Keywords
epidermoid cyst - fourth ventricle - hydrocephalus
Introduction
Intracranial epidermoid cysts (ECs) consist of slow-growing congenital lesions. Initially
described by French pathologist Cruveilhier as the ‘most beautiful of all tumors’
based on their pearly nature,[1] ECs are originate from malformations associated with surface elements of the nervous
system ectoderm during the neural sulcus closure, or from the formation of secondary
cerebral vesicles.[2]
Because they grow slowly, they usually do not become symptomatic until the patient
has reached the third or fifth decades of life. They develop through the progressive
accumulation of keratin and cholesterol, produced by the peeling of the epithelium
that surrounds the cyst.[3]
The occurrence of ECs is rare, making up to ∼ 0.2% to 1.8% of central nervous system
(CNS) tumors.[1] Classically, they are located more frequently in the following sites: the cerebellopontine
angle (corresponding to half of the cases), the temporal fossa, and the suprasellar
and quadrigeminal regions. Implantation in the cisterna magna region and the fourth
ventricle is even rarer.[4] Approximately 5% of ECs affect this location.[5] According to Sengupta and Singh,[6] there are only about 100 reported cases of epidermoid tumors of the fourth ventricle.[6]
Structurally, ECs are formed by a white, pearly tissue, which is coated by a capsule
adhered to adjacent structures. The cystic content is avascular, and presents a material
resembling candle wax arranged in concentric lamels.[7] The lesion grows slowly, and has a flexible and deformable appearance, adapting
to the space in which it develops.[8]
The tomographic aspect of this lesion is typical of a hypodense extra-axial mass,
which is not impregnated by venous contrast. Upon magnetic resonance imaging, they
may present a similar signal or a slight increase regarding cerebrospinal fluid (CSF)
in the T1 and T2 ponderations. The main differential diagnosis is made in relation
to the arachnoid cyst, and the distinction is usually made with sequences of fluid-attenuated
inversion recovery (FLAIR) and diffusion. The arachnoid cyst follows the intensity
of the CSF signal in all sequences, while epidermoid tumors are not hypointense in
the FLAIR, showing areas of hypersignal in relation to the CSF. In diffusion sequences,
epidermoid tumors typically have diffusion restriction, unlike arachnoid cysts.[9]
The ideal treatment is the removal of the cystic component with complete resection
of the capsule, taking care not to compromise the neurological condition of the patient.[4] Although the contents of the cyst can be easily aspirated, the total removal of
the tumor is not always possible due to the fact that the capsule is usually adhered
to neighboring neurovascular structures.[10]
Aseptic meningitis, a complication that may occur postoperatively, can be avoided
by preventing the extravasation of the cystic content into the surrounding subarachnoid
space.[10] Irrigation of the surgical bed with corticoids has been reported as a form of aseptic
meningitis prevention.[11]
The rate of recurrence is between 1% and 54%, and it can be avoided by devitalizing
the remaining fragments of the capsule during surgery.[11] The surgical reapproach is usually performed for decompression. Malignant degeneration
has been reported in cases of recurrent epidermoid tumors.[4]
The objective of the present article is to report a case of EC of the posterior fossa
affecting the interior of the fourth ventricle with extension to the cisterna magna.
Its presentation, radiological image and surgical management will be described.
Case Report
A 31-year-old female patient, who started with dysmetria, gait disorder, diplopia
and dizziness one year previously, evolved with progressive headache over the last
3 months, associated with vomiting and loss of visual acuity. A computed tomography
scan of the skull revealed a hypodense lesion located inside the fourth ventricle
causing obstructive hydrocephalus. Initially, the patient was submitted to a ventriculoperitoneal
shunt, with symptomatic improvement after the procedure, especially with regards to
the headache and visual loss. With the stabilization of the neurological condition
after intracranial hypertension treatment in emergency services, the patient was referred
to our service for a complementary radiological study, aiming to enable the surgical
approach of the lesion.
On the neurological admission examination, the presence of gait ataxia, positive Romberg
sign, more pronounced dysmetria on the left, dysdiadochokinesia, nystagmus and paralysis
of the sixth cranial pair on the left was verified.
On the magnetic resonance imaging, it was possible to observe an expansive extra-axial
formation with epicenter in the cerebellar cistern measuring 4.1 cm × 4.9 cm × 4.2 cm,
isointense to CSF in T1 and T2 ([Figs. 1] and [2]). The aforementioned lesion did not present postcontrast enhancement ([Fig. 1b]). The lesion compressed the bridge, the bulb, the IV ventricle, and the cerebellar
hemispheres, and was more pronounced on the left. There was inferior insinuation of
the lesion along the foramen magnum for ∼ 9 mm. The heterogeneous signal in the FLAIR
and especially the diffusion restriction made it possible to indicate EC as the main
diagnostic hypothesis ([Fig. 3]).
Fig. 1 Magnetic resonance imaging: axial cut showing cystic lesion inside the IV ventricle,
measuring 4.1 cm × 4.9 cm × 4.2 cm. (A) T1 sequence without contrast evidencing a hypointense injury, slightly heterogeneous,
and with a slightly larger signal from the cerebrospinal fluid. (B) Absence of enhancement after contrast administration.
Fig. 2 Magnetic resonance with T2 weighting. The lesion is hyperintense, similar to the
cerebrospinal fluid. (A) Sagittal cut; and (B) axial cut.
Fig. 3 Magnetic Resonance imaging: axial cut showing (A) heterogeneous signal in the FLAIR, and (B) a hyperintense signal in the restriction, making the epidermoid cyst the main diagnostic
hypothesis.
The patient underwent suboccipital craniectomy to access the posterior fossa. After
opening the dura mater, a whitish and pearly lesion was found, emerging from the bulbo-cerebellar
fissure ([Fig. 4]). We performed the emptying of the lesion that occupied the interior of the IV ventricle
([Fig. 5]). The surgical procedure went uneventful.
Fig. 4 Intraoperative finding. Whitish and pearly lesion emerging from the bulbo-cerebellar
fissure.
Fig. 5 Intraoperative findings. Emptying of the cyst, with a view of the floor of the IV
ventricle (bridge and bulb) on the deep margin of the lesion.
The postoperative period progressed satisfactorily, with improvement of the previous
symptomatology. The results of the anatomopathological examination were consistent
with EC. The patient was discharged on the 11th day after surgery. In a return consultation
performed ∼ 3 months after surgery, she was already walking without help, maintaining
progressive improvement. The magnetic resonance imaging on this occasion revealed
complete emptying of the lesion located in the IV ventricle ([Fig. 6]).
Fig. 6 Magnetic resonance imaging with diffusion weighting, evidencing the dissection of
the cystic cavity with anatomical restoration of the IV ventricle.
Discussion
Epidermoid cysts constitute congenital, benign and rare lesions. They correspond to
∼ 0.2% to 1.8% of all intracranial tumors.[12] There is preponderance among females. The most frequent locations of these processes
are: the cerebellopontine angle and the parasellar region; other rarer locations include
the brainstem and the fourth ventricle.[13] They are located in the fourth ventricle only in 5% of the cases, denoting unusual
topography. There are only ∼ 100 cases of this location described in the literature.[5]
[6]
Epidermoid cysts are tumors of very slow growth, with a growth pattern like that of
epidermal skin cells. They develop from the remaining elements of the epidermis during
the closure of the neural sulcus and the disjunction of the surface ectoderm with
the neural ectoderm, between the third and fifth weeks of embryonic life.[11] Despite its genesis in intrauterine life, the moment of diagnosis is usually established
between the third and fifth decades of life, the age group of the patient in the case
herein reported.
Clinically, cerebellar syndrome is the main responsible disease for the initial symptomatology,
while intracranial hypertension syndrome is less common, since hydrocephalus, which
occurred in the case herein reported, is of late onset, and is observed in less than
50% of the cases.[14] Although the extravasation of cystic content to the subarachnoid space has been
shown to cause aseptic meningitis, no signs of meningeal irritation were observed.
Preoperative magnetic resonance imaging was fundamental for the establishment of the
diagnostic hypothesis of EC. The lesion showed no contrast enhancement, and showed
a signal similar to CSF in the T1 and T2 ponderations; however, it was restricted
to diffusion, differentiating itself from other diagnostic possibilities, such as
arachnoid and tumor cysts.
Two complications may alter the course of the disease: aseptic meningitis and malignant
transformation. In order for aseptic meningitis to occur, a simple contact of the
cystic content with the CSF can be enough. The treatment of this condition includes
repeated lumbar punctures and corticoids.[15] This situation was not observed in the case of the patient in question.
On the other hand, malignant transformation is an extremely rare complication, and,
when present, is associated with the development of squamous cell carcinoma. In the
case of incomplete removal of the lesion, the growth of the remnant tumor is as slow
as that of the primitive tumor, requiring annual follow-up through magnetic resonance
imaging to evaluate its development potential.[15] Some studies have indicated radiotherapy as an alternative to the failure in surgical
treatment or recurrence, and tumor control can be achieved through this method.[16]
Conclusion
Epidermoid cysts constitute congenital, benign and rare lesions, corresponding to
∼ 0.2% to 1.8% of all intracranial tumors, and they are located in the fourth ventricle
only in 5% of the cases. Despite their genesis in intrauterine life, they are generally
diagnosed between the third and fifth decades of life as a result of their very slow
growth pattern. They develop from the malformations of the ectoderm during the closure
of the neural sulcus, between the third and fifth weeks of embryonic life. The diffusion-weighted
image of the magnetic resonance imaging was fundamental for the establishment of the
diagnosis. The ideal treatment consists of emptying the cystic content with complete
resection of the capsule, although it is not always possible when the capsule is firmly
adhered to important structures. Radiological follow-up is necessary in the postoperative
period to evaluate the recurrence, although malignant transformation is rare, and
reoperation has, above all, a decompressive character for symptom relief.
