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|Year : 2018 | Volume
| Issue : 3 | Page : 763-766
Melanotic intracranial epidermoid: Case report and description of a new subtype
Krishnamurthy Sridhar1, Mukul Vij2
1 Department of Neurosurgery, Gleneagles Global Health City, Institute of Neurosciences and Spinal Disorders, Chennai, Tamil Nadu, India
2 Department of Pathology, Gleneagles Global Health City, Institute of Neurosciences and Spinal Disorders, Chennai, Tamil Nadu, India
|Date of Web Publication||15-May-2018|
Dr. Krishnamurthy Sridhar
Department of Neurosurgery, Institute of Neurosciences and Spinal Disorders, Gleneagles Global Health City, 439, Cheran Nagar, Perumbakkam, Chennai - 600 100, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Intracranial epidermoids are generally seen as hypodense nonenhancing lesions on computed tomography scans; and, as T1 hypointense and T2 hyperintense lesions on magnetic resonance imaging (MRI). Unusual radiological findings have been reported earlier. The authors present the case of a 54-year old male patient who had prior intracranial surgery. On MRI, there was a thick peripheral mantle of diffusion restriction with a central core of brilliant T1 hyperintensity and very black T2 hypointensity. The peripheral mantle showing diffusion restriction was heterogeneously T1 hypointense and T2 hyperintense. At surgery, there was a typical pearly white epidermoid peripherally with a greenish-brown centre. Pathology showed abundant extracellular melanin which was also found in the basal layer. The authors present the first case of a melanin pigmented intracranial epidermoid in literature, describing a new histological subtype.
Keywords: Epidermoid, melanocyte, melanotic, pigmented
Epidermoid tumors may present with unusual radiological findings including hyperdensity on the CT scan and a T1-weighted hyperintensity. One rare cause of this finding is melanin pigmentation of the tumor, which has not been described earlier in literature.
|How to cite this article:|
Sridhar K, Vij M. Melanotic intracranial epidermoid: Case report and description of a new subtype. Neurol India 2018;66:763-6
Epidermoids typically present as hypodense nonenhancing lesions on the computed tomography (CT) scan, and as T1 hypointense and T2 hyperintense lesions on magnetic resonance imaging (MRI).,,, While lesions with unusual radiological characteristics have been reported in the literature, these have been mostly attributed to a high protein content, or the presence of hemorrhage, and/or inflammation.,,, Although the presence of melanin in the basal layers of the cutaneous epidermoids has been demonstrated, a pigmented epidermoid cyst with melanin pigment within it, is a rare finding even in the skin and oral cavity. Massive melanin deposition in an intracranial epidermoid causing tumor pigmentation has not been reported till date. The authors present the first case in the literature of an epidermoid tumor in the posterior fossa with unusual radiological characteristics due to massive melanin pigmentation of the tumor and describe a new histological subtype of the tumor.
| » Case History|| |
A 54-year old male patient presented with a 6-month history of worsening imbalance and swaying while walking, with a month's history of hoarseness of voice and hearing loss in the right ear. There was no history of headache, vomiting, seizures, or other signs of raised intracranial pressure. He provided a history of a surgery done more than 20 years ago, for a tumor in the posterior fossa. The details of the surgery were not available nor did the patient know what was done for him. On examination, he was fully conscious and alert with normal higher intellectual functions. The extraocular movements were normal. He had normal trigeminal and facial functions. He had a sensorineural deafness on the right side. There was a minimal deviation of the uvula towards the left side with no impairment of the gag reflex. Swallowing was normal with no regurgitation of fluids. There was no lateralizing motor or sensory deficit. He had minimal right-sided appendicular cerebellar signs with gross ataxia. There were surgical scars indicating a right-sided ventriculoperitoneal shunt surgery, as well as a midline suboccipital cranial surgery.
Noncontrast CT scan of the brain showed evidence of a midline suboccipital craniectomy [Figure 1]. There was a predominantly hyperdense, midline, noncircumscribed lesion with ill-defined borders. There was an isodense peripheral region within the lesion traversing laterally to the right, which seemed to be extending in the higher cuts to the right cerebellopontine angle and the quadrigeminal cistern, with enlargement of the cisterns. The fourth ventricle appeared as a slit that was compressed and pushed anteriorly and to the left. On MRI [Figure 2], the lesion was involving the vermis, adjacent medial aspects of bilateral cerebellar hemispheres, left middle cerebellar peduncle, projecting into the IV th ventricle, and extending into the right cerebellopontine angle through the widened foramen of Luschka. Superiorly, the lesion was extending through the incisura of the tentorium into the supratentorial compartment. The lesion had a thick peripheral mantle of diffusion restriction with a central core of brilliant T1 hyperintensity and very black T2 hypointensity. The peripheral mantle showing diffusion restriction was heterogeneously T1 hypointense and T2 hyperintense. The core remained hypointense on diffusion weighted imaging (DWI). The margins of the core were not smooth but like the blades of saw projecting into the peripheral mantle.
|Figure 1: CT scan brain non-contrast study showing evidence of a previous midline suboccipital craniectomy. There is a hyperdense midline posterior fossa lesion, not well circumscribed, with ill defined margins|
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|Figure 2: MRI of the brain in the (a) FLAIR sequence showing a hypointense midline posterior fossa lesion with irregular margins and a bright hyperintense surrounding area, which extends to the right CP angle; (b) T1 weighted sequence showing a hyperintense centre and a mixed iso- - to hypointense surrounding; (c) Contrast T1 weighted sequence showing no significant enhancement at the centre of the lesion with minimal contrast enhancement at the periphery|
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At surgery, the previous craniectomy site was reopened and was extended towards the right side. After the pseudodura was opened, the cisterna magna was inspected. No lesion was visualized. The inferior vermis was incised to reach the typically white epidermoid tumor. The lesion was firm. Entering the lesion, the tissue within was found to be of greenish brown colour and was soft in consistency [Figure 3]. Almost the entire lesion was of this color and consistency except for the periphery where the lesion was white and flaky. The lesion extended to the cerebellopontine angle, as was seen on radiology, and was entangled with the lower cranial nerves. The lesion was removed near-totally leaving a very thin capsule over the rootlets of the lower cranial nerves and over the middle cerebellar peduncle. There did not seem to be any direct communication of the tumor with the fourth ventricle. Postoperatively, the patient made an uneventful recovery and was discharged on the eighth postoperative day with no new neurological deficits. The pathological examination of the tumor revealed multiple fragments of the cyst, lined with stratified squamous epithelium with a granular layer [Figure 4]. Abundant amounts of luminal acellular orthokeratotic keratin flakes were seen. The cyst wall showed brown pigment containing cells, which were negative for iron stains. The same brown pigment was also seen extracellularly. Melanin was confirmed by Masson Fontana stain and melanin bleach. There was no evidence of malignancy.
|Figure 3: Intraoperative photograph showing the greenish brown intracapsular tumour tissue with the surrounding white epidermoid capsule|
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|Figure 4: Pathological photomicrographs of the patient's tumor. (a) Epidermoid with stratified squamous epithelial lining and keratin flakes (H and E, ×40). (b) Subepithelial connective tissue with abundant brownish melanin pigment in melanophages and mild pigment in basal layers (H and E, ×100). (c) Masson Fontana stain for melanin pigment (×100). (d) Melanin bleach staining (×100, D)|
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| » Discussion|| |
Intracranial epidermoids are most commonly seen in the cerebellopontine angle and the supra- and parasellar regions.,, They are seen as well-defined, hypodense, nonenhancing lesions on CT scans and are commonly hypointense on T1-weighted and hyperintense on T2-weighted MRI scans. There are a number of reports of hyperdense epidermoids on CT scans and epidermoids with unusual MRI characteristics.,, The CT scan finding of hypodensity in epidermoids is based on the cholesterol content of the tumor, whereas the hyperdensity is related to the protein content of cystic lesions, microhemorrhages or prior bleeding into the tumour, inflammation with increased numbers of polymorphonuclear cells, saponification and calcification, and deposition of iron containing pigments. Gupta et al., reported a case of hyperdense epidermoid due to spontaneous hemorrhage within the tumor. The CT scan finding in our patient of a hyperdense lesion without well-circumscribed margins did not suggest an epidermoid tumor on the first look but rather a lesion with either some hemorrhagic component or increased protein content.
On MR scans, most epidermoids have a characteristic appearance. The MR signals in epidermoids are mainly due to the cholesterol and keratin contents of the tumor. Mostly in these tumors, the cholesterol is in the solid state and appears hypointense on T1-weighted scans. Unusual MR findings have been reported.,, Ochi et al., believed that their tumor was hyperintense on the T1-weighted MR image due to the high protein content of the cyst fluid. Bohara et al., reported two cases with unusual MRI findings. One patient had a hyperintense lesion on T1-weighted images, while another had an isointense lesion on T1-weighted images. They concluded that these changes were due to the nonsolid and cheesy consistency of the lesion along with the presence of xanthochromic fluid. Arai et al., while reporting their unusual epidermoid of the Meckel's cave, thought that the tumor was hyperdense on CT scan images and hyperintense on T1-weighted MRI due to the high protein content and viscous nature of the lesion. Spontaneously hyperintense lesions on T1-weighted MR scans include hemorrhagic lesions, protein containing lesions, fatty lesions, calcified or ossified lesions, lesions with other mineral accumulation, melanin containing lesions, and other miscellaneous lesions.
Correlating the CT and MRI findings in our patient, there was a hyperdense lesion seen on CT scan images with a bright T1 hyperintensity and very black T2 hypointensity, raising the possibility of a tumor with subacute bleed. Other possibilities included a high protein content, or fat, or mineral deposition within the lesion. The absence of hypodensity on CT scan images ruled out fat. The presence of subacute bleed, a high protein content, and the deposition of minerals remained in the differential diagnosis. The fact that the patient was operated upon at the same region for a tumor, and had remained asymptomatic for approximately 20 years, suggested that the original lesion was benign. The possibility that the lesion had now changed character remained. In essence, we were looking at a lesion with a low mitotic level which had perhaps changed its character to produce the present CT and MR findings.
On discovering the lesion to be an epidermoid, our thought intraoperatively was that it had turned malignant. We also assumed the color and consistency of the tumor to be due to hemorrhages within the lesion over the years. Melanin in epidermoids is very rare and known to be present only in extracranial locations. We believe this to be the first case of intracranial epidermoid with massive intratumoral melanin pigmentation to be reported in literature. The source of the melanin and why other intracranial epidermoids do not show this pigmentation are questions yet to be answered.
Several authors have reported extracranial epidermoids, especially the cutaneous ones, with excessive melanin deposition.,, Shet found that 63% of epidermoid cysts showed melanin or melanocytes in the basal layer. However, extensive melanin accumulation within the tumor was seen in only 12.6% of cases. Jayalakshmi et al., did not find extensive melanin pigmentation in the 365 cutaneous epidermoid cysts that they studied over a 2-year period. Melanin and melanocytes are generally present in the basal layer of the epidermis. We should expect to see melanocytes and melanin pigment in the basal layer of epidermoid cysts, but we do not. One of the reasons put forth is that the pigmentation seen in the hematoxylin and eosin stains is probably mistaken for hemosiderin and special stains are not used to demonstrate the melanin. On retrospectively studying ten intracranial epidermoid cysts operated in the previous 2 years at our centre, we were able to see melanocytes and intracellular melanin in the basal epidermal layer in 4 cases [Figure 5]. Melanocytes present in the basal layer of the epidermoid tumor are, therefore, in our opinion, not uncommon. This is something that, as previous authors have mentioned, we do not look for.
|Figure 5: (a) Epidermoid with stratified squamous epithelial lining and keratin flakes (H and E, ×40). (b) Mild pigment in basal layers (H and E, ×100)|
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The reasons why there was such an increased melanin production and its dissemination within the lesion in our patient can merely be speculated. An increased frequency of melanin deposition and melanocyte proliferation has been seen in those patients with a dark skin (when compared to a white population) or due to a chronic irritation of the melanocytes present in the lesion. Excessive melanocyte proliferation with melanin incontinence and its deposition within the tumor could then possibly be attributed to the previous surgery and a resultant inflammatory process, which could in turn have triggered the excessive deposition of melanin in the recurrent tumor. However, why it has not been seen in other recurrent tumors is also not known. This excessive melanocyte proliferation and melanin pigmentation is not an indicator of malignancy, and is completely different from the histological character of a melanoma.
| » Conclusion|| |
The authors present the first case of a melanin pigmented intracranial epidermoid in literature, describing a new histological subtype. Melanin and melanocytes could be normally found in the histology of an epidermoid. Massive melanin deposition within the tumor may present with unusual radiological features, and may present intraoperatively as a pigmented epidermoid. It is important for radiologists, surgeons, and pathologists to be aware of the possibility of these rare findings so that these lesions are not mistaken for more aggressive pathologies.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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