Discussion: · Dermoid tumors are not true neoplasms but are inclusion cysts composed of ectodermal elements.
· Uncommon lesions, accounting for approximately 0.3% of all brain tumors (occur 4-10 times less frequently than do epidermoid tumors).
· Often discussed with epidermoid tumors because of their similar appearance and developmental origin.
· Thought to arise from misplaced ectodermal elements during the third to fifth week of embryonic life, when the neural tube closes at the midline (may explain the frequent midline location of dermoid tumors). In contrast, epidermoid tumors are often located lateral to the midline of the cranium.
· More commonly associated with dermal sinus tracts and spinal abnormalities than are epidermoid tumors.
· Slight M>F. Avg age at dx - 20 (v. 40-50 for epidermoid)
· Benign, slow-growing lesions that rarely undergo malignant transformation (SCCA). Can rupture -> chemical meningitis. Meningitis also caused by dermal sinus tract infection (more common if contacts skin surface).
· Imaging:
- Fat density on CT, follows fat on MR
- Most often midline
- Approx 20% calcify
- No/little enhancement; macroscopic fat
- Off midline? Follows CSF on MR? Restricted diffusion? Think epidermoid
· Tx - complete surgical excision.
- Residual capsule may lead to recurrence
- Rare SCCa degeneration within surgical remnants
· Classic presentation: Young pt - HA's, older - seizures
