General
- They are commonly derived from retained surface ectoderm trapped by two fusing neuroectodermal surfaces during neural tube closure, and are also termed congenital ectodermal inclusion cysts.
- Theories of origin
- Primary failure of neural tube closure in the third to fifth week of embryogenesis OR
- An earlier primary failure of gastrulation that would explain the associated mesodermal abnormalities
- Implantation dermoids:
- Epidermoid cysts are acquired lesions derived from iatrogenic implantation of surface ectoderm
- Both exhibit slow, linear growth,
- But dermoid cysts typically present at an earlier age with a shorter duration of symptoms.
- Malignant transformation
- Malignant transformation of dermoid and epidermoid cysts is a rare but recognized cause of intracranial squamous cell carcinoma, after metastases and extension from the cranial base.
- Radiotherapy is considered to confer a modest survival benefit
- Leptomeningeal carcinomatosis has only been seen with malignant transformation of epidermoid cysts and is associated with a particularly poor prognosis.
- Should be considered in any patient who does not recover as expected from surgery and who deteriorates in the absence of hydrocephalus with rapid recurrence of the tumour or where imaging shows enhancement at the tumour site.
Classification
Features | Intracranial Epidermoid Cysts | Intracranial Dermoid Cysts |
Frequency | More common 0.5–1.5% of brain tumors | Rare 0.3% of brain tumors |
Location | Off midline (CP angle) | Midline |
Presentation | Later | Earlier |
Origin | Congenital (arising from ectodermal inclusion during neural tube closure) | Embryonic ectoderm trapped in the closing neural tube between the 5th to 6th weeks of gestation |
ㅤ | Acquired (post-surgical or post-traumatic implantation) | ㅤ |
Lining | Simple skin cells, devoid of cutaneous-type adnexal structures Stratified squamous epithelium | Stratified squamous epithelium, containing epidermal appendages (hair follicles, sweat glands, sebaceous glands) |
Contents | Keratin, cellular debris, cholesterol, occasional hair No dermal elements: | Same as epidermoid, plus hair and sebum Dermal elements: Hair follicles, sweat glands, sebaceous glands (secreting sebum) |
Rupture | Less common | More common |
Meningitis | May have recurrent aseptic meningitis, including mollarets meningitis | May have repeated bouts of bacterial meningitis |
Associated anomalies | Tend to be isolated lesions | Associated with other congenital anomalies in up to 50% of cases |
Imaging Appearance | Identical to the petrous apex and middle ear congenital cholesteatomas | Well-defined lobulated midline masses with low attenuation (fat density) on CT and high signal intensity on T1-weighted MR images |
CT | Hypodense, slightly greater than CSF | Hypodense, similar to CSF |
ㅤ | Bone erosion in 33% | Lobulated margins |
ㅤ | No enhancement | Fine linear strands |
ㅤ | No enhancement | |
T1W MRI | Isointense, same as CSF | Typically hyperintense, same as fat |
ㅤ | Occasionally hyperintense around periphery; | No enhancement |
ㅤ | No enhancement | |
T2W MRI | Isointense or hyperintense, same as CSF | Variable |
FLAIR | Variable | Variable |
DWI | Restricted diffusion, hyperintense to CSF | Restricted diffusion, hyperintense to CSF |
Fat Saturation Sequence | Unchanged | High signal drops out |
Local Findings | Insinuates between neurovascular structures | More mass effect |
ㅤ | ㅤ | Associated abnormalities (e.g., Klippel-Feil, dermal sinus tract) |
Enhancement After Contrast | Not specified in the provided information | Typically do not enhance |
Associated abnormalities | Absent | May be present |
Surgical resection | Difficult | Less difficult |
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