Intracranial dermoid cyst
The tumors typically arise in infants to young adults because of their congenital origin 1) 2) 3). Intracranial dermoid cyst are very rare, constituting less than 1% of intracranial tumors 4), and are relatively rare in middle-aged or older people 5).
Dermoid cysts are thought to occur as a developmental anomaly in which embryonic ectoderm is trapped in the closing neural tube between the 5th-6th weeks of gestation.
Dermoid cysts, like epidermoid cysts, are lined by stratified squamous epithelium. Unlike epidermoid cysts, however, they also have epidermal appendages such as hair follicles, sweat and sebaceous glands. The latter handles the secretion of sebum that imparts the characteristic appearance of these lesions on CT and MRI.
A common misconception is that dermoid cysts contain adipose tissue. This is not the case, as lipocytes are mesodermal in origin, and dermoid cysts (by definition) are purely ectodermal. A dermoid cyst with adipose tissue would be a teratoma.
Associated dermal sinuses cause earlier onset of clinical symptoms such as infection 10). Other common symptoms including headaches, seizures, and chemical meningitis, and visual disturbances occur late in the clinical course because of its slow-growing nature 11) 12) 13).
Many intracranial dermoid cysts are asymptomatic and only found incidentally. Often there is a long history of vague symptoms, with headache being a prominent feature
In case of rupture (spontaneous, traumatic, or iatrogenic (at resection)) leakage of sebum into the subarachnoid space results in an aseptic chemical meningitis.
The presentation is variable, ranging from a headache, to seizures, vasospasm and even death 14).
Occasionally, dermoid tumors are incidentally discovered on computed tomography (CT) of the brain or magnetic resonance imaging (MRI) following unrelated clinical complaints. They are also discovered during radiologic investigations of unexplained headaches, seizures, and rarely olfactory delusions.
On imaging, they are usually well-defined lobulated midline masses that have low attenuation (fat density) on CT and hypersignal on T1-weighted MRI images. Typically they do not enhance after contrast administration.
Although dermoid cysts are pathognomonic in appearance on a CT examination, the MRI is also of value in helping to understand the effect of extension and pressure of the mass. DWI is also important for support of the diagnosis and patient follow-up.
Historically, when skull x-rays were routinely used in the assessment of suspected intracranial pathology, a focal lucency due to the fatty sebum
Typically dermoid cysts appear as well defined low attenuating (fat density) lobulated masses. Calcifications may be present in the wall. Enhancement is uncommon, and if present should at most be a thin peripheral rim.
Very rarely they demonstrate hyperdensity thought to be due to a combination of saponification, microcalcification and blood products. This is usually the case when present in the posterior fossa, although why this is the case is not certain.
Unlike intracranial lipomas that follow fat density on all sequences, intracranial dermoids have more variable signal characteristics:
T1 typically hyperintense (due to cholesterol components) droplets in the subarachnoid space may be visible if rupture has occurred
T1 C+ (Gd): generally do not enhance extensive pial enhancement may be present in chemical meningitis caused by ruptured cysts
T2: variable signal ranging from hypo to hyperintense.
Left parasellar extraaxial lesion 2.2 x 1.9 x 1.5 cm without evidence of contrast uptake.
Slight mass effect on the anterior aspect of the left temporal lobe.
Epidermoid cysts at one end (containing only desquamated squamous epithelium) and teratomas at the other (containing essentially any kind of tissue from all three embryonic tissue layers).
Intracranial lipoma: homogeneous fat attenuation/signal intensity, chemical shift artefact
Intracranial teratoma: immature, usually occur in the pineal region
Craniopharyngioma most are strikingly hyperintense on T2, most enhance strongly
Can be surgically excised and provided complete excision is achieved recurrence is uncommon. Sometimes due to local adhesion of the capsule to vital structures, incomplete excision must be performed. Recurrent growth, in either case, is slow 15).
Spontaneous rupture of dermoid tumor is a potentially serious complication that can lead to meningitis, seizures, cerebral ischemia and hydrocephalus.
Extremely rare malignant transformation into squamous cell carcinoma has been reported 21).