Abstract
Intracranial epidermoid cyst (EC) is a slow-growing, benign lesion that rarely undergoes a malignant transformation. When it does occur, the clinical course is aggressive. Certain radiological criteria may give a clue to diagnosis and help in deciding the appropriate course of action as well as prognostication. Surgical excision along with adjuvant radiotherapy is the treatment of choice; however, the overall prognosis is poor as complete excision is seldom possible. We present a rare case of malignant transformation of an intracranial EC without previous history of surgery. Subtotal excision of the lesion was possible, with post-operative histopathological examination revealing squamous cell carcinoma. The patient was discharged from the hospital with no fresh deficits. She was, however, re-admitted on day 36 with features of raised intracranial pressure, for which she underwent cerebrospinal fluid diversion. She underwent intensity-modulated radiation therapy later on.
Keywords: Intracranial epidermoid cyst, Malignant transformation, Complete resection
Introduction
Malignant transformation of an epidermoid cyst (EC) is a rare entity. It mostly develops in patients with incomplete resection of a benign EC but may also arise de novo. Certain clinical and imaging findings may help to clinch the diagnosis pre-operatively, but it requires a strong clinical suspicion. Complete surgical excision is the treatment of choice, which is rarely achieved due to its propensity to invade surrounding structures. As a result, the overall prognosis remains grim. We present this report on a case of malignant transformation of an EC that we encountered at our institute and share our experience managing it.
Case report
A 52 years old female patient, with a known case of type II diabetes mellitus (DM), hypertension, and coronary artery disease (CAD), presented with complaints of gait instability and paresthesias on the left side of the body of one-month duration. She subsequently developed features of raised intracranial pressure (ICP). Neurological examination revealed spastic hypertonia in left upper limb with no motor deficit, no cranial nerve deficits, no parinaud's syndrome, and no papilledema on fundus examination. She had an ataxic gait and no obvious cerebellar signs. She underwent contrast-enhanced magnetic resonance imaging (CEMRI) brain with magnetic resonance spectroscopy (MRS) at our institute (Fig. 1, Fig. 2).
Fig. 1.
2.4 × 2.2 × 3.2 cm lesion with an intrinsic component (black arrow) and an exophytic component (white arrow) in the Rt ambient cistern extending to quadrigeminal cistern.
Fig. 2.
The intrinsic component shows heterogenous post-contrast enhancement (white arrow), and the exophytic component shows restriction of diffusion (black arrow).
On MRS, the lesion showed lipid and lactate peaks and a mild choline peak. Based on these findings, the following differential diagnosis of EC with malignant transformation, high-grade glioma, and tuberculoma with abscess was considered.
She underwent a right occipital transtentorial approach with excision of tumor with the prior placement of an external ventricular drain (EVD). The exophytic component was pearly white, soft in consistency, with a well-defined brain–tumor interface in most parts.
However, this lesion seemed to be invading into the midbrain on the dorsal aspect. The cisternal component was completely removed. No clear plane was available between invasive component and midbrain; hence, the decision to only get tissue for biopsy was taken to prevent post-operative deficits (Fig. 3).
Fig. 3.
Histopathological analysis revealed predominantly lamellated keratin flakes along with a small tissue bit lined by stratified squamous epithelium. The rest of the tissue showed an invasive tumor arranged in clusters with individual cells showing marked nuclear pleomorphism and high N:C ratio.
Post-operative CEMRI brain revealed complete excision of the exophytic component with resolution of hydrocephalus and residual intrinsic part of the lesion (Fig. 4). A thorough evaluation was done to rule out metastasis from a squamous cell carcinoma elsewhere. However, no lesion was found on endoscopic ENT examination, gynecological examination, and whole body positron emission tomography (PET) scan. The final diagnosis of malignant EC was made, and the patient was referred for adjuvant radiotherapy. Patient consent was obtained for use of images in the study.
Fig. 4.
Post-operative MRI showing residual intrinsic component.
Discussion
Epidermoids are benign, slow-growing lesions that account for around 1% of intracranial tumors.1,2 The growth rate is similar to the epidermal cells of the skin.3 The most common intracranial site is in the cerebellopontine angle (CPA) (40%) followed by the suprasellar cistern (18%), less commonly present in Sylvian fissure, cerebral and cerebellar hemispheres, and ventricles.4 It is rare to find ECs in the brainstem, with purely intrinsic ones being the rarest.3 In our case, the EC had an intrinsic as well as extrinsic component.
ECs develop from ectodermal squamous cell remnants.5 The ectodermal components get trapped, traveling along the otic vesicles, during neural tube closure in the third to fifth weeks of embryonic life, which accounts for the most common location being the CPA.2, 3, 4 These cysts are lined with benign keratinizing squamous epithelium and contain laminated keratin and cholesterol in a solid crystalline state, which forms a cheesy, flaky, and soft putty-like material.1,3,4,6 They are most commonly detected in the third or fourth decade of life and have a higher incidence in males.4
Malignant transformation of an EC is a rare occurrence.1,7 Garcia et al defined the criteria for malignant transformation of ECs; (1) tumor has to be restricted to the intracranial, intradural compartment without invasion of or extension beyond the dura or cranial bones. (2) There must be no extension or invasion through intracranial orifices. (3) There must be no communication or connection with the middle ear, air sinuses, or sella turcica. (4) There must be no evidence of nasopharyngeal tumor.8 Hamlat et al added two additional criteria; (1) there should be the presence of a benign squamous cell epithelium within the malignant tumor, and (2) metastasis of carcinoma should be excluded.9 Malignant transformation of intracranial epithelial cysts has been classified into five groups; (1) initial malignant transformation of an EC, (2) malignant transformation from a remnant EC, (3) malignant transformation with leptomeningeal carcinomatosis, (4) squamous cell carcinoma from other benign cysts, and (5) other malignancies arising from the benign cysts.9 According to these criteria, our case is an initial malignant transformation of an EC. The underlying mechanisms causing malignant transformation are not well known. Explanations put forward include chronic inflammation with cyst rupture, subtotal resection of the cyst, and introduction of a foreign material intra-operatively or a de-novo malignant change in the epithelial lining of the EC.5,6
Malignant transformation should be considered in patients with rapid progression of symptoms like irritation of cranial nerves or compression of surrounding neural structures.1 On imaging, it is often difficult to differentiate between the malignant transformation of EC and gliomas.1 These lesions show pronounced peripheral enhancement with cystic appearance on MRI. Leptomeningeal enhancement may be observed when there is leakage of cyst contents into the subarachnoid space resulting in chemical meningitis.1 Malignant ECs may not show restricted diffusion on DWI sequences, which may cause difficulty in pre-operative diagnosis7.1.
The treatment of choice for malignant ECs is complete excision along with the complete removal of the capsule followed by radiotherapy.7,10 However, a complete removal is seldom possible because the tumor firmly adheres to surrounding neurovascular structures and surgery.6 Tamura et al suggested that Gamma Knife Radiosurgery (GKRS), when used as adjuvant radiotherapy, appears to offer the best survival benefits for patients with intracranial squamous cell carcinomas.10 Despite treatment, the prognosis of malignant transformation of an EC is poor; the mortality rate may be as high as 75%.1,7
We recommend complete excision of these lesions, whenever possible, followed by adjuvant radiotherapy.
Patients/ Guardians/ Participants consent
Patients informed consent was obtained.
Ethical clearance
Not Applicable.
Source of support
Nil.
Disclosure of competing interest
The authors have none to declare.
Acknowledgements
None.
References
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