Patient Spectrum

We searched the database of the department of neurosurgery, at a tertiary care referral center, for all cases of intracranial epidermoid cysts operated between January 2005 and January 2020. Details of surgical intervention and subsequent follow-up were extracted from our meticulous record keeping system.

Inclusion Criteria

1. Purely intraparenchymal epidermoid with no evidence of extension in the cisternal spaces.

2. Histologically proven primary IEC.

Exclusion Criteria

1. Recurrent or residual lesions

2. Intraparenchymal inclusion cysts other than epidermoid.

Five patients were identified to have purely intraparenchymal supratentorial epidermoid cyst. The preoperative magnetic resonance imaging (MRI), clinical findings, postoperative course, and follow-up details were retrieved from clinical record keeping system. The operative findings were noted from the hospital information system (HIS). Recent follow-up was done telephonically.

Literature Review

For literature review, the Medline database was searched through the PubMed. The search query entered was (“intraparenchymal”[All Fields] OR “intracerebral”[All Fields] OR “intraaxial”[All Fields]) AND ((((epidermoid cyst) OR (cholesteatoma)) OR (pearly tumor)) OR (“Epidermal Cyst”[Mesh])). Google Scholar was also searched with same keywords. Duplicate articles were removed. Articles published in English, with full-text available and having adequate information were included for further analysis.

Statistical Methods

Statistical analysis was done using Statistical Package for the Social Sciences (SPSS) version 22.00 (IBM, New York, United States). The parametric data were expressed as mean/median and nonparametric data were expressed as number (n) and percentage.

Clinical Presentation

The present series and the review of literature suggest that men are affected more than women by supratentorial IEC (M:F= 1.6:1). Most of these patients are of young or middle age and present with seizures as the most common complaint. Headache is also a common presenting complaint. Other symptoms include focal neurological deficits, meningitis, altered sensorium, and lobar signs such as disinhibition, personality changes, distractibility, etc. Zheng et al in their series of six patients had four patients in supratentorial compartment.24 There were equal males and females, and headache was the most common presenting complaint. Some patients can present acutely with feature of raised ICP following increased perilesional edema or hemorrhage (Fig. 4).7 10 11 23 We found frontal lobe to be the most common site of supratentorial IEC (54.1%). The other sites included temporal lobe, parietal lobe, and thalamus. Cases of IEC involving corpus callosum, pineal gland, and occipital lobe have been also reported.14 Most of these reports are from Japan. Kaido et al reported temporal lobe as the most common site of IEC in the Brain Tumor Registry of Japan and in their literature review.14 These features are significantly different from the more common cisternal epidermoid cysts. They present most commonly in cerebellopontine cistern (60% of all epidermoid cysts) with headache or multiple cranial nerve palsy.

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Fig. 4 The magnetic resonance imaging of the patient (35). Patient had presented with raised intracranial pressure headache and progressive hemiparesis. (A) The tumor is hypodense on plain computed tomography of the head involving the right frontal lobe. Specks of hyperdensity is seen with the tumor. It is compressing the ipsilateral lateral ventricle. (B) Tumor is hypointense on T1 axial image with tiny specks of hyperintensity within. (C) The tumor is homogenously hyperintense in T2- weighted images. The compression and flattening of gyri is appreciated. (D) There is no contrast enhancement seen on T1 + contrast image. (E) It is isointense on apparent diffusion coefficient sequence and (F) hyperintense on the diffusion-weighted imaging sequence. These findings are suggestive of intraparenchymal epidermoid cyst with possible small hemorrhages (late subacute). No attachment to the falx was noted intraoperatively.

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Fig. 4 The magnetic resonance imaging of the patient (35). Patient had presented with raised intracranial pressure headache and progressive hemiparesis. (A) The tumor is hypodense on plain computed tomography of the head involving the right frontal lobe. Specks of hyperdensity is seen with the tumor. It is compressing the ipsilateral lateral ventricle. (B) Tumor is hypointense on T1 axial image with tiny specks of hyperintensity within. (C) The tumor is homogenously hyperintense in T2- weighted images. The compression and flattening of gyri is appreciated. (D) There is no contrast enhancement seen on T1 + contrast image. (E) It is isointense on apparent diffusion coefficient sequence and (F) hyperintense on the diffusion-weighted imaging sequence. These findings are suggestive of intraparenchymal epidermoid cyst with possible small hemorrhages (late subacute). No attachment to the falx was noted intraoperatively.

Radiological Features

The contents of ruptured cysts produce local inflammation. There is development of surrounding gliosis and granulation tissue formation that accounts for hemorrhage and peripheral contrast enhancement.10 27 28 Irrespective of other MRI sequences, the hyperintense signal on DWI is diagnostic of IEC and also recommended for assessing extent of excision postoperatively. The DWI contrast depends on the apparent diffusion coefficient (ADC) value and the proton density. IEC has a low ADC due to the cystic nature of the tumor along with remarkable T2 prolongation causing T2 shine through effect. The histopathological finding responsible for the hyperintense signal on DWI is the presence of abundant keratin debris filled in the lumen of the cyst. The restriction of water diffusion is due to the concentric layers of keratin filaments within the cyst, thus limiting the movement of water molecules to planes formed between the layers of keratin.29 However, sometimes there may be hypointense signal on DWI.17 21

An absence of contrast enhancement is not a reliable diagnostic criterion for IEC as 37.9% cases showed some enhancement. However, the pattern was always peripheral. Contrast enhancement has been reported in 35% of epidermoid cysts which is comparable to IEC.30 The cisternal and IEC share similar MRI findings. Peritumoral edema and calcification may also be present in few cases.4 10 14 15 20 Few cases of “white epidermoid cysts” has also been reported. These cysts are T1 hyperintense due to predominant lipid content.8 21 Such atypical MRI features are common in IECs.17 It is commonly misdiagnosed as ganglioglioma (in presence of calcification) or cerebral abscess (in presence of thin peripheral enhancement) based on preoperative MRI findings.

Surgical Features

Most of the patients undergoing surgery had complete excision of the lesion. The tumor was well capsulated and had good plane in the form of well-defined tumor–brain interface with gliotic changes in the adjacent brain parenchyma, facilitating complete tumor excision. There is a thin layer of gliotic brain parenchyma, with variable thickness, surrounding the tumor which helps in demarcating the lesion.5 19 However, most of them had some degree of adhesion requiring careful dissection during surgery. Intraoperative spillage can be prevented by using large cotton patties spread around the site of tumor excision. Tumor can be visualized after a small corticectomy. Further steps of tumor decompression must be performed under high magnification of surgical microscope with copious irrigation of saline over the operative field. In majority of the cases, the tumor gets delivered with small-to-moderate-sized corticectomy on performing sequential decompression followed by dissection, with identification of the tumor–brain interface all around. There is available literature supporting the adherence of the dura mater to the underlying tumor.5 11 20 Intraoperative monitoring is usually not required as the anatomical landmarks are well preserved and tumor–brain interface is well defined. Because of their extremely slow growth, these tumors tend to push the adjacent brain parenchyma along with the eloquent cortex rather than infiltrating/encasing the neural structures such as the cisternal epidermoid cyst. This leads to a significant amount of disparity between the actual location of the eloquent regions and their expected location based on the craniometric points. The clinical symptoms are mostly due to the local irritation or the compression by the tumor on the adjacent brain parenchyma. de Macêdo Filho et al reported a case of IEC near Broca’s area. The tumor could be completely excised under awake craniotomy.18 These symptoms tend to gradually resolve completely following surgery.10 14 19 However, aggressive resection of adherent capsule on the eloquent area may injure it leading to permanent deficit. Few authors recommend safe decompression as goal of surgery in eloquent zones.5 13 Most of the authors reported a yellowish tint to the tumor. This could be suggestive of chronic microhemorrhages around the tumor.14 Adequate intraoperative saline wash and steroid cover may prevent postoperative aseptic meningitis and hydrocephalus. Some authors recommend irrigation of surgical field with hydrocortisone.31 We had not used it in any of our cases. Chemical meningitis was not reported in any of the cases. Eight mg IV dexamethasone before induction and 4 mg IV dexamethasone TDS (three times daily) for 3 days postoperatively were given in all these cases. Intraoperative spillage of cyst content must be minimized. Unlike the cisternal cysts that are associated with chemical meningitis, we found both in our experience and on literature review that its incidence is less frequently reported with IEC. This is possibly due to less chances of spillage of cyst contents within the subarachnoid space in parenchymal cysts.

Clinical Course and Outcome

Adequate dose of AED in preoperative period and continuation in immediate postoperative period is helpful in preventing any seizure episodes. Most of the patients recover uneventfully. The possible postoperative complications include hemorrhage, aseptic meningitis, and wound-associated complications. Recurrence is common if subtotal excision was performed. However, there exist long duration of symptom free period postexcision before patient develop symptoms due to recurrence. The seizure outcome is good with most patients attaining seizure freedom.5 17 20

Supratentorial versus Infratentorial IEC

These two subgroups differ significantly by virtue of their location. The infratentorial locations include the brain stem and the cerebellum. All the reported cases of pediatric infratentorial IEC are in brain stem. More females were affected than males.24 These tumors present with hemiparesis, seventh nerve palsy, sixth nerve palsy, and gait ataxia.32 The radiological features of these two groups are comparable. As against supratentorial IEC, the principle of surgery in brain stem IEC is safe decompression. Most authors reported adverse outcome with aggressive resection.33 34 Mortality has been reported in three cases of brain stem IEC against only one in supratentorial IEC. Overall, supra- and infratentorial IECs are distinct clinical entities requiring different approach for management.

Limitations

This is a retrospective study. Given the small sample size, the results of this study cannot be generalized. However, being a subset of a rare pathology, a larger sample size is less feasible. Meticulous archival of surgical findings in HIS for record keeping was helpful in avoiding recall bias. Further reporting of such cases would benefit in better understanding this uncommon neurosurgical entity.