hydrocephalus ± coma, death
  • Common presenting signs/symptoms
    • Small cysts: positional headache
    • Larger obstructing cysts: sudden-onset hydrocephalus with herniation, coma, and sudden death
  • Treatment: surgical resection, CSF shunting

Imaging Features

  • General
    • Well-marginated hyperdense unilocular cyst arising within anterior 3rd ventricle near the foramen on Monro (99%)
    • Forniceal pillars elevated over cyst
    • Size variable
    • ± Hydrocephalus
  • CT

    • Majority are hyperdense due to high proteinaceous content
    • No enhancement on contrast-enhanced CT
  • MRI

    • T1WI: Iso- to hyperintense due to cholesterol content
    • T2WI: Variable signal intensity
    • FLAIR: Hyperintense
    • DWI: No diffusion restriction
    • T1WI+C: No enhancement

Imaging Recommendations

  • Nonenhanced head CT, MRI without and with IV contrast (to exclude mimics); serial imaging follow-up for small cysts without hydrocephalus

For more information, please see the corresponding chapter in Radiopaedia.

Contributor: Rachel Seltman, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.01.08


Demirci S, et al. Sudden death due to a colloid cyst of the third ventricle: report of three cases with a special sign at autopsy. Forensic Sci Int. 2009;189:e33-36.

El Khoury C, et al. Colloid cysts of the third ventricle: are MR imaging patterns predictive of difficulty with percutaneous treatment? AJNR Am J Neuroradiol. 200021:489-492.

Osborn A G, Salzman KL, Jhaveri MD. (2016). Diagnostic Imaging (3rd ed). Philadelphia, PA: Elsevier, 2016.

Sheikh AB, et al. Endoscopic versus microsurgical resection of colloid cysts: a systematic review and meta-analysis of 1,278 patients. World Neurosurg. 2014;82:1187-1197.

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