Brain Imaging in Colloid Cyst 

Updated: Aug 28, 2018
  • Author: Andrew L Wagner, MD; Chief Editor: L Gill Naul, MD  more...
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Practice Essentials

Colloid cysts are benign, congenital epithelium-lined cysts that most commonly occur in the third ventricle near the Monro foramen. Extraventricular locations are very rare but have been reported in the cerebellum, olfactory groove, optic chiasm, cerebral hemisphere, fourth ventricle, brainstem, pituitary gland, and velum interpositum. [1] The cysts are believed to derive from either primitive neuroepithelium of the tela choroidea or from endoderm. [2]  

Colloid cysts account for approximately 1% of all intracranial tumors and are the most common type of the neuroepithelial cysts, as well as the most common tumor in the third ventricle. Typically, patients are asymptomatic; however, if the tumor obstructs the foramen of Monro, hydrocephalus, rapid clinical deterioration, and death may occur.​ [3] The diagnosis is usually made by assessing the typical location and appearance of the cyst. 

(See the images of colloid cysts below).

Sagittal nonenhanced T1-weighted magnetic resonanc Sagittal nonenhanced T1-weighted magnetic resonance image. This image demonstrates a round area of increased signal intensity in the anterosuperior portion of the third ventricle (arrow).
Axial fluid-attenuated inversion recovery magnetic Axial fluid-attenuated inversion recovery magnetic resonance image. This image shows a bright mass.
Axial contrast-enhanced T1-weighted magnetic reson Axial contrast-enhanced T1-weighted magnetic resonance image. This image demonstrates a small amount of peripheral enhancement but no discernible central enhancement. Note the location of the colloid cyst near the foramina of Monro.
Computed tomography scan in a 65-year-old man who Computed tomography scan in a 65-year-old man who had acute onset of headache. This image demonstrates a round area of increased attenuation at the foramina of Monro, with hydrocephalus. The image is degraded because of motion artifact, as the patient was in severe pain at the time of imaging.
Axial computed tomography scan in a 50-year-old ma Axial computed tomography scan in a 50-year-old man who was transported to the emergency department after falling down while lifting weights; he later had cardiopulmonary arrest. This image demonstrates a hyperattenuating colloid cyst at the foramina of Monro, with marked hydrocephalus.

Patients with colloid cysts of the third ventricle who experience rapid deterioration and death tend to be younger, have long-standing symptoms, and have cysts at least 8 mm in diameter.  As a result, asymptomatic patients with lesions less than 7 mm have historically undergone observation with serial imaging, while those with larger lesions have undergone cyst resection or CSF shunting. [4]   

As the use of neuroimaging becomes more commonplace, colloid cysts are being increasingly identified incidentally. One review of 176 patients with asymptomatic colloid cysts who received radiologic follow-up reported 86.7% of cysts remained stable (95% CI, 78.5-92.2), 11.2% progressed (95% CI, 6.2-19.2) and 2.0% regressed in size (95% CI, 0.1-7.6). [3]  

Shapiro et al described the long-term results of an interhemispheric, transcallosal, subchoroidal, fornix-sparing approach to gross-total resection of colloid cysts. In 57 colloid cysts, total removal was achieved via a 3 x 3-in paramedian craniotomy flap and a microscopic interhemispheric, transcallosal, subchoroidal approach sparing the ipsilateral fornix. According to the investigators, at 1 year after surgery, computed tomography (CT) scanning or magnetic resonance imaging (MRI) confirmed gross-total resection, with no infection, hemiparesis, seizures, or disconnection syndrome. There were no deaths or recurrences. The authors noted that the results were superior to those seen with endoscopy. [5]

Preferred examination

Either CT scanning or MRI may help diagnose a colloid cyst, although MRI has a few advantages. [6, 7] The multiplanar capabilities of MRI optimally demonstrate the location of the cyst, and typical signal intensities in the cyst help confirm the diagnosis, but CT scanning is usually adequate for the diagnosis of a colloid cyst. T2-weighted MRI sequences may be useful to assess the nature of the intracystic contents and to predict the difficulty of aspiration during endoscopic or stereotactic procedures. [8, 9, 10, 11, 12]

Typically, colloid cysts are clinically silent and are found incidentally when patients are imaged for other reasons. When patients are symptomatic, they typically experience chronic headaches, which may be intermittent and positional because of transient CSF obstruction. On rare occasions, a colloid cyst may completely and irreversibly obstruct the foramen of Monro, resulting in sudden loss of consciousness and, if patients are not treated, in coma and death. [13]

Pollock et al reviewed 155 cases of colloid cyst and found 4 factors that were associated with colloid cyst–related clinical symptoms [14] : (1) younger patient age, (2) increased cyst size (average of 13 mm in symptomatic patients vs 8 mm in asymptomatic patients), (3) ventricular dilatation (although 31% of asymptomatic patients had this finding), and (4) increased signal intensity on T2-weighted MRIs. These findings suggest that slowly growing colloid cysts may allow for compensation by the brain, thus avoiding symptoms. In addition, findings of high T2 signals in symptomatic patients suggest that the more-serous colloid cysts enlarge the fastest.

The appearance of colloid cysts on CT and MRI scans is important in planning treatment, because the success rate after percutaneous aspiration is lower in colloid cysts that have high attenuation on CT scans and decreased MRI T2-signal intensity than in the cysts that have fluid characteristics. [15] Interestingly, the cysts with high T2-signal intensity are easier to treat with minimally invasive surgical techniques; however, these cysts are also the ones that are most likely to cause clinical symptoms.

Intraventricular hemorrhage occasionally mimics a colloid cyst on CT scans and MRI. Subependymomas, central neurocytomas, and subependymal astrocytomas may occur in the same area as a colloid cyst on imaging studies, but these entities can be distinguished by their shape, contrast enhancement, and signal intensity.

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Computed Tomography

CT scan findings include a round mass with high attenuation at the anterior third ventricle. Rarely, colloid cysts may be isoattenuating or hypoattenuating relative to brain parenchyma. The typical high attenuation likely results from proteinaceous fluid.

Hydrocephalus, which can be severe, results when the cyst obstructs the lateral ventricles at the foramen of Monro. This finding can be intermittent, as the cyst can act as a ball valve. Patients may then present with intermittent positional headaches.

A nonenhancing area of high attenuation in the typical location is almost diagnostic of a colloid cyst, but most clinicians confirm the diagnosis with MRI.

(See the images below.)

Computed tomography scan in a 65-year-old man who Computed tomography scan in a 65-year-old man who had acute onset of headache. This image demonstrates a round area of increased attenuation at the foramina of Monro, with hydrocephalus. The image is degraded because of motion artifact, as the patient was in severe pain at the time of imaging.
Axial computed tomography scan in a 50-year-old ma Axial computed tomography scan in a 50-year-old man who was transported to the emergency department after falling down while lifting weights; he later had cardiopulmonary arrest. This image demonstrates a hyperattenuating colloid cyst at the foramina of Monro, with marked hydrocephalus.

 

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Magnetic Resonance Imaging

Colloid cysts are well demonstrated on MRI scans and are found near the foramen of Monro, just posterior to the fornices in the anterosuperior third ventricle. The MRI findings depend on the composition of the cyst content, that is, cerebrospinal fluid–like or mucous cyst content. Approximately half of the cysts are hyperintense on T1-weighted images, whereas T2-weighted images are variable. Colloid cysts do not show enhancement even in the cyst wall. [12]  Rarely, inspissated debris may form a dependent nodule that can be seen on CT and MRI scans.

The diagnosis of a colloid cyst is made based on the classic location, appearance, and signal intensity. Central contrast enhancement suggests an alternative diagnosis, but most other pathologies that occur in this location are easily distinguishable from colloid cysts. Colloid cysts do not have intrinsic enhancement; the presence of enhancement suggests a solid tumor. Peripheral enhancement may be present because of vascularity in the outer wall. [16]

El Khoury et al found that low signal intensity of colloid cysts on T2-weighted images corresponded to difficult percutaneous aspiration in 100% of cases, whereas most of the cysts with high T2-signal intensity were considered easy to aspirate. [17]

(See the images below.)

Sagittal nonenhanced T1-weighted magnetic resonanc Sagittal nonenhanced T1-weighted magnetic resonance image. This image demonstrates a round area of increased signal intensity in the anterosuperior portion of the third ventricle (arrow).
Axial fluid-attenuated inversion recovery magnetic Axial fluid-attenuated inversion recovery magnetic resonance image. This image shows a bright mass.
Axial contrast-enhanced T1-weighted magnetic reson Axial contrast-enhanced T1-weighted magnetic resonance image. This image demonstrates a small amount of peripheral enhancement but no discernible central enhancement. Note the location of the colloid cyst near the foramina of Monro.

 

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