Epidermoid Cysts in the Frontal Lobe – A Case Series

Intracranial epidermoid tumors first described by Bailey[1] and Cushing[2] in the early 1920s, account for nearly 1% of the intracranial tumors.[3-5] Thought to arise from displaced epithelial remnants that remain after the neural tube closure, these tumors are usually congenital; however, acquired lesions are rarely reported.[4, 6] These are usually benign intradural but extracerebral lesions and are rarely found within the substance of the brain. Furthermore, fronto-ethmoidal location of epidermoid is rare. Our review of the Medline and Google Scholar databases revealed 28 reported cases. Here we report two cases of frontal lobe epidermoid tumors with specific emphasis on pre-operative radiological features and operative findings.

Case-1

A thirty-year old male presented in the outpatient clinic with complaints of progressively worsening headaches for the past 5 months. The headaches were mild to moderate in intensity and were worse early in the morning. Headaches improved with over-the-counter analgesics. The headaches were also associated with nausea, retching and behavioral changes (mainly forgetfulness). There was no history of seizures, fever, or visual disturbances. His neurological examination was essentially unremarkable, except that his Mini-Mental State (MMS) examination revealed a score of 23 out of 30. The patient had previously undergone Magnetic Resonance Imaging (MRI), which revealed a mass lesion of about 7.5 x 6.0 x 5.5 cm in dimension, located at the right frontal lobe along the anterior part of falx cerebri. The lesion was producing homogenous hypointense signals on T1-weighted images, while it produced heterogeneous bright signals on T2-weighted images. There was no post-gadolinium enhancement of the lesion [Figure 1]. The above findings were suggestive of an epidermoid cyst. The patient underwent a right frontal craniotomy. After opening the dura, a pearly white mass was found with a well-demarcated interface with cerebral surface. The mass was avascular and was easily excised by a suction catheter. A near-total excision was achieved but the capsular membrane had to be left behind as it was adherent to the surrounding cerebral tissue. Histopathological examination of the excised tissue confirmed the diagnosis of epidermoid cyst with keratinous crystals. The patient’s post-operative recovery was un-eventful and he was discharged on the 7^th post-operative day. On follow-up, the patient claimed a remarkable subjective improvement. His headaches had also resolved. At his 6-month follow-up visit, his MMS examination revealed a score of 26/30.

Case-2

A twenty-year old male presented to our emergency department with generalized tonic clonic seizures associated with loss of consciousness, frothy discharge from mouth and urinary incontinence. There was no history of fever, visual disturbances or trauma. On examination, he was drowsy but arousable with a Glasgow Coma Scale (GCS) of 13/15. There were no other neurological deficits and the systemic examination was within normal limits. As per hospital protocol, he was started on intravenous phenytoin. A careful review of the patient’s history revealed that he had complained of mild headaches, which were relieved by over-the-counter analgesics. Computerized Tomography (CT) scan showed a cystic midline lesion extending into the anterior fronto-basal regions bilaterally. The walls of the lesion were hyperdense on the right side. There was no post-contrast enhancement on the CT scan [Figure-2]. MRI revealed a 4.5 x 2.5 x 3.0 cm lesion, which was hypointense on T1-weighted sequences and hyperintense on T2-weighted sequences. There was no post-contrast enhancement [Figure 3].These features were suggestive of an epidermoid cyst. After 48 hours, the patient was clinically stable and underwent a bifrontal craniotomy. The mass was filled with pearly white material and was easily removed using a suction catheter. Due to the avascular nature of the mass, it was possible to achieve near-total excision, leaving only the adherent membranous lining behind. His post-operative recovery was uneventful. Histopathological examination confirmed the diagnosis of an epidermoid cyst. At 3-month follow up, the patient had no complaints and his seizures were well controlled on a maintenance dose of phenytoin.

Since their initial description, epidermoid cysts have been well studied and the natural history of the disease is well described. These benign tumors of embryonal origin are formed between the 3rd and 5th weeks of embryonic development due to the displaced epithelial remnants that persist after neural tube closure.[7, 8] They are often found where two ectodermal surfaces fuse such as the skin, epidural, intradiploic and epicranial tissue.(9) Within the domain of neurosurgery, they commonly occur in isolation at the cerebellopontine angle (37%), suprasellar region (31%), diploie (16%), rhomboid fossa (11%) and spinal canal (5%),[10] accounting for approximately 1% of all the intracranial tumors.[3-5]  Less common locations include the pineal gland, thalami, septum pellucidum and other intraparenchymal locations. In rare cases, they have been reported in other locations such as the lateral ventricles.[10] Epidermoids are generally slow-growing lesions, remaining asymptomatic for long periods of development. Patients generally present with symptoms between the ages of 20-40 years.[11] The presenting symptoms mainly depend on the location and the mass effect of the lesion rather than the natural disease process.[10] Patients with frontal lobe tumors can present with dementia secondary to obstructive hydrocephalus or the local effect of the tumor.[6] Our first patient presented with a low MMS score, which could be attributable to the local effects of the tumor. The presentation of the second case with seizures is an extremely rare presenting symptom. In fact, we found only two other cases in our review of literature of patients presenting with seizures.[8, 12] The mechanism resulting in seizures is unknown; however, we hypothesize that this maybe attributable to direct cerebral compression by the expanding cyst. MRI appears to be the best modality for radiological evaluation of these tumors. Typically epidermoid tumors are hypointense on T1-weighted and hyperintense on T2-weighted images with long relaxation times. Due to the low vascularity of these tumors, no post-contrast enhancement is noted.  Fluid-Attenuated Inversion Recovery (FLAIR)  sequences help distinguish them from similar-appearing arachnoid cysts, as the former are hyperintense. Diffusion-weighted images further enhance the accuracy of preoperative diagnosis.[12-14]  Calcifications may be seen within these tumors in 10%–25% of cases.[9]  Surgical excision is the mainstay of treatment, and is low-risk due to the avascular nature of the tumor. As seen in our case-series, we were able to debulk most of the tumor by a suction catheter. Surgical planning and extent of resection is based on fundamental neurosurgical principles, where preservation of vital structures is followed by maximal debulking. The capsule of the cyst can be problematic in this case as it may be adherent to vital structures and may need to be left behind. The implications of leaving the cyst wall behind include a recurrence of the mass; however, this may be acceptable due to the benign nature of the disease and the indolent pattern of growth giving the patient a long symptom-free interval. Even with subtotal resection of the mass, a mean symptom-free interval of 8 years has been reported.[15] This period can further be enhanced by aggressive resection of the tumor and its capsule; however, it must be balanced within reasonable limits of acceptable risk for neurological deficits. Although benign in nature, these masses have been shown to undergo malignant change.[16-20] On turning malignant, the course of the disease changes rapidly and severe deterioration is noticed. Malignant transformation can be detected by contrast enhancement of the previously avascular tumor. Hamlat et al. while studying malignant degeneration of the remnant lesion, reported that from the seventeen cases undergoing malignant degeneration, six showed enhancement at the time of the initial CT study,[21] indicating that post-contrast enhancement may warrant more aggressive excisional strategies. When considering complications of surgical excision, Roy et al. while analyzing 28 cases of intracranial epidermoids, reported the unfortunate demise of five patients. Other postoperative complications included chemical meningitis in 7, worsening of cerebellar function in 3 and aggravation of cranial nerve deficits in 2 patients. All of the deficits except for one case of cranial nerve deficits resolved with time.[22] In cases of midline front-basal location, Barnett FC et al. reported continued anosmia and mild neuro-cognitive dysfunction with no new deficits,[6] while in our cases as well as those of Iaconetta et al., the recovery was without any complications.[12]

Intracranial epidermoid tumors are rarely found in the frontal lobes. Surgical resection appears the mainstay of treatment; however, the extent of resection is dictated by the adherence of the tumor capsule to surrounding vital structures. The advantages of aggressive neurosurgical intervention must be weighed against an acceptable risk of neurological outcomes. Due to indolent growth pattern, subtotal resection is also acceptable.

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