Epidermoid cysts or tumors were first described by Cruveilhier[11
] and designated the most beautiful tumors of the body by Dandy.[12
] Although the formation of epidermoid lesions is caused during the 3rd
week of gestation by incomplete cleavage of the neural tissue from the cutaneous ectoderm, the mecchanical introduction of such skin elements can also occur later in life by any mode of skin puncture.[13
] Epidermoid cysts have been reported as sequelae of trauma and surgery in bone, cartilage, and abdominal organs.[14
] The formation of epidermoid cysts after lumbar puncture has also been documented, most commonly in neonates, although at least three reports document their occurrence in adult patients.[16
] In the literature, three previous reports indicated the intracranial development of epidermoid cysts after head trauma or surgery.[18
] Epidermoid cysts have a thin capsule of stratified, keratinized squamous epithelium.[21
] They grow linearly as a result of desquamation of epithelial cells, which later break down into keratin a cholesterol. However, they may also expand and become enormous by neoplastic cellular growth. Estimates of the incidence of epidermoid cysts have ranged from 0% to 8% of all expansive intracranial lesions.[1
] The cisterns of the CPA and parasellar region are the most common site for development of an epidermoid cyst.[1
] On CT scanning, these lesions generally appear as well-defined lobulated hypodense masses, and occasionally display calcification in the cyst wall. On MR imaging, epidermoid cysts typically show low signal intensity on T1-weighted images and high intensity on T2-weighted images. Diffusion-weighted (DW) MR imaging has been found to be helpful in the differential diagnosis from arachnoid cysts, inflammatory cystic lesions, and dermoids.
The symptomatic onset in epidermoid cysts is usually slow, lasting 2 or more years, with headache as the most common symptom. Although, some patients with remitting signs and symptoms[27
] or with rapid onset[6
] have been reported. Epidermoid cysts of the CPA cause the symptoms and signs of a slowly expanding mass in that region,[30
] including ataxia, nystagmus, facial pain, paresthesias, and weakness.[23
Our case has unusual features such as: epithelial cell implantation into the cranium by penetrating injury, the location of the cyst, the concomitant presence of an adjacent cerebellar abscess, and the long delay to clinical presentation. Although, unusual CT and MRI appearance of intracranial epidermoid cysts has been described, hyperintensity in the CT without hemorrhage and the heterogeneously hyperintense appearance on both T1 and T2 weighted imaging and no contrast enhancement on both sequences seen in our case are interesting features. We speculate leakage of the irritant cyst content and resultant formation of granulation tissues inside and in the wall of the cyst as the cause for unusual radiological presentation. The penetrating trauma of the external auditory canal 20 years ago as an underlying cause for both lesions makes this case unique.
In conclusion, implantation of skin causing epidermoid cyst is well known in the lumbar area, after repeated lumbar punctures with the use of stylet. Severe head and spinal trauma were postulated as a causative factor for the formation of intracranial epidermoid cysts. To our knowledge, this is the first documented case of an implantation induced epidermoid cyst and an adjoing brain abcess caused by a small penetrating trauma through the external auditory canal. We postulate that due to persistant fistula, there was secondary infection and cerebellar abscesses. The appropriate treatment consisted of complete removal of the epidermoid cyst and cerebellar abscesses followed by vascularized reconstruction of the infected site and the fistulous tract, which allowed healing and excellent outcome of the patient.