Keywords
colloid cyst - fourth ventricle - hemorrhage
Introduction
Colloid cysts comprise around 0.5 to 1% of all primary brain tumors.[1]
[2] These rare benign cystic tumors are endodermal embryological remnants, frequently
situated on the roof of the third ventricle. Their occurrence within the fourth ventricle
is unusual.[3] The clinical manifestations vary, ranging from incidental detection of cysts to
instances of sudden fatality due to rapid-onset hydrocephalus.[1]
[4]
Typically measuring 0.3 to 4 cm in size, these cysts possess a distinct cyst wall,
display well-defined boundaries, and expand due to amorphous and protein-rich fluid
secretions.[2] On computed tomography (CT) scans, they appear homogeneously hyperdense, while on
magnetic resonance imaging (MRI), they exhibit high T1 signal intensity and low T2
signal intensity.[5] Instances of acute hemorrhage occurring within colloid cysts are exceedingly uncommon
and can manifest with sudden, severe symptoms or even lead to abrupt demise.[6]
[7] In this article, we present a remarkable case of a patient harboring an unconventional
colloid cyst within the fourth ventricle and presenting with acute worsening of symptoms.
This patient exhibited intracystic hemorrhage, prompting the consideration of alternative
diagnoses. To our knowledge, intracystic hemorrhage in colloid cyst of the fourth
ventricle has never been documented.
Case Report
A 55-year-old woman presented with intermittent headaches and occasional vertigo over
the past 2 months. Since last week, she had persistent headaches of throbbing variety,
accompanied by vomiting and gait imbalance. During the physical examination, no focal
neurological deficits were noted. CT of the brain spotted a hyperdense mass in the
fourth ventricle with mild upstream dilatation of ventricles. The contents showed
attenuation values of 80 to 95 HU. MRI of the brain demonstrated a distinct, well-defined
mass in the posterior part of the fourth ventricle that measured approximately 3.3 × 2.4 × 2.5 cm
in all dimensions. The lesion appeared hypointense on T2 and fluid attenuated inversion
recovery (FLAIR) images, displayed intermediate characteristics on T1 images, and
exhibited blooming on susceptibility-weighted images. A small, irregularly enhancing
mural nodule was evident on the left posterior side on contrast-enhanced images ([Fig. 1]). The MRI findings suggested the possibility of a lesion with hemorrhagic or calcific
attributes and raised suspicion of it being a hemangioblastoma, ependymoma, or metastatic
lesion.
Fig. 1 Preoperative images. (A) Axial view of the computed tomography (CT) of the brain showing hyperdense lesion
in the region of the fourth ventricle. Axial views of the magnetic resonance imaging
(MRI) of the brain showing lesion in the fourth ventricle displaying (B) heterogeneous intensity on T1 and (C) hypointense on T2. (D) The lesion does not take contrast on T1 + C images. There is blooming on (E) susceptibility-weighted imaging (SWI) without any diffusion restriction on (F) diffusion-weighted imaging (DWI).
The patient underwent suboccipital craniotomy and the telovelar approach, which revealed
a grayish–white spherical smooth cystic mass with a thin capsule. The cyst was found
within the fourth ventricle and could be separated from its surroundings through a
clear plane of cleavage, except for its attachment to the vermis. The cyst contained
a thick, sticky, gelatinous, brownish content with noticeable vascularity ([Fig. 2A, B]). The cyst was excised completely except for its posterosuperior attachment to the
vermis. On follow-up at 1 month, the patient is doing well with resolution of headaches
and vertigo.
Fig. 2 (A, B) Intraoperative images showing the telovelar approach with tonsils (*) and vermis
(#) in view. A thin-walled cyst containing hemorrhage-stained gelatinous content is
also visible. (C) Histopathology showing the cyst wall lined by a cuboidal epithelium with a subepithelial
xanthogranulomatous reaction.
Upon histopathological analysis, the cyst wall was observed to be lined variably with
two to three layers of cuboidal to multilayered squamous lining cells, accompanied
by regions of hypocellular collagenous tissue. The cyst content consisted of a homogenous,
colloidlike material. Notably, the existence of red blood cells, macrophages laden
with hemosiderin, chronic inflammatory cells, and cholesterol crystals indicated hemorrhage
within the colloid cyst.
Discussion
Colloid cysts are characterized by their benign nature and thin walls, with a preferential
location along the midline of the third ventricle, in proximity to the foramen of
Monro. These cysts are filled with colloid material.[8]
[9] They originate from the residual endodermal embryonic structures within the brain.
Other potential sites include diencephalic ependymoma, the invagination of the neuroepithelium
within the ventricle, or the respiratory epithelium of endodermal origin.[5]
[10]
[11] These cysts account for about 15 to 20% of intraventricular masses and 0.5 to 1.0%
of all primary brain tumors.[4]
[10]
[11]
The utilization of CT and MRI has led to an increased identification of asymptomatic
colloid cysts.[10] Common symptoms, often linked to heightened intracranial pressure in the third ventricular
cysts, include headaches, memory impairments, and cognitive impairments.[5]
[8]
[10] Additional modes of presentation encompass dementia, disruptions in gait, and urinary
incontinence due to chronic hydrocephalus. Colloid cysts can give rise to significant
morbidity and, in some cases, even mortality. The potential causes include acute obstructive
hydrocephalus and, in rare instances, intracystic hemorrhage referred to as “cyst
apoplexy.”[8]
[9]
[12] The occurrence of hemorrhagic changes within colloid cysts can cause rapid enlargement,
ultimately leading to a sudden and total obstruction of cerebrospinal fluid (CSF)
circulation.[6]
[13]
There have been a handful of events of hemorrhagic third ventricle cysts described
in the literature. However, a hemorrhagic colloid cyst, especially one within the
fourth ventricle, has never been reported. A slow-growing cyst does not manifest clinically,
as the intracranial pressures are maintained within normal ranges for longer periods
of time despite progressive enlargement of the ventricles. On the contrary, rapid
expansion of the cyst in cases of cyst apoplexy may lead to elevated intracranial
pressure, resulting in clinical symptoms.[12] This occurs as a result of failure of the CSF dynamics to adjust to sudden changes
in cystic volume.[4] The symptoms of headache and vertigo in our patient can be attributed to a mass
lying within the fourth ventricle. Intracystic hemorrhage is assumed to be a potential
cause of rapid lesion expansion and the sudden worsening of symptoms in our case;
however, there is no way to establish it, and the precise reason remains unknown.
On CT scan, colloid cysts usually present as hyperdense, rarely as isodense, and exceptionally
rarely as hypodense. This density variation is contingent upon the cholesterol content
within the cyst.[6]
[14] On MRI, hyperintensity on T1-weighted images is typical and reflects cholesterol
levels, while the degree of protein fluid determines signal intensity on T2-weighted
images, which generally appears isointense to hypointense. Importantly, these cysts
usually do not suppress on FLAIR studies and demonstrate absence of diffusion restriction
on diffusion-weighted imaging.[5]
[6]
[14] In our case, the signal intensity on T1 and T2 aligns with the literature. However,
notable heterogeneity in signal intensity on T2-weighted images, accompanied by blooming
artifacts on susceptibility-weighted imaging (SWI), corresponds to the confirmed cystic
hemorrhage.
The underlying cause of intracystic bleeding remains elusive. While hypertension and
coagulation disorders have been proposed as potential factors, concrete proof is lacking
in most cases.[2]
[9]
[11]
[12] However, in the majority of cases, including ours, the cause of the hemorrhage remains
unclear due to a lack of any significant medical history.
Management strategies for colloid cysts vary. Many reports have shown that rapidly
addressing hydrocephalus through emergency external ventricular drainage followed
by elective cyst removal yields satisfactory outcomes.[5]
[7]
[10] Stable patients can undergo direct cyst excision without the need for emergency
ventricular drainage,[11] as was the case in our situation.
Surgical procedures for symptomatic colloid cysts usually involve open microsurgical
or endoscopic techniques for excision.[11] For the common third ventricular colloid cyst, the preferred method is the interhemispheric
transcallosal approach. An alternative is the endoscopic approach, which has been
considered advantageous over the microscopic method due to its exceptional vision
and minimally invasive entry through the enlarged ventricles.[10] Also, rates of gross total resection are higher, and recurrence and reoperation
are lower in the endoscopic approach as compared to the microscopic approach, as reported
by Sheikh et al in their analysis of outcomes in 1,278 patients.[15] Stereotactic aspiration is also a minimally invasive option in third ventricular
colloid cysts with thin contents; however, it has fallen out of favor due to chances
of recurrence.[10]
A hemorrhagic colloid cyst may alter the recommended course of therapy, depending
on its size and location.[9]
[10] Surgery for cystic lesions of the fourth ventricle often consists of suboccipital
craniotomy for direct cyst excision, endoscopic fenestration, or ventricle shunting.
Endoscopic removal of cysts in the fourth ventricle has also been reported. On the
other hand, the endoscopic method appears to be more difficult and needs special expertise,
especially when the cyst is attached to the ependymal lining or when there is a thin
aqueduct.[16] In contrast to colloid cysts in the third ventricle, the location of the cyst in
our case obviated the use of endoscopy or stereotactic aspiration. Our recommended
treatment plan was suboccipital craniotomy and the telovelar approach with microsurgical
excision due to the cyst's size and hemorrhagic nature, as well as additional differentials
to be addressed. We favor the use of microscopic surgery in cases of a hemorrhagic
cyst due to the potential challenges of aspirating thick clots and gelatinous material.
During microsurgery, the sticky gelatinous content and dense clot necessitate a sequential,
gradual piecemeal decompression and capsular dissection approach similar to that used
for fourth ventricle tumors, evading any harm to the crucial neighboring structures.
Conclusion
A hemorrhagic fourth ventricle colloid cyst is a rare entity and has never been described
in the literature. Preoperative radiological diagnosis can be challenging due to wide
variations in CT and MRI scans, and a colloid cyst should be considered a differential
in hyperdense lesions of fourth ventricle masses to avoid any intraoperative surprises.
Intracystic hemorrhage should be considered a plausible explanation for acute deterioration
of a patient with a colloid cyst. Expedited management and a microsurgical approach
are recommended in the treatment of hemorrhagic colloid cysts.
