Colloid Cyst (Transcallosal Approach)
Last Updated: September 29, 2018
Colloid Cysts represent 0.5-1% of intracranial lesions and are located within the third ventricular roof immediately adjacent to the foramen of Monro. These cysts uniquely contain a viscous gelatinous material and originate from abnormal folding of the primitive neuroepithelium (the paraphysis elements).
Colloid cysts can reach a substantial size and exceedingly rarely precipitate a sudden occlusion of the foramen of Monro, causing life-threatening acute obstructive hydrocephalus. The method of occlusion can be related to acute intracystic hemorrhage, postlumbar puncture transposition of the mass, or shunt malfunction.
In most cases, colloid cysts are asymptomatic and discovered incidentally.
Diagnosis and Evaluation
For a general discussion of diagnosis and evaluation for ventricular tumors, including colloid cysts, see the Principles of Intraventricular Surgery chapter.
Colloid cysts appear as mildly hyperdense lesions on computed tomography (CT) scan and may rarely contain calcifications. On T2-weighted sequences, they are hyperintense compared to white matter; on T1 images, they lack contrast enhancement. These lesions do not generally increase significantly in size; however, intracystic hemorrhage can lead to giant cysts.
Radiographic differential diagnosis for a colloid cyst includes a cystic craniopharyngioma, a posterior circulation aneurysm, neurocysticercosis, and vertebrobasilar dolichoectasia.
Indications for Surgery
Management of colloid cysts depends upon the patient’s clinical state. Asymptomatic lesions may be managed conservatively with routine radiographic evaluation for interval change. If the patient becomes symptomatic, endoscopic or microsurgical resection is appropriate
Resection of asymptomatic lesions is a matter of intense controversy because acute life-threatening hydrocephalus is possible, although exceedingly rare. Large cysts (>10mm in diameter) have been noted to be potentially associated with an increased risk of causing hydrocephalus. Overall, there is no reliable indicator for a need to intervene among asymptomatic lesions that are not associated with hydrocephalus; I do recommend observation for these patients.
Headaches, in the absence of hydrocephalus, is not an indication for intervention.
Patients suffering from symptomatic acute hydrocephalus require emergent ventriculostomy. I usually plan to approach the lesion via the nondominant interhemispheric corridor unless the dominant ventricle is substantially larger on preoperative imaging.
I prefer the use the transcortical transtubular corridor for patients with significant hydrocephalus because intercingulate dissection via the transcallosal route can place both cingula at risk. However, mild to moderate hydrocephalus may not provide enough working space within the frontal horn; the transcallosal route is suitable in these instances.
I have not used the endoscopic method for resection of colloid cysts because it is difficult to consistently achieve gross total cyst wall removal with this method. A risk of future cyst recurrence persists. Nonetheless, endoscopic resection is reasonable for older patients with symptomatic cysts.
Please refer to the Anatomy of the Ventricular System for further details.
MICROSURGICAL TRANSCALLOSAL RESECTION OF COLLOID CYSTS
The transcallosal approach is ideal for patients suffering from mild hydrocephalus.
Please refer to the Interhemispheric Craniotomy and Lateral Ventricular Tumors chapters for further details related to craniotomy and exposure of the lateral ventricle. Intraoperative navigation is important for selection of a precise operative trajectory and a minimal callosotomy.
Transcallosal approaches are ideal for strictly midline lesions without significant lateral expansion.
The surgeon should avoid injuring the genu of the internal capsule, located lateral to the foramen of Monro and separated by a thin layer of ventricular capsule where the thalamostriate vein orients medially to anastomose with the internal cerebral vein.
The ventricular cavities are generously irrigated to evacuate any debris and control minor bleeding. I do not leave a ventricular catheter in place after resection of colloid cysts. This procedure is usually pristine. However, if the patient required preoperative placement of an external ventricular drain, the drain is left in the ventricle and weaned off postoperatively.
For a detailed discussion of postoperative care of patients with ventricular tumors, see the Principles of Intraventricular Surgery chapter.
Pearls and Pitfalls
- Early decompression of the cyst and gentle handling of the fornix and ventricular walls secure optimal outcomes. The cyst should not be pulled out before its thorough circumdissection.
Contributor: Benjamin K. Hendricks, MD
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