Intradiploic Pterional Epidermoid Tumor: A Case Report and Review of literature.

Intradiploic epidermoid cyst is an uncommonly occurring neoplasm, and only about 200 cases are reported in the form of isolated case report. It is presumed to occur due to ectodermal cells in inclusion in the bone tissue during embryonic life neural tube closure. It commonly remains asymptomatic or rarely presents as a bony lump in the skull bone. Authors report present an interesting case, which presented with swelling, and underwent successful surgical resection. Pertinent literature along with diagnosis and management is briefly reviewed. These lesions can erode the bone and involve the brain parenchyma due to their proximity to the brain. Radiological imaging is very helpful in accurate diagnosis of these lesions and in differentiating intradural from intradiploic varieties of epidermoid. We present an unusual case of this pathology.

INTRODUCTION

Intracranial epidermoid tumors are congenital tumors of benign nature containing epithelial cell remnants, rich in cholesterol.[1] They account for approximately 0.2%–1.8% of all intracranial tumors. Cushing was credited to describe first radiologic feature of intradiploic epidermoid as focal areas of osteolysis and presenting typically sclerotic smooth margin.[2] Usually, intracranial epidermoid tumors are located intradurally and but rarely occur in the intradiploic space of frontal, temporal, and occipital bones in the skull.[3] They may remain asymptomatic or cause a focal mass, or may erode into dura and rupture into subarachnoid space leading to development of chronic aseptic meningitis.[4] Preoperative diagnosis presents a diagnostic challenge and helps in proper surgical planning; however, many times it is difficult to diagnose on neuroimaging in the preoperative phase. However, current development in magnetic resonance imaging sequences can obviate this problem to an great extent. Authors report an interesting case of intradiploic epidermoid, who was managed successfully.

CASE REPORT

A 4-year-old female patient presented herself to the outpatient unit of the neurosurgery department with a mass on the lateral border of the left orbit. On examination, the patient had no neurological deficit. Brain computed tomography (CT) scan was performed which showed an intradiploic cyst lesion in left side pterional region [Figure 1]. The patient was submitted to surgery and excision of the cystic lesion was performed. The pathology report was compatible with intradiploid epidermoid cyst. The patient presented satisfactory evolution without recurrence of lesions at 6 months of follow-up.

Figure 1

Computed tomography scan showing a intradiploic pterional epidermoid

DISCUSSION

Epidermoid is benign development lesion representing inclusion cysts of ectodermal origin. The cyst is formed of desquamated epithelial cells in concentric layers, and solid crystalline cholesterol and keratin granules. It can involve any part of craniospinal neural axis; however, about 90% of intracranial epidermoids are located being intradural and rest 10% are located exrtradurally.[5] Usual distribution in descending orders of frequencies includes located at the cerebellopontine angle, at the fourth ventricle and middle cranial fossa. The pathomechanism involve faulty cleavage of the neural from the cutaneous ectoderm in the neural groove during of neural tube closure phase, associated with inclusion of ectodermal cells, during intrauterine life.[6]

The intradiploic epidermoid tumors usually result due to entrapped ectodermal embryonal remnants within the skull bones or rarely secondary to trauma. Epidermoid cyst tumor is commonly present with long-standing painless scalp at which may remain static or have slower growth and presenting after rupture to exterior following trauma or intradural after eroding inner table of skull and dura producing aseptic meningitis. The intradiploic epidermoid may present with headache and focal seizures more frequently; cranial nerve deficits or extremely rarely raised intracranial pressure. Symptoms due to mass effect are seen less commonly.[7]

The preoperative diagnosis poses a diagnostic challenge and incomplete removal predisposes the risks of recurrence, inflammation, and possibility of malignant transformation. Imaging is essential before any surgical intervention. Further, imaging helps in postoperative follow-up of these tumors as a recurrence rate of 0.3%–0.25% reported after incomplete excision of epidermoid. X-ray skull shows presence of an expansile, lytic lesion with well-defined sclerotic borders, intradiploic epidermoid causes expansion of both inner and outer tables of the skull, and erosion of both inner and outer tables of skull observed in 46% cases and 36% cases has isolated outer table involvement.[7] The sclerotic borders are characteristic of benign lesions such as epidermoid cyst and typically lacking in eosinophilic granuloma due to their aggressive and malignant nature.[7] CT allows better assessment of both bony involvement as well intracranial extensions extent of involvement of the inner and outer tables, presence of table destruction and of calcification, the nature and density of the intradiploic epidermoid cyst with the sclerotic skull margins.[891011] Intradiploic epidermoid tumors needs to differentiate from dermoid cysts, cholesterol granuloma, eosinophilic granuloma, and calvarial hemangioma, and osseous tumors such as aneurysmal bone cysts, fibrous dysplasia, and eosinophilic granuloma as these are also presents with expansile lytic lesions in young adults and children.[9101112] Rupture, bleeding, and chronic aseptic meningitis can complicate. The chronic inflammatory meningeal reaction due to their rupture can additionally lead to the development of trigeminal neuralgia and other neurologic deficits. Malignant transformation of epidermoid too has been reported.[10]

Wide complete surgical excision is the treatment of choice with appropriate cranioplasty should be carried out and the patients need regular follow-up. Really, epidermoid can show malignant transformation. Primary intracranial squamous cell carcinoma is extremely rare, with most of the cases arising from malignant transformation of an epidermoid or a dermoid cyst.[13] Agrawal et al. reported a 45-year-old male, who presented with intermittent headache and recent onset of altered sensorium and imaging's revealed a midline posterior fossa mass lesion compressing the fourth ventricle and causing hydrocephalus underwent surgical excision and histopathology was squamous cell carcinoma possibly arising.[13]

CONCLUSION

Epidermoid tumors located in the intradiploic space are beningn lesions, having slow growth rate and complete surgical management can provide good long-term outcome. Intradiploic epidermoid tumors should be considered as one of differential diagnosis of all the intradiploic calvarial mass.

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Conflicts of interest

There are no conflicts of interest.