The common locations of dermoid cyst are
- Scalp (angle of eye and retro mastoid region)
- Skull bones (intradiploic)
- Intracranial, in suprasellar region and posterior fossa
- Intraspinal mainly intradural and associated with other spine defects.
The dermoid cysts are developmental in origin and arise from the nests of embryonic ectoderm which get buried or trapped under the lines of fusion of the ectodermal folds in the developing embryo.
The nervous system develops from the ectoderm. The cells on the dorsal aspect of the developing embryo thicken to form neural plate or placode along the axis of the embryo. The neural tube bends and closes to from a tube called the neural tube from which the whole of the nervous system develops. The neural tube closes in the dorsal midline first in the cervical region and the closure then extending cranially and caudally so that the anterior neuropore closes at 24 days and posterior neuropore at 28 days. Thus, as the neural tube closes last in the caudal part, that is the lumbo-sacral region, there is more chance that this process may be disturbed and nests of cutaneous tissue may get trapped within the developing tube, giving rise to dermoid cyst.
Hence, lumbo-sacral region is the most common site for the dermoids in the spine.
Also, dermoids are commonly associated with spinal dysraphisms. This is because the same process which gives rise to spinal dysraphisms is responsible for the development of dermoid cysts. The low incidence of dermoid in the cervical region is likely related to the embryological process of neural tube closure, which begins in the area of the neural tube destined to become the lower cervical cord and proceeds rostrally and caudally.
Spinal inclusion cysts are usually intradural, extramedullary in location, the common lesions being neuroenteric cysts, arachnoid cysts, epidermoid and dermoid cysts.
Dermoid cysts usually present themselves in childhood, as a consequence of associated anomalies or by symptoms of cord tethering and mass effects. However, in this case, the patient had no associated developmental anomaly of the spine. Because of the absence of any other congenital anomaly of the spine, the patient presented at a later age after she had developed significant symptoms, particularly in the left side of the body. The decompression of the dermoid cyst was carried out by standard micro neurosurgical technique employed for other intramedullary tumors.
However, it was not possible to remove the capsule of the dermoid completely as it was very much adherent to the cord. Any attempt to remove it totally would have lead to unacceptable damage to the cord; and hence, part of the capsule was left behind.
We could found two such cases[2
] where a dermoid cyst was in the cervical cord and was not associated with any other congenital anomalies of the spine. In other reported cases,[3
] the location of the dermoid cyst and the presence or absence of congenital anomaly of the spine is not clear as they have been published in language other than English and they are dated before the advent of MRI. Hence, it is difficult to ascertain whether these cases represent the “true” intramedullary dermoid cyst as in our case or are part of a developmental defect.