Dermoid cysts

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Dermoid

  • 1. Less common than epidermoid cysts (1:4); are usually midline and occur in the fontanelle, fourth ventricle or cauda equina; occur as a result of neural ectoderm being folded in during neurulation – communication of the cyst with the exterior via a sinus tract predisposes the patient to bacterial meningitis
  • 2. Are usually well demarcated from surrounding structures, with smooth wall encasing soft, greasy material (sebaceous glands) which may contain hairs
  • 3. Dermoids typically become symptomatic during the first 2 decades of life due to their abundant production of oily secretions while epidermoids tend to delay their central nervous system presenation until later in life because of their slower production of keratin; dermoids are generally associated with other congenital malformations
  • 4. Dermoids and epidermoids are different from teratomas in that teratomas have primitive germ cells from all three germinal layers while dermoids and epidermoids have remmants of just ectoderm
  • 5. dermoids usually show high signal on T1-weighted images while epidermoids usually do not (look for fat signal to differentiate dermoids from other tumors)
  • 6. dermoids may rupture and fatty material may be scattered throughout the ventricular and subarachnoid spaces

Epidermoid

  • 1. mainly intracranial in the cerebellopontine (CP) angle, parasellar region and cranial diploe
  • 2. epidermoids have a smooth gray surface and friable waxy material inside; usually envelop adjacent structures while dermoid cysts are usually well demarcated from surrounding structures
  • 3. both dermoid and epidermoid can present as painless, mobile, rubbery masses on the scalp that only cause cosmetic deformity
  • 4. tend to be hypointense to brain on T1-weighted images and bright on T2; hallmark is diffusion restriction which can help differentiate it from an arachnoid cyst.
  • 5. operative removal of both dermoid and epidermoid tumors requires careful attention to preventing contents of the cysts to be spilled into the subarachnoid space; seeding of the subarachoid space can lead to a chemical meningitis or ventriculitis that can be long lasting
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