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Colloid Cyst


KEY FACTS

Terminology

  • Unilocular mucin-containing 3rd ventricular cyst

Imaging

  • > 99% are wedged into foramen of Monro

    • Pillars of fornix straddle, drape around cyst

    • Majority are hyperdense on NECT

    • Density correlates inversely with hydration state

  • MR signal more variable

    • Generally reflects water content

    • Majority isointense to brain on T2WI (small cysts may be difficult to see)

    • 25% mixed hypo/hyper (“black hole” effect)

    • May show mild rim enhancement (rare)

Top Differential Diagnoses

  • Neurocysticercosis

  • Cerebrospinal fluid flow artifact (MR pseudocyst)

  • Vertebrobasilar dolichoectasia/aneurysm

  • Subependymoma

  • Craniopharyngioma

Pathology

  • From embryonic endoderm, not neuroectoderm

  • Similar to other foregut-derived cysts (neurenteric, Rathke)

Clinical Issues

  • 40-50% asymptomatic, discovered incidentally

  • Headache (50-60%; can be periodic, intermittent)

    • Acute foramen of Monro obstruction may lead to rapid onset hydrocephalus, herniation, death

  • Peak age = 3rd to 4th decade (rare in children)

  • 90% stable or stop enlarging

  • 10% enlarge

Diagnostic Checklist

  • Beware of flow artifact in 3rd ventricle mimicking colloid cyst

Axial graphic shows a classic colloid cyst at the foramen of Monro causing mild/moderate obstructive hydrocephalus. Note that the fornices and choroid plexus are elevated and stretched over the cyst
.

Axial gross pathology in a patient who suddenly and inexplicably died shows a large colloid cyst
causing moderate obstructive hydrocephalus. A small cavum septi pellucidi is present. Fornices
are draped over the cyst.

(Courtesy R. Hewlett, MD.)

Axial NECT in a 65-year-old man with “thunderclap” headache, obtained to look for a subarachnoid hemorrhage, shows a classic colloid cyst, seen here as a hyperdense mass
wedged into the foramen of Monro and upper 3rd ventricle.

Sagittal T2WI MR in the same patient shows the mass
to be very hypointense, indicating inspissated proteinaceous contents. Note the markedly enlarged lateral ventricle with a normal-sized 3rd ventricle. The colloid cyst was removed emergently.

TERMINOLOGY

Abbreviations

  • Colloid cyst (CC)

Synonyms

  • Paraphyseal cyst, endodermal cyst

Definitions

  • Unilocular, mucin-containing 3rd ventricular cyst

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