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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) - Rare: Fluid-fluid or blood-fluid level (cyst "apoplexy")
Top Differential Diagnoses
- Neurocysticercosis
- Cerebrospinal fluid flow artifact (MR "pseudocyst")
- Vertebrobasilar dolichoectasia (VBD)/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%) - Acute foramen of Monro obstruction may lead to rapid-onset hydrocephalus, herniation, death
- Peak age = 3rd to 4th decades (rare in children)
- 90% stable or stop enlarging
- 10% enlarge
Diagnostic Checklist
- Beware of flow artifact in 3rd ventricle mimicking colloid cyst

TERMINOLOGY

Abbreviations
- Colloid cyst (CC)
Synonyms
- Paraphyseal cyst, endodermal cyst
Definitions
- Unilocular, mucin-containing 3rd ventricular cyst

IMAGING

General Features

Best diagnostic clue

- Hyperdense foramen of Monro mass on NECT

Location

- > 99% are wedged into foramen of Monro
        - Attached to anterosuperior 3rd ventricular roof
        - Pillars of fornix straddle, drape around cyst
        - Posterior part of frontal horns splayed laterally around cyst
- < 1% found at other sites
        - Lateral, 4th ventricles
        - Extraventricular CCs (very rare)
                  - Parenchyma (cerebellum)
                  - Extraaxial (prepontine, meninges, olfactory groove)

Size

- Variable (few mm to 3 cm)
- Mean: 15 mm

Morphology

- Well-demarcated round > ovoid/lobulated mass

CT Findings

NECT

- Density correlates inversely with hydration state
        - 2/3 hyperdense
        - 1/3 iso-/hypodense
- ± hydrocephalus
- Rare
        - Hypodense
        - Change in density/size

CECT

- Usually does not enhance
- Rim enhancement (rare)

MR Findings

T1WI

- Signal correlates with cholesterol concentration
        - 2/3 hyperintense on T1WI
        - 1/3 isointense
                  - Small CCs may be difficult to see
- May have associated ventriculomegaly

T2WI

- Signal more variable
        - Generally reflects water content
        - Majority isointense to brain on T2WI
                  - Small CCs may be difficult to see
- Less common findings
        - 25% mixed hypo/hyper ("black hole" effect)
- Rare
        - Fluid-fluid or blood-fluid level (cyst "apoplexy"), Ca⁺⁺ rare

FLAIR
```
- Does not suppress
```
DWI
```
- Does not restrict
```

T1WI C+

- Usually no enhancement
- Rare: May show peripheral (rim) enhancement

MRS
```
- Normal brain metabolites absent
```

Imaging Recommendations

Protocol advice

- NECT + contrast-enhanced MR
- ± serial imaging for asymptomatic cysts < 1 cm, no hydrocephalus

DIFFERENTIAL DIAGNOSIS

Neurocysticercosis
- Multiple lesions within parenchyma and cisterns
- Associated ependymitis or basilar meningitis common
- Ca⁺⁺ common
- Look for scolex
Cerebrospinal Fluid Flow Artifact (MR "Pseudocyst")
- Multiplanar technique confirms artifact
- Look for phase artifact
Vertebrobasilar Dolichoectasia/Aneurysm
- Extreme vertebrobasilar dolichoectasia (VBD) can cause hyperdense foramen of Monro mass
- Look for flow void, phase artifact on MR
Neoplasm
- Subependymoma - Frontal horn of lateral ventricle - Attached to septum pellucidum - Patchy/solid enhancement
- Craniopharyngioma - 3rd ventricle rare location - Usually not wedged into foramen of Monro, fornix - Ca⁺⁺, rim/nodular enhancement common
- Pituitary adenoma - Rare in 3rd ventricle - Enhances (usually strongly, uniformly)
Choroid Plexus Mass
- Choroid plexus papilloma - Rare in 3rd ventricle - Tumor of early childhood
- Xanthogranuloma - Rare in 3rd ventricle - Ovoid > round - Can be hyper- or hypodense ± Ca⁺⁺ - Can obstruct foramen of Monro - Can be indistinguishable on imaging studies
- Choroid plexus cyst - Usually found in infants - Anechoic at ultrasound

PATHOLOGY

General Features

Etiology

- From embryonic endoderm, not neuroectoderm
        - Similar to other foregut-derived cysts (neurenteric, Rathke)
        - Ectopic endodermal elements migrate into embryonic diencephalic roof
- Contents accumulate from mucinous secretions, desquamated epithelial cells

Genetics

- None known, but familial CCs represent 5-25% of cases
        - Patients often younger, more symptomatic

Associated abnormalities
```
- Variable hydrocephalus
```

Gross Pathologic & Surgical Features
- Gross appearance, location virtually pathognomonic - Smooth, spherical/ovoid well-delineated cyst - Thick gelatinous center, variable viscosity (mucinous or desiccated) - Rare = evidence for recent/remote hemorrhage
Microscopic Features
- Outer wall = thin fibrous capsule
- Inner lining - Simple or pseudostratified epithelium - Interspersed goblet cells, scattered ciliated cells - Rests on thin connective tissue layer
- Cyst contents - PAS + gelatinous ("colloid") material - Variable viscosity - ± necrotic leukocytes, cholesterol clefts
- Immunohistochemistry - ± epithelial antigen reactivity (cytokeratins, EMA) - Neuroepithelial markers negative
- Electron microscopy - Resembles mature respiratory epithelium - Nonciliated or tall columnar cells - Basal cells contain dense core vesicles

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Headache (50-60%)
- Less common = nausea, vomiting, memory loss, altered personality, gait disturbance, visual changes
- Acute foramen of Monro obstruction may lead to rapid onset hydrocephalus, herniation, death
- 40-50% asymptomatic, discovered incidentally
        - 5-15% 5-year risk of future progression necessitating operative intervention

Clinical profile
```
- Adult with headache
```

Demographics

Age

- 3rd to 4th decades
        - Peak: 40
        - Rare in children (only 8% < 15 at diagnosis), but may have precipitous symptoms, rapid deterioration

Sex
```
- M = F
```

Epidemiology

- 0.5-1.0% primary brain tumors
- 15-20% intraventricular masses
- Few familial cases reported

Natural History & Prognosis
- Varies with presence/rate of growth, development of cerebrospinal fluid (CSF) obstruction - Colloid Cyst Risk Score (CCRS) - 5-point measure to predict symptomatic clinical status, stratify risk for hydrocephalus - Age < 65 years; headache, cyst ≥ 7 mm, FLAIR hyperintense, anatomic risk zone (I-III from front to back of 3rd ventricle) - CCRSs 2 to 5 = 13% → 100% symptomatic, 8% → 83% develop hydrocephalus
- Prognosis excellent when CCs diagnosed early and excised
- 90% stable or stop enlarging - Older age - Small cyst - No hydrocephalus - Hyperdense on NECT, hypointense on T2-weighted MR
- 10% enlarge - Younger patients - Larger cyst, hydrocephalus - Iso-/hypodense on NECT, often hyperintense on T2WI - May enlarge rapidly, cause coma/death
- Rare: Hemorrhage with cyst "apoplexy"
- Rare: Regression
Treatment
- Most common = complete surgical resection - Neuronavigation-guided endoscopic removal + capsule coagulation - 50% experience short-term memory disturbance (usually resolves) - Recurrence rare if resection complete
- Options - Stereotactic aspiration (difficult with extremely viscous/solid cysts) - Imaging features that may predict difficulty with percutaneous therapy - Hyperdensity on CT/hypointensity on T2WI suggest high viscosity - Ventricular shunting - Observation (rare; not recommended, as sudden obstruction can occur with even small CCs)

DIAGNOSTIC CHECKLIST

Consider
- Consider CT or MR in patient with longstanding history of intermittent headaches
- Notify referring MD immediately if CC identified (especially if hydrocephalus is present)
Image Interpretation Pearls
- Beware of flow artifact in 3rd ventricle mimicking CC

9c1df1e2-4144-4a0c-a69c-edfe7c96a862

References

Selected References

Cases

{'cases': [{'authors': [{'key': 'c313fa7b-5bff-4b39-a8cd-dcf06aa6a69d', 'value': 'A. Carlson Merrow, Jr., MD, FAAP'}], 'caseVersionId': '0409292b-c233-4dfc-a50c-5b0de33b09ea', 'description': 'Axial NECT (#1), axial T1WI MR (#2), and sagittal T2* GRE MR (#3) show a small round mass (arrows) at the midline between the lateral ventricles near the foramina of Monro. The mass is hyperdense on CT (#1), bright on T1WI MR (#2), and isointense to white matter on T2* GRE MR (#3).', 'history': 'Headaches.', 'imagePoolId': '493e74df-8b88-47b5-bee3-cb786777b12c', 'name': 'Small hyperdense cyst', 'teachingPoint': 'This mass has typical signal characteristics and location for a colloid cyst.', 'demographics': '17 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '60b6667a-1c5a-45c6-8437-5a8e1a9ead33', 'description': "Axial NECT scan (#1) shows a small round hyperdense mass at the foramen of Monro (arrow). The lateral ventricles are moderately enlarged for the patient's age.\n\nThe lesion (arrows) appears hyperintense on sagittal (#2) and axial (#3) T1WIs. The mass is hypointense on T2WI (arrow, #4) and FLAIR (arrow, #5). While the ventricles appear moderately enlarged, there is no evidence for transependymal migration of CSF that would indicate acute obstructive hydrocephalus. T1 C+ FS scan (#6) shows the internal cerebral veins (arrows) and fornices (open arrows) are splayed around the mass.", 'history': 'Intermittent headache, ataxia.', 'imagePoolId': '96bb1dbd-0c3a-4afa-8bdb-d449ed8c934c', 'name': 'Small; hypointense on T2WI', 'teachingPoint': 'This is a classic colloid cyst in the classic location (99% are wedged into the foramen of Monro). The patient probably had intermittent obstruction of the foramen of Monro, accounting for the waxing and waning symptoms. The "black hole" effect (hypointensity on T2WI) correlates with desiccation and high viscosity, making cysts with this imaging finding difficult to aspirate. A colloid cyst was removed at surgery via transcallosal approach.', 'demographics': '43 Years old male'}, {'authors': [{'key': 'c313fa7b-5bff-4b39-a8cd-dcf06aa6a69d', 'value': 'A. Carlson Merrow, Jr., MD, FAAP'}], 'caseVersionId': '96b87d1b-d3ec-46eb-b2c3-438d5e9d8c02', 'description': 'Axial NECT (#1) shows a round hyperdense mass (open arrow) in the midline covering the foramina of Monro. The lateral ventricles (curved arrow) are enlarged. Axial T2WI MR (#2), T1WI MR (#3), T1 WI C+ MR (#4), and DWI MR (#5) show that the mass (open arrows) is of intermediate T2 (#2) and slightly high T1 (#3) signal intensity with no significant enhancement (#4). No restricted diffusion is seen in the mass (#5). Mild increased T2 signal intensity surrounds the frontal horns of the lateral ventricles (straight arrow, #2), typical of interstitial edema in the setting of obstructive hydrocephalus.', 'history': 'Headaches.', 'imagePoolId': '6440685f-5830-4007-ac86-a5a57beff7af', 'name': 'T1 bright, hydrocephalus', 'teachingPoint': 'This mass is a typical appearance for a colloid cyst with mild hydrocephalus.', 'demographics': '14 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'e0c3703a-3371-4f49-b7ec-0453197536f7', 'description': 'Classic colloid cyst shown on CT.\n\nAxial NECT shows a round hyperdense foramen of Monro mass (open arrow) causing mild hydrocephalus. Note fornices (arrows) are draped and splayed around the mass.', 'history': 'Sudden onset of headache, papilledema.', 'imagePoolId': '0dff071c-507f-434f-94ca-fec4547efa13', 'name': 'Hyperdense mass', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'c11df014-01dd-479f-8ae4-f1e3d084fdb7', 'description': 'Tiny colloid cysts can sometimes be detected on MR when they are viscous and therefore hyperintense on T1 weighted sequences.\n\nSagittal (#1) and coronal (#2) show a very small mildly hyperintense mass at the foramen of Monro (arrow). The lesion is isointense with gray matter on T2WI (#3, arrow). Sagittal (#4) and coronal (#5) post-contrast T1WIs demonstrate slight displacement of the choroid plexus and internal cerebral veins (arrows) by the mass.', 'history': 'Incidental finding.', 'imagePoolId': '268267df-ebfc-4701-ab3b-556aa596698f', 'name': 'Viscous', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'fbaeb781-1e71-40e2-a236-ee41ca33a472', 'description': 'Colloid cysts vary in signal intensity and can sometimes be mostly isointense with brain on MR.\n\nAxial T2WI MR (#1), shows a colloid cyst (arrow) at the foramen of Monro. The cyst is isointense with brain and is causing moderate but compensated hydrocephalus. The cyst remains isointense with brain on T2WI (#2, arrow). Axial FLAIR MR (#3), shows the cyst (arrow) does not suppress and is hyperintense to brain. Note absence of transependymal CSF flow around atria of lateral ventricle. The contrast-enhanced fat-suppressed T1WI (#4) shows the cyst does not enhance. Note deviation of the internal cerebral veins around the cyst (open arrows).', 'history': 'Middle-aged female with headaches.', 'imagePoolId': 'd088e38b-f110-43ba-8ec5-393853851476', 'name': 'Classic', 'teachingPoint': None, 'demographics': '42 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '4384758a-9ba0-4853-b927-4922454e7123', 'description': 'Close-up view of an NECT scan obtained in this case shows a focal hyperdense area at the foramen of Monro (arrow). This represents a hemorrhagic axonal stretch injury to the fornix, a compact white matter fiber tract that occasionally is involved by the sudden deceleration/rotational forces seen in closed head injury. In this case the DAI is right at the foramen of Monro. Without the history it might be mistaken for a colloid cyst with the fornices straddling the cyst.', 'history': 'Closed head injury.', 'imagePoolId': 'a28629e4-6e8d-4d36-a8a1-3b8e8383f668', 'name': 'Axonal injury to fornix mimics colloid cyst', 'teachingPoint': None, 'demographics': '16 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'ab653321-4742-4948-8880-be53cd110639', 'description': 'NECT scan shows a 3-mm nonobstructive hyperdense mass at the foramen of Monro (arrow, #1). Series of MR scans (#2-5) show the mass (arrows) is essentially isointense with brain on all sequences, rendering it essentially invisible on MR.', 'history': 'Young adult with headaches.', 'imagePoolId': '8bbfaea2-5a8c-4c4c-874a-074d51ad75b8', 'name': 'Invisible on MR', 'teachingPoint': "This may have been an incidental finding on this patient's NECT scan, given the size of the mass. However, occasionally colloid cysts, even small ones, can cause intermittent or acute obstruction at the foramen of Monro. They may be life-threatening in some cases. Had only an MR scan been obtained, this small colloid cyst could easily have been overlooked."}], 'caseType': 'typical', 'name': 'TYPICAL'}
{'cases': [{'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '14f4945b-54ff-4137-9543-460eb1a9114f', 'description': 'NECT scan (#1) shows well-delineated hyperdense mass at the foramen of Monro (arrow). No enhancement could be identified on CECT scan (#2). MR was obtained. Axial T1WI (#3) shows slightly hyperintense mass within the foramen of Monro (arrow). The lesion was very hypointense on sagittal and axial T2WIs (arrows, #4,5). The ventricles are moderately enlarged. Axial and coronal FLAIR scans (#6,7) show a mostly hypointense lesion with a distinct hyperintense rim (arrows). T1C+ scan (#8) shows rim enhancement around the lesion (arrow).\n\nThe lesion was removed. Histopathologic examination of the surgical specimen (#9) showed classic colloid cyst. Flattened cuboidal to low columnar epithelium with interspersed goblet cells and some flattened basal cells surrounded amorphous material that comprised the cyst contents. Scattered foci of chronic inflammatory infiltrates were identified.', 'history': 'Patient in ER with sudden-onset severe ("thunderclap') headache, nausea, vomiting. NECT scan was obtained to look for subarachnoid hemorrhage.', 'imagePoolId': '5f81d46e-69d1-4d27-b356-c14b406ac01f', 'name': 'Hypointense on T2; ring-enhancing', 'teachingPoint': 'A colloid cyst with densely inspissated cyst contents was found at surgery. Mild reactive inflammatory changes around the cyst periphery probably account for the rim enhancement seen on MR.', 'demographics': '65 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'f0954471-c873-4868-bc64-00a3952b3520', 'description': 'Axial T1Ws (#1, 2), show a classic hyperintense lesion at the foramen of Monro. The lesion is isointense with gray matter on T2WIs (#3, 4). Sagittal (#4) and axial (#5) T1WI MR images, were obtained when the patient developed a sudden increase in headaches. They show marked interval enlargement of the mass and worsening hydrocephalus. The mass appears rather inhomogeneous on T2WI (#6).', 'history': 'The patient initially presented with only mild headaches. Observation rather than surgical intervention was the chosen treatment. The patient subsequently, however, developed a sudden increase in headaches, correlating with the enlarging cyst.', 'imagePoolId': '4a886534-855f-4218-868e-f16a9872b809', 'name': 'Enlarging', 'teachingPoint': 'It is unusual for colloid cysts to show rapid change in size but it does occur.'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '342415d2-2b04-45d3-bf98-6eb243f733b6', 'description': 'NECT scan (#1) shows moderate enlargement of the lateral ventricles, with "blurring" of the ventricular margins. The posterior aspects of the frontal horns appear splayed laterally (arrows). Sagittal (#2) and axial (#3) T1WIs show the fornix draped superiorly and anteriorly around a mass at the foramen of Monro (arrows). The mass is approximately isointense with gray matter. Axial PD (#4), as well as axial (#5) and coronal (#6) T2WI show the mass is hyperintense. Note: focus of relative hypointensity (arrow, #6). Sagittal (#7) and axial (#8) FLAIR scans show the lesion does not suppress and remains hyperintense. Note transependymal CSF flow (arrows, #8). The lesion shows minimal rim enhancement on axial (#9) and coronal (#10) T1C+ scans (arrows).', 'history': 'Teenaged male presented in the ER with severe headaches. Papilledema was found on physical examination.', 'imagePoolId': '5f378739-c667-4774-b605-bbd0ffda3c67', 'name': 'Isodense', 'teachingPoint': 'The appearance is typical for a colloid cyst on MR. What is atypical about this case is its isodensity with brain on NECT scan as well as the relatively young age of the patient. Colloid cysts are less common in children and adolescents compared with adults.', 'demographics': '16 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '6e6df753-a53e-44ee-b833-81aede500ba1', 'description': 'Colloid cysts may be isodense with surrounding brain and difficult to detect on CT scans.\n\nAxial NECT scan (#1) shows focal deformity of the frontal horns, which appear splayed posteriorly at the foramen of Monro (arrows). No definite mass is identified.\n\nA series of MR images (#2-8) clearly show a mass at the foramen of Monro. Sagittal (#2) and axial (#3) T1 weighted scans show the mass is mostly iso- to slightly hyperintense with brain (arrows). Note the forniceal splaying (#4, arrows) and central hypointensity (#5, arrow) on T2 weighted scans. The cyst does not suppress on FLAIR and the central hypointense focus is clearly seen (#6-7). Slight rim-enhancement is identified on the post-contrast T1WI (#8, arrow). This may represent displaced choroid and internal cerebral and/or septal veins around the mass.', 'history': None, 'imagePoolId': '95a7ec82-d0ba-41c2-a393-2e172c99ced9', 'name': 'Isodense', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '53c375b9-8d72-4224-ad18-694faa4a84fe', 'description': 'Occasionally colloid cysts show rim-enhancement.\n\nAxial NECT scan shows moderately severe hydrocephalus with blurring of the ventricular margins caused by transependymal extravasation of CSF. There is some splaying of the posterior aspects of the frontal horns (#1, arrows) but if a mass is present (it is), its attenuation is identical to surrounding brain which renders it invisible. CECT scan (#2) shows faint rim-enhancement (arrows). Colloid cyst was removed at surgery.', 'history': 'Lethargic with decreased mental status.', 'imagePoolId': 'dc8e669e-abef-48e6-b49c-1bf34e73621a', 'name': 'Rim-enhancing', 'teachingPoint': None, 'demographics': '24 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '3cc37fe5-4346-462a-b9e9-c75f8644caad', 'description': 'Sagittal (#1) and axial (#2) pre-contrast T1-weighted scans show a well-delineated mass at the foramen of Monro (arrow). The mass is isointense with brain on both T1 and T2 weighted (arrows, #3, 4) sequences. The lesion is hyperintense on FLAIR (arrow, #5). Note: presence of striking subependymal CSF flow on this image (open arrows). T1C+ scans (#6-8) show the lesion enhances (arrows).\n\nColloid cysts do not show solid enhancement, as this case does. A few ring-enhancing colloid cysts have been described but are unusual.', 'history': 'Known renal carcinoma, severe headaches.', 'imagePoolId': 'bd38c230-2389-4569-bdac-b1fa9df3f52a', 'name': 'Met mimics colloid cyst', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'd5c2031b-f1de-49ac-b0bd-587fff55834a', 'description': 'The first slice in the coronal T1-weighted scan shows striking flow artifact within the third and lateral ventricles (arrows). If you look at the adjacent brain parenchyma, you see propagation of phase artifact (open arrows) across the scan indicating this is flow-related.', 'history': 'Headaches.', 'imagePoolId': '365f2a97-0918-4bcd-944c-9a72bb93b31d', 'name': 'CSF flow mimics colloid cyst', 'teachingPoint': None, 'demographics': '56 Years old female'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'db053f71-cf48-44e4-b6a7-5446af5e4bf0', 'description': 'Axial NECT scan (#1) obtained at an outside hospital shows a hyperdense mass near the foramen of Monro (arrow). Note markedly enlarged ventricles with "blurry" margins indicating transependymal CSF flow (open arrows). CECT scan (#2) shows the mass enhances strongly and uniformly (arrow). Initial diagnosis was colloid cyst. A shunt was placed in the lateral ventricles and the patient transferred for emergent "removal of colloid cyst."\n\nReview of the imaging study led to the revised diagnosis of extremely ectatic basilar artery that protruded into the third ventricle and caused obstructive hydrocephalus.\n\nColloid cysts do not enhance strongly and uniformly. In older patients, vertebrobasilar ectasia (VBD) can present as a mass indenting the third ventricle and even the foramen of Monro.', 'history': 'Older patient with severe headaches, papilledema on physical examination.', 'imagePoolId': '60ef074e-b74e-4018-8c8c-32f25ce28eab', 'name': 'VBD mimics colloid cyst', 'teachingPoint': None, 'demographics': '61 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'dbaeb2a6-3112-477b-8c76-88de5f51769c', 'description': 'Flow artifacts in and around the third ventricle and foramen of Monro can mimic colloid cyst. \n\nAxial FLAIR scans (#1, 2) show inhomogeneous signal within the third ventricle and foramen of Monro (arrows). Coronal T1C+ scans (#3, 4) show hyperintensity in the anterior third ventricle (arrows).\n\nNote that the intraventricular signal is in the inferior third ventricle, below the foramen of Monro, seen especially well on image 4. Colloid cysts are typically in the upper aspect of the third ventricle, wedged between the fornices (#4, curved arrow).', 'history': 'Headaches, no neurologic findings.', 'imagePoolId': '11afc5aa-126f-4b75-b839-eee61bbd9c61', 'name': 'Flow mimics colloid cyst', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'e04b071c-ee82-4768-b79b-cc8e39c3dc9b', 'description': 'Sagittal (#1) and axial (#2) T1WIs show an isointense 3rd ventricular mass (arrows). It appears hyperintense on PD (#3) and T2WI (#4). Note transependymal CSF flow (arrows,#3, 4). On T1C+ scan the mass showed striking rim enhancement (arrow, #5).', 'history': 'Headaches.', 'imagePoolId': '0c8825e0-a803-48fd-8d88-9fc54e86f776', 'name': 'Rim enhancement', 'teachingPoint': 'Rim enhancement around the margin of a colloid cyst is unusual. It may represent inflammatory reaction to the cyst or, in some cases, displacement of veins and choroid plexus around the cyst. In this case, some inflammatory changes were found surrounding the cyst that was surgically removed.'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': 'fbb1c89e-1071-4b58-a5f4-902c5f7eed30', 'description': 'Close-up views of the axial NECT (#1) and CECT scans (#2) show a hyperdense mass in the 3rd ventricle (arrows). The mass is somewhat oblong and seems to fill the third ventricle. This would be unusual for a colloid cyst and may represent a xanthogranuloma of the 3rd ventricular choroid plexus.', 'history': 'Patient presented at an outside emergency room with severe headache. Papilledema was found on physical examination. CT scan was obtained emergently but the patient collapsed and died. Autopsy was refused.', 'imagePoolId': 'aad4004a-ea21-4c77-b4ee-b68a15cca8ff', 'name': 'Xanthogranuloma mimics colloid cyst', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '0ad4295d-eb86-4a4e-8701-a7d9091e9c80', 'description': 'Single coronal T1WI shows a hyperintense mass within the inferior third ventricle. The mass is too low for a colloid cyst, which are typically wedged into the roof of the third ventricle just below the fornices. Intraventricular pituitary adenoma was found at surgery. Ectopic pituitary adenomas may occur in many locations, including the sphenoid sinus and third ventricle.', 'history': None, 'imagePoolId': '795a57d3-76f5-42bb-a75f-c5574664410b', 'name': 'Ectopic pituitary adenoma mimics colloid cyst', 'teachingPoint': None}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '0fe2ba0f-4902-4e98-859d-a21a034c7554', 'description': 'Axial NECT scan (#1) shows a slightly hyperdense mass at the foramen of Monro (arrow). The mass enhances very strongly on CECT (arrow, #2). Initial diagnosis was colloid cyst.\n\nAfter transfer to the University Hospital, an MR scan was obtained. The axial T1WI (#1) shows the "colloid cyst" is vascular with high flow (arrow) causing phase artifact to propagate across the image (open arrows). This was caused by extreme fusiform ectasia of the basilar artery.', 'history': 'Elderly patient with headaches had a CT scan performed at an outside clinic.', 'imagePoolId': 'dd5fccfc-bcf8-45ad-977d-28af4a53a7f2', 'name': 'VBD mimics colloid cyst', 'teachingPoint': None, 'demographics': '73 Years old male'}, {'authors': [{'key': '5cff4116-3654-4b3a-bb75-5ebe0b8c9850', 'value': 'Anne G. Osborn, MD, FACR'}], 'caseVersionId': '70c8836e-137d-4411-a718-b1e9af2ba0ef', 'description': 'Axial T1WI MRs (#1-2), show a large, lobulated foramen of Monro mass. Axial T2WI MRs (#3-4), show a mixed signal mass with a focus of profound hypointensity ("black hole" effect), indicated by the arrow.', 'history': 'Middle-aged patient with headache and obstructive hydrocephalus. An unusually large, very viscous colloid cyst was found at surgery.', 'imagePoolId': '6ca864d5-f385-42e7-9567-195c94b07fb0', 'name': '"Black hole" effect', 'teachingPoint': 'The signal intensity of colloid cysts varies widely. If the proteinaceous contents become very desiccated and inspissated, the cyst can appear rather unusual, as is illustrated by this case.'}], 'caseType': 'variant', 'name': 'VARIANT'}

Images

Selected Images

Axial graphic shows a classic colloid cyst (CC) 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 CC causing moderate obstructive hydrocephalus. A small cavum septi pellucidi is present. Fornices are draped over the cyst. (Courtesy R. Hewlett, MD.)

Axial NECT obtained to look for a subarachnoid hemorrhage in a 65-year-old man with a thunderclap headache shows a classic CC, 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 CC was removed emergently.

Axial T1WI MR in a 52-year-old man with headache, amnesia, and TIA-like symptoms shows a large, mildly hyperintense, well-delineated mass in the 3rd ventricle and foramen of Monro. Note the blood-fluid level in the dependent part of the mass.

Axial T2WI MR in the same patient shows the mass is cystic and even more hyperintense than cerebrospinal fluid (CSF) in the adjacent ventricles. Note the blood-fluid level and splaying of the fornices around the mass.

Axial thin-section T2-space MR shows the fornices draped around the mass.

Axial FLAIR MR shows the cyst is extremely hyperintense and does not suppress. Note hyperintensity in the fornices and adjacent corpus callosum genu , suggesting edema from acute inflammation.

Axial T1 C+FS MR shows rim enhancement around the cyst wall.

Coronal T1 C+ MR in the same patient shows the rim enhancement surrounds the entire cyst wall. Diagnosis of a CC with apoplexy, intracystic hemorrhage, and inflammatory changes was documented at surgery.

Additional Images

Axial NECT in a 16-year-old boy who presented in the ER with severe headaches and papilledema shows severe obstructive hydrocephalus with dilated lateral ventricles and complete effacement of all superficial sulci. An isodense mass is present at the foramen of Monro.

Axial FLAIR MR in the same patient shows the lesion to be very hyperintense and straddled by the fornix . Ventricles are dilated and transependymal CSF flow is present. The CC was removed at surgery.

Axial T1WI MR shows a slightly hypointense CC . Note the pillars of fornix elevated and draped over cyst.

Axial NECT shows a round, hyperdense foramen of Monro mass causing mild hydrocephalus. Note the fornices draped and splayed around the mass. This is a classic CC.

Axial T2WI MR shows a CC at the foramen of Monro. The cyst is isointense with the brain and is causing moderate, but compensated, hydrocephalus.

Axial FLAIR MR in the same patient shows that the cyst does not suppress and is hyperintense to brain. Note the absence of transependymal CSF flow around the atria of the lateral ventricle.

Axial T1WI MR shows a large, lobulated foramen of Monro mass in a middle-aged patient with headache and obstructive hydrocephalus.

Axial T2WI MR in the same case shows a mixed signal mass with a focus of profound hypointensity ("black hole" effect) . An unusually large, inspissated viscous colloid cyst was found at surgery.

Axial T1WI MR shows a classic CC at the foramen of Monro. This patient had only mild headaches. Observation rather than surgical intervention was the chosen treatment.

Axial T1WI MR in the same patient, obtained after the patient developed a sudden increase in headaches, shows marked interval enlargement of the mass. The CC now appears less hyperintense and hydrocephalus is present. The CC was removed at surgery.

Sagittal T1WI MR shows a tiny CC discovered incidentally in this asymptomatic patient.

Axial NECT in a 24-year-old man with severe headaches shows a hyperdense mass at the foramen of Monro. The superficial sulci are effaced and the brain appears "tight", suggesting moderate cerebral edema.

Axial T1WI MR in the same patient shows the mass is slightly hyperintense compared to the brain.

Axial T2WI MR in the same patient shows most of the cyst appears relatively isointense with gray matter, but exhibits a central hypointense focus that suggests inspissated colloid within the cyst.

Coronal T2WI MR shows the central inspissated cyst as very hypointense. Note elevation and splaying of the fornices around the cyst.

Axial T1 C+ SPGR MR for stereotaxic surgery shows enhancement around the lateral margins of the cyst. This represents displaced internal cerebral and septal veins, not rim enhancement. An inspissated CC was removed at surgery.

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KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

Diagnostic Checklist

TERMINOLOGY

Abbreviations

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

Morphology

CT Findings

NECT

CECT

MR Findings

T1WI

T2WI

FLAIR

DWI

T1WI C+

MRS

Imaging Recommendations

Protocol advice

DIFFERENTIAL DIAGNOSIS

Cerebrospinal Fluid Flow Artifact (MR "Pseudocyst")

Neoplasm

Choroid Plexus Mass

PATHOLOGY

General Features

Etiology

Genetics

Associated abnormalities

Gross Pathologic & Surgical Features

Microscopic Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Clinical profile

Demographics

Age

Sex

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

References

Selected References

Cases

Images

Selected Images

Additional Images

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