Colloid Cysts
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Colloid Cysts

occur infrequently and account for less than 1 percent of intracranial tumors. However, there is a suggestion of an increased rate of detection coincident with improved neuroimaging techniques. They can produce symptomatic obstruction of the foramina of Monro and have been implicated as a cause of sudden deterioration and death, although their natural history is not well understood. They also may occur without causing symptoms and may appear as incidental findings at autopsy.

Colloid cysts are round or oval and vary in size from a few millimetres to several centimetres in diameter. The site of origin is most commonly the roof of the third ventricle at the level of the foramina of Monro. Such cysts are usually homogeneous and hyperdense on non contrast CT and show minimal enhancement after contrast administration. MRI shows similar characteristics (Fig.1). Small colloid cysts may be found incidentally; if this is the case and they are not causing problems, the patient should be followed carefully because the cysts can and do grow. Patients with symptomatic colloid cysts have two common clinical presentations. In the younger group, less than 40 years of age, the usual problem is unlocalized increased intracranial pressure in association with moderate hydrocephalus. A story of intermittent obstruction of the foramina of Monro causing headaches which are relieved by changes in head position seems to be overemphasized.

Likewise the incidence of sudden death due to an abrupt and complete blockage of CSF flow by these cysts is overstated. The cysts are not adherent to the foramen of Monro, are not very mobile, and rarely completely occlude the foramen. In most cases of sudden death there is a history suggestive of increasing intracranial pressure for weeks to months. Complete occlusion is obviously not necessary to interfere with CSF flow enough to cause hydrocephalus. In older patients, dementia and hydrocephalus without increased intracranial pressure can be seen.

The optimal surgical management of colloid cysts remains controversial. Surgical strategies, include a transcortical transventricular approach through a craniotomy, a transcallosal approach via a craniotomy, and a stereotactic craniotomy approach. Needle aspiration of the cyst contents has been proposed as an alternative to craniotomy. The various techniques for evacuating cyst contents include freehand aspiration, stereotactic aspiration, CT -assisted stereotactic aspiration and endoscopic aspiration. Shunting of one or both lateral ventricles may be useful in certain instances, but is considered to be the least satisfactory of all methods for dealing with colloid cysts.

Problems associated with cyst aspiration include difficulty penetrating a thick cyst wall, difficulty aspirating viscous cyst contents, and the possibility of neural or vascular injury if the procedure is not visualized by the surgeon. Failure of stereotactic cyst aspiration has been correlated with a hyperdense appearance on the preoperative CT scan. Recently, a high recurrence rate has been reported following aspiration of colloid cysts.

A rigid endoscope and its sheath are introduced into the lateral ventricle through a coronal burr hole, The colloid cyst is identified at the foramen of Monro and the cyst capsule is opened using a fiberoptic Nd:YAG laser introduced through a working channel in the endoscope sheath. Frequently small vessels are seen draped over the tumor capsule and these can be cauterized with the laser prior to opening the cyst. The cyst contents are then emptied with a suction catheter introduced through a working channel in the endoscope sheath. If the cyst contains solid material, this can be removed using grasping forceps, Once the cyst is emptied, the remaining capsule is coagulated and shrunk with the laser and then removed in a piecemeal fashion using microscissors and grasping forceps, The septum pellucidum can be fenestrated using the laser. The ventricular system is irrigated copiously and a ventricular drain is left in place for 48 h in an attempt to clear the irritative cyst contents. In addition, dexamethasone is administered perioperatively.

The ventriculoscope is useful in treating colloid cysts because it allows the operator several options. If after inspection the surgeon thinks that the cyst cannot be removed endoscopically, then either the cyst may be removed via a craniotomy or the septum may be fenestrated endoscopically and a ventricular shunt inserted, In medically unstable patients, endoscopic cyst evacuation may be performed under local anaesthesia.

Both groups of patients respond well to treatment of the hydrocephalus which is best accomplished by removing the colloid cyst. This can be done in a variety of ways, but it seems that the endoscopic approach may evolve as the least invasive and most beneficial way. In cases in which cyst removal is not a reasonable option for whatever reason, the hydrocephalus can be treated with a shunt. Each lateral ventricle may require shunting individually; however, this has not commonly been required because there is usually a defect in the septum pellucidum.



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