Colloid Cysts

History of the Procedure

In 1858, Wallmann first reported on colloid cysts. In 1921, Dandy accomplished the first successful resection of a colloid cyst through a transcortical transventricular approach. Since then, different operative approaches such as transcortical-transventricular and transcallosal were developed. [12345678910Less invasive techniques were then developed as an alternative to reduce the complications of the open approach. Freehand aspiration of a colloid cyst was performed first by Gutierrez-Lara et al in 1975. [11The first stereotactic aspiration of a colloid cyst was performed in 1978 by Bosch et al. [12Endoscopic aspiration of a colloid cyst was reported by Powell et al in 1983 [13and has progressively gained consensus as a safe alternative treatment.


Colloid cysts are non-neoplastic epithelium-lined cysts of the central nervous system that almost always arise from the anterior third ventricle roof (immediately posterior to the foramen of Monro). These epithelium-lined, mucin-containing cysts can be found in asymptomatic patients; however, depending on their location, size, and degree of cerebrospinal fluid (CSF) obstruction, patients may present with a variety of neurological symptoms. These symptoms can range from headaches to death on rare occasions when there is acute hydrocephalus. [14]

In a single-center retrospective review of 163 colloid cysts of the third ventricle according to Beaumont et al, about 60% of colloid cysts of the third ventricle were discovered incidentally during evaluation for other neurologic diseases, such as head trauma, stroke metastatic workup, and metabolic diseases. Five patients with incidental cysts (8.8%) progressed and underwent resection. However, none of the asymptomatic patients with incidental colloid cysts developed acute obstructive hydrocephalus or acute neurologic deterioration. Nearly half (46.2%) of symptomatic patients presented with hydrocephalus. Eight patients (12.3%) presented acutely, and there were 2 deaths due to obstructive,hydrocephalus and herniation. [14]

The image below depicts a colloid cyst at the foramen of Monro causing hydrocephalus.

Axial CT scan that shows a colloid cyst with assocAxial CT scan that shows a colloid cyst with associated hydrocephalus.


Colloid cysts account for approximately 2% of primary brain tumors, and the majority of cases are identified in the fourth and fifth decade. Eighty percent of the patients with colloid cyst reported in the literature are aged 30-60 years. Approximately 15-20% of all intraventricular masses are colloid cysts. Colloid cysts develop in the rostral aspect of the third ventricle in the foramen of Monro in 99% of cases, and despite their benign histology, they may carry high risks and neurologic complications, with a mortality reported from  3.1% to 10%  in symptomatic cases or 1.2% in total. [1415 

Although these tumors are considered congenital, their presentation in childhood is rare (the youngest reported case involved a 2-month-old infant).  The increased use of CT and MRI has resulted in an increased number of patients being diagnosed. No known genetic relationship has been determined, although familial occurrences of colloid cysts have been reported.


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, [16cerebellum, 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.


One leading theory is that colloid cysts form when ectopic endodermal elements migrate into the velum interpositum during central nervous system embryonic development. The fact that they are rarely seen in children indicates that they must enlarge with time. The cyst wall is lined with a mixed array of epithelial and goblet cells secreting proteinaceous mucinous fluid and may be responsible for the increase in size of the cyst. In addition, cyst cavities may be filled with blood degradation products such as cholesterol crystals.


Colloid cysts are often found incidentally, but when symptomatic, they present with obstructive hydrocephalus and paroxysmal headaches. These headaches are typically worse in the morning and may be exacerbated by leaning the head forward. Other symptoms are gait disturbances, short-term memory loss, nausea, vomiting, and behavioral changes. [15Sudden weakness in the lower limbs associated with falls and without loss of consciousness (drop attacks) have been reported. 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 [17:

  • Younger patient age (44 y vs 57 y)

  • Cyst size (13 mm vs 8 mm)

  • Ventricular dilation (83% vs 31%)

  • Increased cyst 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. An alternative theory 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 risk of sudden death remains difficult to predict. The presence of symptoms may be usefu,l as one study found that 8% of asymptomatic patients with a colloid cyst of the third ventricle eventually became symptomatic, [17whereas a different study found 34% of symptomatic patients presented to a hospital with acute deterioration and in some cases sudden death. [18]

Cyst size and extent of ventricular dilatation do not seem to predict for acute deterioration. [19In a study of 163 patients diagnosed with a colloid cyst of the third ventricle, Beaumont et al demontrated a strong correlation between the diameter of the cyst and the obstructive hydrocephalus. A similar correlation was also demostrated in this study between the hypersignal on FLAIR images of the cyst and the obstructive hydrocephalus. [14]


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 situation 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, but they should be counseled about the potential symptoms of hydrocephalus. Lastly, patients who have small cysts and normal-sized ventricles are not likely to deteriorate and do not need surgery.

Sudden death associated with colloid cysts has been reported, but the risk of sudden death does not seem to correlate with 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.

Relevant Anatomy

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.

Laboratory Studies

Routine preoperative studies, including a CBC count, chemistry panel, and coagulation studies are performed in addition to various imaging modalities.

Imaging Studies

CT scan

Colloid cysts appear homogeneous, with two thirds of them appearing hyperdense to the surrounding parenchyma and one third appearing isodense to the surrounding parenchyma. The lesions are well delineated and are usually round or ovoid. Occasionally, the lesions have a thin rim of enhancement after contrast injection, but they are typically nonenhancing and are not calcified. The size of these cysts varies, but most are 5-25 mm. [20]

Axial CT scan that shows a colloid cyst with assocAxial CT scan that shows a colloid cyst with associated hydrocephalus.

The CT scan is an important preoperative study because the viscosity of the cyst contents correlates more closely to the radiodensity visible on a CT scan than to the density visible on MRI. The viscosity of cyst contents determines the most appropriate surgical approach. A hyperdense cyst is more likely to have solid contents and is more difficult to drain. Hyperdensity may also correlate with a reduced capacity to enlarge over time.


The appearances of colloid cysts on MRIs are variable. The most common appearance is hyperintensity on T1 and hypointensity on T2. The amount of rim enhancement is variable. The variable MRI signals do not correlate with the fluid density of cyst contents, although a MRI is valuable in differentiating a colloid cyst from a basilar tip aneurysm, which may a have similar appearance on a CT scan. [2122232023]

Additionally, recognizing that a CSF flow artifact at the Monro foramen can mimic the appearance of a colloid cyst through MRI is important. Finally, the Constructive Interference in the Steady State (CISS) sequence of a MRI can delineate an abnormal contour of the ventricular system and intraventricular septa, from which essential information for surgical planning, including endoscopic surgery can be obtained. Postoperative CISS images can also be used, demonstrating not only regression of hydrocephalus but also the patency of small fenestrations.

In a retrospective study of 19 patients who underwent endoscopic management of colloid cysts of the third ventricle, El-Khoury et al found that 100% of lesions with low signal intensity on T2-weighted images had a higher intracystic viscosity contents that translated to an increased difficulty in aspiration of the contents. [24In contrast, 63% of patients with high-signal lesions were easy to aspirate. This differentiation may be useful in preoperative planning and management.

A retrospective study of 25 patients who underwent colloid cyst excision found specific MRI features suggestive of difficult cyst excision. In a subgroup of patients with preoperative hydrocephalus and imaging features suggestive of difficult removal, significantly higher rates of shunting were observed. The authors suggest using an open approach in cases of low T2, high T1 signal cysts with a diameter of over 15 mm, or CSF shunting in poor surgical candidates. For smaller cysts with a low T1 signal, a high T2 signal, and preoperative hydrocephalus, the authors recommend endoscopic intervention as the procedure of choice. [23]

Coronal MRI shows a colloid cyst in the roof of thCoronal MRI shows a colloid cyst in the roof of the third ventricle. The patient has mild hydrocephalus.
Intraoperative photograph through the operating miIntraoperative photograph through the operating microscope shows a colloid cyst in the Monro foramen. Choroid plexus is observed overlying the cyst, and the thalamostriate vein is along the inferior border.
Intraoperative photograph that shows removal of thIntraoperative photograph that shows removal of the cyst, leaving a dilated Monro foramen. The third ventricle can be seen through the opening.

Other Tests

Ophthalmologic evaluation may be useful if diplopia (seen in 10% of patients) is a presenting complaint or if papilledema (seen in 50% of patients) is found during the examination. Neuropsychological evaluation may be useful if memory loss or behavior change (found in 35-40% of patients) is a presentation.

Diagnostic Procedures

Lumbar puncture is typically contraindicated in patients with these lesions because of a risk of cerebral herniation in patients who demonstrate noncommunicating hydrocephalus.

Histologic Findings

Colloid cysts are lined with simple or pseudostratified epithelial cells. Their shape is either flattened cuboidal or low columnar, and they rest on a thin capsule of collagen and fibroblasts. The cysts are mucin secreting and ciliated. Cells are Periodic Acid-Schiff (PAS) and S100 positive, while Glial Fibrillary Acidic Protein (GFAP), vimentin, and neurofilament are negative. The stromal wall stains positively for vimentin. Contents of the cyst are usually greenish and of variable viscosity.

Medical Therapy

Medical treatment of these lesions is not appropriate or indicated if the patient is symptomatic.

Surgical Therapy

Surgery is often indicated for these lesions and should be performed in a timely manner. The goals are to relieve hydrocephalus and to remove the risk of deterioration in clinical status.

Preoperative Details

If the patient appears obtunded, urgent ventricular drainage is usually indicated and bilateral ventricular drainage may be frequently required as well. If no neurological deterioration has occurred and the patient is stable, CSF diversion is not indicated because enlarged ventricles can facilitate the surgical approach.

Intraoperative Details

The 3 approaches most commonly used are the transcortical approach, the interhemispheric transcallosal approach, and the endoscopic approach. Stereotactic drainage/aspiration has been used, but it is a blind technique that may fail because the cyst contents may be too viscous to drain. Furthermore, the recurrence rate is high because the cyst wall is usually retained. Similarly, the endoscopic approach has a higher rate of incomplete cyst resection, which may increase recurrence rates. Microsurgical resection through either the transcortical-transventricular or transcallosal approach is still considered the criterion standard for treatment of symptomatic patients with colloid cysts. [9]

Transcortical approach

The transcortical approach involves making a corticectomy over the middle frontal gyrus and proceeding to the frontal horn of the lateral ventricle. Intraoperative ultrasonography may aid in the approach to the ventricle. The use of tubular retractors in the brain may help create an operative corridor for the surgeon to work through. [1The foramen of Monro is visualized at the convergence of the septal veins, the thalamostriate vein, and the choroid plexus. The fornix arches over the superior and anterior margins of the foramen. Avoiding the fornix is important because unilateral fornix damage has been associated with amnesia (both anterograde and retrograde).

The cyst should be readily visualized through the foramen. The cyst is then punctured and the contents are aspirated, internally decompressing the walls of the cyst. Avoiding excessive retraction of the walls of the lateral ventricle is important because the genu of the internal capsule is in the subependyma. Other concerns include damaging the thalamostriate veins, which can result in basal ganglia damage. After the cyst has been decompressed, completely removing it to prevent recurrence is essential. Leaving a small portion of the cyst behind may occasionally be necessary if it is attached to either the thalamostriate or internal cerebral veins.

Interhemispheric transcallosal approach

The interhemispheric transcallosal approach avoids incising the cortex. A frontal (usually right) craniotomy is made from about two-thirds anterior to one-third posterior to the coronal suture, crossing the midline to expose the superior sagittal sinus. The right frontal lobe is then retracted laterally, and the corpus callosum is exposed. Draining cortical veins must be avoided if possible. The preoperative MRI can help identify potential veins. A 1-cm incision is made in the corpus callosum, allowing entry to the lateral ventricle. The foramen of Monro can then be visualized, and the septum pellucidum may be divided to look into the contralateral ventricle. Either ventricle may be entered through a standard right frontal transcallosal approach. Close inspection of the orientation of the choroid plexus, the caudate nucleus, and the foramen of Monro helps determine which of the ventricles has been entered.

Endoscopic approach

The endoscopic approach is the same as the transcortical approach, except that the former is accomplished through a burr hole. The cyst is punctured and aspirated through the working channels of the endoscope. Instrumentation is limited by the size of the working channels, as is the ability to perform bimanual tasks. Use of the endoscope also requires the presence of a fluid environment, which reduces visibility, clarity, and effectiveness of the cautery. Development of new technologies such as improved endoscopic cutting devices will continue to bridge the gap in performance with open surgical techniques. [2]

The endoscopic approach has the advantage of reducing operative time and hospital stay. In addition, the infection risk appears to be less than craniotomy. The primary drawback is the higher incidence of incompletely resected cysts leading to potential cyst regrowth and a need for additional procedures. Also, an endoscopic approach may potentially need to be converted into an open procedure because of difficulty in cyst aspiration or excessive bleeding. This possibility should be discussed with the patient and family prior to surgery. [39]

A combination of microsurgery and stereotactic guidance of a rigid endoscope overcomes many of the limitations of conventional open craniotomy and the pure endoscopic approach. [4The ventriculostomy is performed using stereotactic guidance, thus allowing the surgeon to approach the foramen of Monro with minimum trauma to the brain. A sheath can be placed, allowing sufficient room for placement of an endoscope. This also allows for specially designed instrumentation to be placed for dissection and electrocautery. Cerebrospinal fluid (CSF) can be removed, which improves visualization through the endoscope and also use of the instruments. Removal of the colloid cyst is the same as with conventional microinstruments. Depending on variations of anatomy, variations in technique have also been developed. In patients with a cavum septum pellucidum, the transcavum septum pellucidum interforniceal approach has been described, although the risk of bilateral forniceal injury is serious and must be avoided.

A common concern regarding the endoscopic approach is the possibility of cyst recurrence with remnants left during the original surgery. A study showed that these remnants do lead to a higher rate of cyst recurrence as compared with patients that had complete cyst removal. Furthermore, postoperative MRI was not sensitive to detecting coagulated cyst remnants that were noted in the operative report. The authors conclude that every attempt must be made to completely remove the cyst wall and contents. [25However, not all cyst recurrences are symptomatic or require repeat observation. In fact, many of these patients can be observed. Also, the relative risk of neurological injury from attempts at complete cyst removal versus that of recurrence is not known.

Postoperative Details

Each approach has specific risks and complications. The transcortical approach carries an increased incidence of epilepsy. The transcallosal approach decreases the risk of postoperative epilepsy but risks venous infarction and contralateral leg weakness from prolonged retraction. An extensive callosal resection may also cause temporary mutism. One study has indicated that restricting the callosal resection to 1 cm may reduce postoperative cognitive deficits. [5Excessive manipulation of the fornix may affect memory. The endoscopic approach is the least invasive, but it can be used only on cysts that can be aspirated. Large cysts cannot be removed with this technique. A steeper learning curve exists with the endoscopic technique. The endoscopic approach generally requires a shorter hospital stay, although similar results are seen with small craniotomies, which reduce operative time and hospital stay.

Hydrocephalus can persist after surgery, even after resection of the cyst. This may be secondary to spillage of the cyst contents or bleeding during surgery. Patients with long-standing hydrocephalus may lose compliance in their ventricular system and be left with persistently enlarged ventricles despite normal pressures. If there is a concern during surgery, a ventricular catheter can be placed intraoperatively to safeguard against ventricular dilatation or intraventricular hemorrhage. Patients can usually be weaned off the ventriculostomy, but in some cases a ventriculoperitoneal shunt may be needed.


Colloid cysts are usually cured after successful aspiration and complete resection. Hydrocephalus may develop despite removal of the cyst, and periodic CT scans should be performed.


Potential complications of surgery include seizures, postoperative hematoma, infection, venous infarct, memory deficit, mutism, and hemiplegia. In a series of 80 patients operated on by the transcallosal transforaminal approach, the complications encountered were postoperative seizures in 6, acute hydrocephalus in 4, venous cortical infarct in 4, transient hemiparesis in 4, transient memory impairment (especially for immediate recall) in 9, mutism in 1, subdural hematoma in 1, meningitis in 3, and tension pneumocephalus in 1. There were 2 deaths. [10]

Outcome and Prognosis

Preoperative function partly determines patient outcome; most patients tolerate resection well.

Future and Controversies

With an increasing emphasis on noninvasive therapies, the endoscopic approach is becoming more popular. In the opinion of the authors, the open surgical approach provides the safest exposure with controlled resection of the cyst. The illumination and magnification provided by the operating microscope allow more precise coagulation and dissection of critical structures than afforded by endoscopy.

As endoscopic technology continues to improve, the outcomes with endoscopy is now rivaling traditional craniotomy. The importance of complete cyst resection is still under debate. Certainly, leaving cyst remnants leads to a higher rate of recurrence, but the neurological cost to the patient of aggressive attempts at cyst removal needs to be weighed against a higher recurrence rate; not all cyst recurrences require surgery.

Lastly, radiosurgery is not known to be effective for colloid cysts. In most cases, this disease entity still requires a surgical treatment.