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Neurosurgery > Neoplasm
Colloid Cysts
Article Last Updated: Jan 7, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Lawrence S Chin, MD, FACS, Professor and Chairman, Department of Neurosurgery, Boston University School of Medicine; Neurosurgeon-in Chief, Boston Medical Center
Lawrence S Chin is a member of the following medical societies: Alpha Omega Alpha, American Association for Cancer Research, American Association for the Advancement of Science, American Association of Neurological Surgeons, American College of Surgeons, Children's Oncology Group, Congress of Neurological Surgeons, Phi Beta Kappa, and Society for Neuro-Oncology
Coauthor(s):
Mayur Jayarao, MD, Fellow, Department of Neurosurgery, Boston Medical Center
Editors: Scott C Dulebohn, MD, Assistant Professor, Department of Surgery, Division of Neurosurgery, University of Minnesota College of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Ryszard M Pluta, MD, PhD, Associate Professor, Neurosurgical Department Medical Research Center, Polish Academy of Sciences at Warsaw, Poland; Senior Researcher, Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, NIH; Herbert H Engelhard III, MD, PhD, Director, UIC Neuro-Oncology Program, Chief, Division of Neuro-Oncology, Associate Professor, Department of Neurosurgery, University of Illinois at Chicago; Allen R Wyler, MD, Medical Director, Northstar Neuroscience, Inc
Author and Editor Disclosure
Synonyms and related keywords:
colloid cysts, neuroepithelial cyst, paraphyseal cyst, obstructive hydrocephalus, primary brain tumors, intraventricular masses, increased intracranial pressure, hydrocephalus, anterior third ventricle, increased intracranial pressure
History of the Procedure
In 1858, Wallmann first reported on colloid cysts. In 1921, Dandy accomplished the first successful resection of a colloid cyst.
Problem
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.
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.
Etiology
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.
Pathophysiology
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.
Clinical
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.
Lab 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 homogenous, 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.
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. MRI
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.
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.3 In contrast, 63% of patients with high-signal lesions were easy to aspirate. This differentiation may be useful in preoperative planning and management.
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
Lumbar puncture is absolutely contraindicated in patients with these lesions because of a risk of cerebral herniation.
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 nor 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. Further, the recurrence rate is high because the cyst wall is usually retained. 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 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 see the contralateral foramen. 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.
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. The 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 higher risks are involved.4
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. Excessive 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 can not be removed with this technique. A steeper learning curve exists with the endoscopic technique.
Hydrocephalus can persist after surgery, even after resection of the cyst. This complication may be secondary to spillage of the cyst contents or to bleeding during surgery. A ventricular catheter may be placed intraoperatively to safeguard against ventricular dilatation.
Follow-up
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.
Preoperative function partly determines patient outcome; most patients tolerate resection well.
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 evolves, the role of endoscopy may become more prominent. Radiosurgical treatments are not known to be effective for colloid cysts.
| Media file 1:
Axial CT scan that shows a colloid cyst with associated hydrocephalus. |
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| Media file 2:
Coronal MRI shows a colloid cyst in the roof of the third ventricle. The patient has mild hydrocephalus. |
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Media type: MRI
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| Media file 3:
Intraoperative 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. |
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| Media file 4:
Intraoperative photograph that shows removal of the cyst, leaving a dilated Monro foramen The third ventricle can be seen through the opening. |
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Media type: Photo
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Colloid Cysts excerpt Article Last Updated: Jan 7, 2008
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