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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 calcification

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

  • Most common in women of reproductive age (20-40 years)
  • Ovarian dermoids account for 10-20% of all ovarian neoplasms
  • Intracranial dermoids represent 0.5-1% of all intracranial tumours
  • Can occur in both sexes and all age groups, but less common in men and children

Diagnosis

  • Often asymptomatic and discovered incidentally
  • Symptoms depend on location and size:
    • Abdominal pain or pelvic pressure (ovarian dermoids)
    • Headache, seizures, or focal neurological deficits (intracranial dermoids)
    • Visible or palpable mass (cutaneous dermoids)
  • Laboratory tests:
    • Elevated CA-125 in some cases of ovarian dermoids
    • Alpha-fetoprotein and beta-hCG to rule out germ cell tumours

Imaging

  • CT:
    • Fat-fluid levels
    • Calcification
    • Fat attenuation within lesion (-20 to -120 HU)
  • MRI:
    • T1-weighted: hyperintense fat components
    • T2-weighted: variable signal intensity
    • Fat suppressed sequences: useful for confirming fat content
    • Chemical shift artefact at fat-fluid interface

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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 is the primary treatment
    • Laparoscopic or open approach for ovarian dermoids
    • Craniotomy for intracranial dermoids
    • Simple excision for cutaneous dermoids
  • Careful handling during surgery to prevent spillage and chemical peritonitis
  • Fertility-sparing surgery for ovarian dermoids in young women
  • Regular follow-up imaging for incompletely resected intracranial dermoids
  • Malignant transformation is rare (<2%) but requires aggressive treatment if occurs

Differential diagnosis

Differential Diagnosis Differentiating Feature
Epidermoid cyst Lacks dermal appendages on histology
Teratoma Contains tissue from all three germ layers
Pilonidal cyst Typically occurs in sacrococcygeal region
Lipoma Homogeneous fat density on CT/MRI
Sebaceous cyst Typically smaller and more superficial
Ganglion cyst Lacks fat content, associated with joint or tendon sheath
Branchial cleft cyst Located along anterior border of sternocleidomastoid muscle
Thyroglossal duct cyst Moves with swallowing, midline neck location
Abscess Surrounding inflammatory changes, no fat content
Lymphangioma Fluid-filled spaces without fat content