Colloid Cysts 

In 1858, Wallmann first reported on colloid cysts. In 1921, Dandy accomplished the first successful resection of a colloid cyst.

Colloid cysts are benign congenital tumors that almost always arise from the anterior third ventricle (immediately posterior to the foramen of Monro). These epithelium-lined cysts are problematic because of their location; colloid cysts can cause serious morbidity and occasional mortality that may lead to acute obstructive hydrocephalus, increased intracranial pressure, and, rarely, intracystic hemorrhage.

The image below depicts a colloid cyst.

Frequency

Although these tumors are considered congenital, their presentation in childhood is rare (the youngest reported case involved a 2-month-old infant). The tumors are usually symptomatic in patients aged 20-50 years. Approximately 0.5-1% of all primary brain tumors and 15-20% of all intraventricular masses (most common) are colloid cysts. No known genetic relationship has been determined, although familial occurrences of colloid cysts have been reported. With the advent of CT scanning and MRI, the number of diagnosed asymptomatic colloid cysts has increased.

The etiology of this tumor is still a source of debate. In 1910, Sjovall hypothesized that colloid cysts were remnants of the paraphysis, an embryonic midline structure within the diencephalic roof immediately rostral to the telencephalic border. The cells of the paraphysis are similar to those found in colloid cysts, (ie, low columnar epithelial cells without cilia or blepharoplasts). These cysts were called paraphysial cysts for 50 years; however, several reports have been written about colloid cysts found in other locations, including the posterior third ventricle, the fourth ventricle, and the septum. Rare locations in the frontal lobe,^[1] cerebellum, and pontomesencephalon have also been described. The origin of these cysts continues to be uncertain. Diencephalic ependyma, invagination of neuroepithelium of the ventricle, or the respiratory epithelium of endodermal origin are other etiologic possibilities.

Colloid cysts enlarge by increased secretion of mucinous fluid from their epithelial cell wall lining. In addition, cyst cavities may be filled with blood degradation products such as cholesterol crystals.

Typically, colloid cysts are found incidentally. If symptomatic, colloid cysts are associated with the classic symptoms of intermittent obstructive hydrocephalus and paroxysmal headache associated with changing head position. In reality, the presentation is typically less specific. Headache may be part of the presentation, as well as vertigo, decreased memory, and behavioral changes. In addition, sudden weakness in the lower limbs associated with falls without loss of consciousness has been reported. Other symptoms are associated with signs of increased intracranial pressure (eg, papilledema, emesis). Additionally, symptoms similar to normal pressure hydrocephalus (eg, dementia, gait disturbance, urinary incontinence) have been associated with the presentation of colloid cysts.

In a study of 155 patients with newly diagnosed colloid cysts, Pollock et al described the following 4 factors associated with cyst-related symptoms:^[2]

• Younger patient age (44 y vs 57 y)
• Cyst size (13 mm vs 8 mm)
• Ventricular dilation (83% vs 31%)
• Increased signal on T2-weighted MRI (44% vs 8%).

The most significant variable of these was ventriculomegaly. For patients with enlarged ventricles, patient age (≤50 y vs >50 y) was the most important variable because patients aged 50 years or younger with enlarged ventricles were not affected by cyst size.

On rare occasions, a colloid cyst may obstruct the foramen of Monro completely and irreversibly, resulting in sudden loss of consciousness and, if patients are not treated, coma and subsequent death due to herniation. This theory of death secondary to herniation has recently been challenged with an alternative theory that suggests that sudden death in patients with colloid cysts may be related to acute neurogenic cardiac dysfunction (secondary to the acute hydrocephalus) and subsequent cardiac arrest rather than herniation.

The most common indication for surgery is hydrocephalus associated with a colloid cyst. This usually occurs in the setting of a large cyst that obstructs the foramen of Monro. A more difficult clinical setting occurs when patients present with few or no symptoms and have small colloid cysts and large ventricles. In many cases, these patients may be managed conservatively and observed with serial MRIs. Lastly, patients may have small cysts and normal-sized ventricles. These patients are not likely to deteriorate and do not need surgery.

Sudden death associated with colloid cysts has been reported, and the risk of sudden death may not correlate to tumor size, degree of ventricular dilatation, or duration of symptoms. Fortunately, the incidence of sudden death appears to be low; therefore, prevention of sudden death should not be used as an indication for surgery in asymptomatic patients with small cysts and no hydrocephalus.

Colloid cysts usually arise in the anterior portion of the third ventricle between the fornices. The cysts are attached to the roof of the third ventricle and frequently to the choroid plexus. Usually, the cysts are immediately dorsal to the foramen of Monro. These cysts have also been reported to frequently arise in the septum pellucidum, the fourth ventricle, and the sella turcica.

If patients are too ill to tolerate surgical resection, then cerebrospinal fluid (CSF) diversion, often requiring bilateral shunts, may be considered. This situation is suboptimal because sudden death has been reported in the absence of acute obstructive hydrocephalus.