Teaching Case

A 6-year-old girl presented with a mild numbness and headache on the left side of her face. Her symptoms had gradually increased since she was 3 years old. During neurological examination a mild paresthesia was diagnosed at the innervation area of the ophthalmic nerve [V1] and the maxillary nerve [V2].

On her 3-year-old MRI there was a well-defined lobulated mass with a size of 7 x 8 mm in the left Meckel’s cave. The mass was hyperintense on T1-W and isointense on T2-W compared to CSF and had diffusion restriction on DWI (Fig. 1). A new non-contrast brain MRI was planned. On new MRI, the mass grew up to 15x12 mm and it enlarged the left Meckel’s cave. The features of the tumour remained the same on T1-W, T2-W, FLAIR images and DWI (Fig. 2). Surgical operation was rejected by the patient’s family and they chose to be followed-up. Medication for the patient’s symptoms was recommended.

Intracranial epidermoid tumours are very well-defined lobulated masses which are isodense or mildly hyperdense compared to CSF on CT and usually isointense on T1-W images and T2-W images or slightly hyperintense on T2-W images compared to CSF on MRI [1]. They often have heterogeneous signal intensity which is higher than CSF on FLAIR sequences. They do not show enhancement on contrast-enhanced images on both CT and MRI. The densities and intensities may show different characteristics due to the content of the tumour. Cholesterol and keratin components account for their typical imaging characteristics on DWI. On DWI they show diffusion restriction which distinguishes it from the other cystic masses (e.g. arachnoid cyst, dermoid cyst, inflammatory cysts or neurenteric cyst) [1, 2]. An arachnoid cyst is a well-circumscribed CSF collection which has the same signal intensity as CSF on all sequences. Epidermoid tumours differ from dermoid cysts which have fat signal due to sebum content. Inflammatory cysts, e.g. neurocysticercosis, may show peripheral contrast enhancement with oedema. Neuroenteric cysts do not show contrast enhancement or diffusion restriction [1]. As the epidermoid tumour is slow-growing, patients have often no symptoms. Thus follow-up would be a good approach. Surgical excision is the treatment option if the tumour is symptomatic [2-5]. However, complete resection may be impossible when the tumour invades the adjacent cranial nerves or vessels. Recurrence rate is high when it is not totally resected [6-9]. Meckel’s cave is a very rare localization for epidermoid tumours. Few cases are discussed in the literature with CT and/or MRI findings [2-9]. The tumours were located in the left or right Meckel’s cave. The patients were between 25 and 61 years old with a female predilection. They had trigeminal [V.] nerve palsy and also extension or mass effect to the adjacent structures due to the tumour. Some had oculomotor [III.], abducens [VI.], facial [VII.] and vestibulocochlear [VIII.] nerve palsies [2, 4, 5]. After the radical surgical removal, patients were relieved of symptoms without any complication [2-9].

In conclusion intracranial epidermoid tumours should be considered in the differential diagnosis of cranial neuropathies and headache in children. Brain MRI with DWI should be used in order to show the imaging characteristics of the epidermoid tumours in rare locations like Meckel’s cave.