MyPACS.net: Radiology Teaching Files > Case 13326409

previously visited 15 Y/O FEMALE WITH HEADACHE
Contributed by: Faculty and residents Children's Hospital, Radiologist, Children's Health System, Birmingham, Alabama., USA.
Patient: 15 year old female
History: Headache
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Findings: Axial NECT (Brain window) -  Midline, predominantly fat density mass within  posterior fossa, centered between the cerebellar hemispheres.  Associated medullary and 4th ventricular mass effect.

Axial NECT (Bone window) - Small, linear cleft through occipital bone near external occipital protuberance, suggestive of possible sinus tract.

Sagittal T2 MR - Midline, mixed signal intensity posterior fossa mass with associated medullary and 4th ventricular mass effect, as well as linear low signal coursing posterior toward skin surface at level of Foramen Magnum (although does not contact skin surface), suggestive of possible sinus tract.
Diagnosis: Dermoid cyst
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

References: www.emedicine.com
StatDX (Amirsys, Inc)
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Additional Details:

Case Number: 13326409Last Updated: 05-06-2008
Anatomy: Cranium and Contents   Pathology: Benign Mass, Cyst
Modality: CT, MRAccess Level: Readable by all users

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