Keywords
epidermoid cyst - hemorrhagic epidermoid cyst - vermian epidermoid cyst - midline
posterior fossa
Introduction
Intracranial epidermoid cysts (ECs) are rare congenital intracranial neoplasms accounting
for approximately 1.5% of all intracranial tumors. Pathophysiologically, ECs arise
from inclusion of ectodermal epithelial elements and grow by the accumulation of keratin
and cholesterol crystals, which are breakdown products created by the desquamation
of epithelial cells.[1] ECs tend to spread across the basal surface of the brain with a paramedial preference
such as the cerebellopontine angle and the parasellar region, and usually reach large
size before patients become symptomatic.[1]
[2] Midline posterior fossa ECs involving the cerebellar vermis are rare and have only
been reported in isolated reports when accompanied with hemorrhage. When hemorrhage
occurs in EC, the diagnosis is challenging and there is a potential for misdiagnosis.
Total resection of EC is usually the definitive treatment with very low recurrence
rate.
In this case report we describe the clinical characteristics of a patient with a hemorrhagic
vermian EC. In addition, an overview of all similar published cases is presented.
We systematically reviewed English written literature using PubMed database to search
for relevant English language articles published up to November 2019. All eligible
studies were analyzed, and the references were checked for additional relevant publications.
Information and data were extracted from all included literature. To the best of our
knowledge, our case represents only the sixth reported case of hemorrhagic vermian
EC in the English written literature.
Case Report
A 57-year-old deaf-mute female was admitted to our department with a short history
of repeated loss of consciousness. Neurologic examination revealed global passivity
with inability to walk. Computed tomography (CT) revealed a midline infratentorial
hyperdense lesion located in the cerebellar vermis causing compression of the fourth
ventricle with no surrounding edema. On axial CT scan obtained with a bone setting,
a small-calcified spot was present at the border of the lesion, but no hyperplasia
or erosion of the adjacent bone was seen. Obstructive hydrocephalus was present ([Fig. 1]). Magnetic resonance imaging (MRI) showed atypical cystic tumor with hemorrhagic/high-protein
content and vascularized nodus corresponding to calcified lesion on CT. On T1-weighted
and T2-weighted images the lesion was hyperintense and hypointense, respectively and
demonstrated no contrast enhancement. Due to tumorous expansion, syrinx of cervical
spinal cord was present ([Fig. 2]). The patient was operated on under general anesthesia. At first, external ventricular
drain was inserted, with intraventricular pressure been only 60 mm of water column.
Then, wide suboccipital craniotomy and laminectomy of the first cervical vertebra
were performed in a semi sitting position. Dark cyst with a greenish mud-like debris
content was identified ([Fig. 3]), and the entire cyst wall with its content was completely removed. Grossly, no
hair or yellow cheesy sebaceous material was present. Histological examination revealed
organizing blood clot and lightly basophilic lamellar keratin with dystrophic calcifications
and heterotopic ossification. Few strips of squamous epithelium immunohistochemically
positive for CK5/6 and P40 were identified. No dermal skin appendages, such as hair
follicles or sebaceous glands were present ([Fig. 4]). According to imaging studies, intraoperative characteristics, and histological
examination of the diagnosis of hemorrhagic EC were established. Postoperatively,
there was a rapid improvement of neurological status and the patient was immediately
alert and able to walk. There were no signs of chemical meningitis in the postoperative
period. Control MRI scan showed radical resection of the tumor.
Fig. 1 CT scan of hemorrhagic vermian EC. Native CT scan in axial plane (a) and sagittal plane (b) revealed a midline infratentorial hyperdense lesion causing compression of the fourth
ventricle and brainstem. CT scan with bone setting (c) revealed a small, calcified spot (white arrow). CT, computed tomography; EC, epidermoid cyst.
Fig. 2 MRI of hemorrhagic vermian EC. MRI showed a lesion located in cerebellar vermis—hyperintense
on T1-weighted images (a) and hypointense on T2-weighted images (b). On T1-weighted imaging with gadolinium in sagittal plane (c) the tumor did not show any contrast enhancement. EC, epidermoid cyst; MRI, magnetic
resonance imaging.
Fig. 3 Intraoperative microscopic view of hemorrhagic vermian EC. Via midline suboccipital
craniotomy we identified a dark cyst with a greenish mud-like debris. (a,b) The supposed calcified fragment (white arrow, a). During the procedure, a few pearl-like particles were found on the periphery of
the lesion (black asterisks, c). During the procedure, a gross total resection was achieved.
Fig. 4 Histological features of hemorrhagic EC. Microscopic examination revealed organizing
blood clot (a, hematoxylin-eosin), and lightly basophilic keratin lamellae (b, hematoxylin-eosin), with dystrophic calcifications and heterotopic ossification
(c, hematoxylin-eosin). Only few strips of benign squamous epithelium were found, with
no adnexal structures (d, hematoxylin-eosin). The epithelium was immunohistochemically positive for squamous
markers CK5/6 (d, inset) and P40. EC, epidermoid cyst.
Discussion
Intracranial ECs, also known as pearly tumors are congenital avascular intracranial
neoplasms that account for approximately 1.5% of all intracranial tumors and 7 to
9% of all cerebellopontine angle tumors.[1]
[2]
[3]
[4] ECs are thought to result from aberrantly located ectodermal cells, that have been
entrapped during the process of neurulation in the period between the third and fifth
gestational weeks. Typical slow and linear rate of growth of EC is caused by accumulation
of desquamated keratin, cellular debris, and cholesterol crystals. Slow progression
of EC permits presentation of EC at large sizes and prolonged symptomatology.[2] Symptoms are generally attributed to effects of a space-occupying lesion. Infrequently,
EC may present with a history of recurring aseptic (chemical) meningitis caused by
spontaneous rupture of the highly irritative cyst contents into the subarachnoid space.
The preference for paramedian location and histological constituents differentiates
epidermoid from dermoid cysts, which are more likely to be situated along midline
structures and microscopically contain dermal appendage.[1]
[2]
[5] Consequently midline posterior fossa EC involving the cerebellar vermis are uncommon.[2]
[6] Treatment of EC consists of complete microsurgical removal of cyst lining and its
content. However, complete excision may be challenging, especially when the tumor
and neurovascular structures are closely apposed. In such cases, subtotal removal
of the cyst is advocated.[1]
[2]
[5]
On CT imaging, typical EC is described as hypodense and well demarcated lesion. Calcifications
are rarely described, and when present, usually marginally located. On MRI ECs usually
present as hypointense and hyperintense on T1 and T2-weighted images, respectively
without contrast enhancement due to the absence of a well-developed vascular network,[1]
[2]
[5]
[7]
[8] although minor rim enhancement has been reported.[3] Diffusion-weighted imaging shows intense signal as a result of restriction of water
movement and this diffusion restriction differentiates EC from other cystic lesions.[8] Intraoperatively ECs are typically well-defined lesions with an irregular nodular
outer surface and a shiny mother of pearl appearance. Microscopically, the wall of
the EC consists of a layer of stratified squamous epithelium without vascularity.[7] Due to avascular nature of EC, intralesional hemorrhage is extremely rare and has
only been reported a few times.[3]
[4]
[5]
[6]
[7]
[9]
[10]
[11] In our literature review, we found five cases of vermian hemorrhagic EC with our
case to be the sixth ([Table 1]).
Table 1
Review of published hemorrhagic vermian ET
|
Case no. (author)
|
Age (years), Sex
|
CT/MRI findings
|
Cyst contents
|
Extent of resection
|
Outcome/F-U
|
|
1.[5]
|
24, F
|
Diameter: 4 cm
CT: not specified
MRI: not specified
preoperative dg.: epidermoid.
|
Old bleeding, yellow cheese-like
|
GTR
|
No neurologic deficit, F-U not mentioned.
|
|
2.[5]
|
43, F
|
Diameter: 5 cm.
CT: not specified.
MRI: not specified.
preoperative dg.: epidermoid.
|
Old bleeding, yellow cheese-like
|
GTR
|
No neurologic deficit, F-U not mentioned.
|
|
3.[9]
|
21, M
|
Diameter: not noticed.
CT: hyperdense lesion.
MRI: T1 hypointense + hyperintense nodule.
T2 hypointense + hyperintense nodule.
CE: no
preoperative dg.: not mentioned.
|
Mud-like, cheesy debris
|
GTR
|
No neurologic deficit, 1 y.
|
|
4.[6]
|
30, F
|
Diameter: not specified.
CT: hyperdense lesion.
MRI: not noticed.
preoperative dg.: hemorrhage to tumor.
|
Brownish cheesy
|
GTR
|
No neurologic deficit, 4 y.
|
|
5.[4]
|
19, F
|
Diameter: 6 cm
CT:hyperdense lesion with small-calcified spot.
MRI: T1 hypointense + hyperintense nodule.
T2 hypointense + isointense nodule.
CE: nodule enhancement
preoperative dg.: not mentioned.
|
Greenish tumor
|
GTR
|
No neurologic deficit, F-U not mentioned.
|
|
6. Presented case
|
57, F
|
Diameter 5 cm
CT: hyperdense lesion with small-calcified nodule.
MRI: T1 hyperintensive
T2 hypointensive
CE: no
preoperative dg.: vascular lesion (AVM, cavernoma).
|
Greenish mud-like debris, crystals
|
GTR
|
No neurologic deficit, 6 mo.
|
Abbreviations: AVM, arteriovenous anomaly; CE, contrast enhancement; F-U, follow-up;
GTR, gross total removal.
It was proposed that hemorrhage within an EC may arise from the richly vascularized
granulation tissue, that forms in response to the leakage of the irritative cyst content
and resultant inflammation.[10] Occasionally, granulation tissue is responsible for the firm adherence of the capsule
to the surrounding neurovascular structures.[1] Ren et al found hemorrhage in granulation tissue in 90.5% of cases in their series
of EC with hemorrhage.[5] Similarly Hasegawa et al surmised that bleeding into the cyst originated in the
fibrous nodules of the cyst wall, which contained vessels.[12] Clotted blood, hemosiderin-laden macrophages, and neurovascularity in the cyst wall
granulation tissue were also found in a case reported by Hsieh.[11] According to Xiaohui et al, the pathogenesis of hemorrhage in the granulation tissue
has two explanations. The first explanation is that the hemorrhage results from the
mechanical tearing of the vascularized granulation tissue patches due to the outgrowth
of the cyst contents. The second explanation is that hemorrhage results from the erosive
degeneration of the vessels caused by the contents of the cyst.[5]
Hemorrhage into EC makes diagnosis quite challenging. Hyperdensity seen CT, that refers
to hemorrhage, is not characteristic. Moreover, various authors reported hyperdensity
of intracranial EC, caused by high-concentrated protein content of the cyst.[3]
[4]
[6]
[13] In the series by Li et al, hyperdense EC represented 3% of all cases. The authors
assumed that recurrent leakage of the cyst contents and a subsequent chemical inflammatory
response may be responsible for the high density of some EC on CT.[4] Likewise, causes of atypical signal changes present on MRI, except of hemorrhage,
include calcification and increased protein concentration as a result of inflammation
or infection.[3]
[5] Importantly, sudden development of symptoms and exponential growth of EC with a
novel finding of contrast enhancement seen on imaging studies may suggest malignant
transformation.[2]
[4]
[14]
[15]
[16]
[17]
Although extremely rare, malignant transformation into squamous cell carcinoma confers
poor prognosis.[16] Careful histological examination of hyperdense EC lesions is essential to differentiate
EC from other diseases, and to rule out malignant transformation, which would require
adjuvant therapy after surgery.[9]
Conclusion
Hemorrhagic vermian ECs are rare and diagnostically challenging lesions. Gross total
resection is the goal of surgical treatment and when ECs are located in cerebellar
vermis this is often fully achieved. Histological examination is crucial to rule out
malignant changes.
