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Dermoid Cyst

Summary

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  • Benign congenital lesion containing mature tissue derived from ectoderm, mesoderm, and endoderm
  • Most commonly found in ovaries, but can occur anywhere along the midline of the body
  • Imaging typically shows a cystic mass with fat-fluid levels and calcification1

Pathophysiology

  • Arise from trapped embryonic germ cells during fetal development
  • Contain mature tissues such as:
    • Hair follicles
    • Sebaceous glands
    • Sweat glands
    • Teeth
    • Bone
    • Thyroid tissue
  • Lined by keratinized squamous epithelium
  • Slow-growing, but can rupture causing inflammation or malignant transformation (rare)

Demographics

  • Intracranial dermoids are rare (~0.5% of intracranial tumours), typically midline
  • Common sites: parasellar/suprasellar, frontonasal and posterior fossa

Diagnosis

  • Often incidental; may present with mass effect or, if ruptured, chemical meningitis or seizures
  • Rupture disseminates fat into the subarachnoid space and ventricles

Imaging

  • CT: fat-attenuation lesion (−20 to −120 HU), often with mural calcification
  • MRI:
    • T1 hyperintense (fat), suppressing on fat-saturated sequences; chemical shift artefact
    • Rupture produces scattered T1-hyperintense fat droplets in the sulci and ventricles (fat–fluid levels), a pathognomonic finding

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  • A 30-year-old patient presented with an acute onset headache.
  • MRI showed a lesion in the right cavernous sinus that was T1-hyperintense that suppressed on the fat-suppressed FLAIR imaging, consistent with fat content.
  • There were further locules of fat signal over the cerebral hemispheres consistent with dermoid cyst rupture.

Treatment

  • Surgical excision with careful avoidance of spillage (which provokes chemical meningitis)

Differential diagnosis

Imaging differential Differentiating feature
Intracranial lipoma Homogeneous fat without calcification; does not rupture/disseminate
Epidermoid cyst Follows CSF signal and restricts on DWI; no fat
Teratoma Heterogeneous with fat, calcification and enhancing soft tissue
Ruptured Rathke's cleft cyst / craniopharyngioma T1-bright from proteinaceous content, but no macroscopic fat or disseminated droplets

  1. Pepe et al. Mastoid Dermoid Cyst. 2020. The journal of international advanced otology - Open in new tab. ↩