Radio-pathological characteristics of malignant transformation of an epidermoid cyst in the cerebellopontine angle: A case report
- Department of Neurosurgery, Tokyo Medical University, Tokyo, Japan.
Michihiro Kohno, Department of Neurosurgery, Tokyo Medical University, Tokyo, Japan.
DOI:10.25259/SNI_1226_2021Copyright: © 2022 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Hiroki Sakamoto, Jiro Akimoto, Masateru Tsutsumi, Ken Matsushima ken, Norio Ichimasu, Michihiro Kohno. Radio-pathological characteristics of malignant transformation of an epidermoid cyst in the cerebellopontine angle: A case report. 08-Apr-2022;13:135
How to cite this URL: Hiroki Sakamoto, Jiro Akimoto, Masateru Tsutsumi, Ken Matsushima ken, Norio Ichimasu, Michihiro Kohno. Radio-pathological characteristics of malignant transformation of an epidermoid cyst in the cerebellopontine angle: A case report. 08-Apr-2022;13:135. Available from: https://surgicalneurologyint.com/surgicalint-articles/11515/
Background: Intracranial epidermoid cysts are rare congenital neoplasms that are clinically indolent and histologically benign. They rarely show malignant transformation, and several such cases have been reported. Some radiological features that suggest malignant transformation have been reported. However, histopathological features that indicate a high risk of malignant transformation have not been reported to date.
Case Description: We report a 59-year-old woman with a benign epidermoid cyst in the cerebellopontine angle that showed malignant transformation after 6 years. Magnetic resonance imaging (MRI) at the time of initial onset displayed a high-intensity signal on diffusion-weighted imaging (DWI), no peritumoral edema, and no enhancement on contrast-enhanced T1-weighted imaging. On the other hand, MRI at the time of malignant transformation showed a low-intensity signal on DWI, peritumoral edema, and enhancement of the tumor capsule on contrast-enhanced T1-weighted imaging. Pathological findings at the time of the first surgery differed from normal benign epidermoid cysts, in that stratified squamous epithelial metaplasia was observed, and immunohistochemical (IHC) analysis showed positive p53 staining. In addition, IHC analysis at the time of malignant transformation demonstrated positive p16 staining.
Conclusion: In benign epidermoid cysts, it is considered to cause malignant transformation when squamous metaplasia or p53 mutation is observed. Therefore, strict follow-up is required while paying attention to the characteristic changes in MRI for early detection and timely treatment of malignant transformation.
Keywords: Cerebellopontine angle, Epidermoid cyst, Malignant transformation, p16, p53, Stratified squamous epithelial metaplasia
Intracranial epidermoid cysts are rare congenital neoplasms that are clinically indolent and histologically benign, and account for 0.2–1.8% of all intracranial tumors.[
Here, we report a case of a patient with a cerebellopontine angle (CPA) epidermoid cyst that was determined to be squamous epithelial metaplasia and p53 mutation on histopathology at the first operation. Although the tumor was initially benign, malignant transformation was detected 6 years after the initial operation, with changes on MRI. Characteristics of the cyst that were detected upon the initial immunohistochemical (IHC) analysis were considered to be useful for predicting future malignant transformation. The data of this case before recurrence have already been published in a previous paper.[
History and surgical treatment
A 59-year-old woman presented with no relevant past medical history initially presented in 2012 with a 3-year history of right tinnitus, hearing disturbance, and hemifacial paresis. Her right facial function was House–Brackmann (H-B) Grade III, and hearing function was American Academy of Otolaryngology–Head and Neck Surgery (AAOHNS) class B. MRI displayed an extra-axial mass lesion with a maximum diameter of 20 mm in the right CPA. The lesion showed a low-intensity signal on T1-weighted imaging, a high-intensity signal on T2-weighted imaging, and a high-intensity signal on diffusion-weighted imaging (DWI) [
Magnetic resonance imaging (MRI) and intraoperative findings of a 59-year-old woman with a right cerebellopontine angle epidermoid cyst, before its malignant transformation (a-d) Preoperative MRI displayed a low-intensity signal on T1-weighted imaging, a high-intensity signal on T2-weighted imaging, and a high-intensity signal on diffusion-weighted imaging (DWI) without enhancement on contrast enhanced T1-weighted imaging. (e) The tumor contents (*) were pearly white debris, and the tumor capsule was a translucent thin membrane, most of which could be easily removed from the surrounding tissue. (f) A small portion of the capsule was left because of its tight adhesion to the facial nerve. (g) Postoperative MRI displayed no obvious residual tumor. MRI sequences in (a) is T1-weighted images. MRI sequences in (b) are T2-weighted images. MRI sequences in (c and g) are DWI. MRI sequences in (d) are contrast-enhanced T1-weighted images. C=Tumor capsule; V=Trigeminal nerve; VI=Abducens nerve; VII=Facial nerve; VIII=Vestibulocochlear nerve.
Magnetic resonance imaging (MRI) and intraoperative findings of a 59-year-old woman with a right cerebellopontine angle epidermoid cyst, after its malignant transformation (a-c) MRI 6 years after the initial surgery displayed slight characteristics of recurrence. The lesion showed a low-intensity signal on T1-weighted imaging, a heterogeneous low-intensity signal on T2-weighted imaging, and a low-intensity signal on DWI. (d-i) MRI 8 years after the initial surgery displayed a contrast effect on the tumor capsule, suggesting malignant transformation. (j) The tumor contents (*) were yellowish and flaky debris, unlike that of the initial surgery. (k) The tumor capsule was a thick and cloudy membrane that tightly adhered to the surrounding cranial nerves and brainstem. MRI sequences in (a and d) are T1-weighted images. MRI sequences in (b and e-g) are T2-weighted images. MRI sequences in (c) and (h) are DWI. MRI sequences in (i) is contrast-enhanced T1-weighted images. C=Tumor capsule; VII=Facial nerve; VIII=Vestibulocochlear nerve.
At the time of the first surgery, histological analysis revealed that the cyst lining was composed of stratified squamous epithelium with a granular layer and abundant lamellated keratin flakes. The histological diagnosis was an epidermoid cyst. The cyst lining demonstrated multilayered squamous metaplasia owing to the proliferation of basal cells with mild nuclear atypia [
At the time of the second surgery, histological analysis revealed that the cyst lining had typical epidermoid features, and in many parts the cyst lining showed multilayered squamous metaplasia with atypical features, such as the loss of cellular polarity and few mitotic figures [
Histopathological findings of the tumors removed at the first (a-d) and second (e-h) surgeries (a) Hematoxylin and eosin staining showing a cyst with a lining composed of stratified squamous epithelium with a granular layer and abundant lamellated keratin flakes. The squamous epithelium shows multilayered squamous metaplasia in some regions, resulting from the proliferation of basal cells. These squamous cells show mild atypical features and loss of cell polarity (original magnification: ×200). (b-d) Immunohistochemical analysis (b: Epithelial membrane antigen (EMA), ×200; c: p53, ×200; d: p16, ×400). The stratified squamous epithelial cells show partial positive staining for EMA, and 70% to 80% of the cells were positive for p53 and 10% to 20% of the cells were positive for p16. (e and f) Hematoxylin and eosin staining showing the cyst lining composed of stratified squamous epithelium with a granular layer and abundant lamellated keratin flakes. (e) In many parts of the cyst lining, the squamous epithelium shows multilayered metaplasia of atypical squamous cells, with a few mitotic figures (e and f: original magnification ×200) (g and h) Immunohistochemical analysis (g: p53, ×200; h: p16, ×200). Almost all atypical squamous cells were positive for p53, and 30–40% of the cells were positive for p16.
Intracranial epidermoid cysts are congenital lesions caused by ectodermal cell migration during neural tube closure, at 3–5 weeks of gestation.[
Imaging findings that are suggestive of the malignant transformation of a benign intracranial epidermoid cyst is the appearance of rapid growth, peritumoral edema, tissue invasion, low-intensity signal on DWI, and the appearance of new enhancement following contrast administration[
At the time of reoperation, the tumor capsule was tightly adhered to the surrounding tissue, so the removal rate was lower than that at the first surgery. However, this finding is not specific to malignant transformation because the tumor capsule becomes more difficult to remove also during the reoperation of benign epidermoid cysts.[
Regarding postoperative adjuvant therapy for the malignant epidermoid cysts, as a review by Kwon et al.[
The difference from the pathological findings of a typical benign epidermoid cyst at the time of initial surgery in our patient was that multilayered squamous metaplasia caused by the proliferation of basal cells with mild nuclear atypia, and loss of cellular polarity without mitotic figures were observed. In a previous report, Bayindir et al.[
Although epidermoid cysts are benign, it is considered to cause malignant transformation when squamous metaplasia or p53 mutation is observed. Therefore, in such cases, strict follow-up is required while paying attention to the characteristic changes in MRI for early detection and timely treatment of malignant transformation.
The authors certify that they have obtained all appropriate patient consent.
There are no conflicts of interest.
The authors are indebted to Helena Akiko Popiel, Department of International Medical Communications of Tokyo Medical University for her review of the English manuscript. And we thank Ms. Eriko Hikawa for her assistance in preparing this manuscript.
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