Dermoid of Skull
Epidermoid Inclusion Cyst

General Considerations

• Benign, slow-growing tumors of the skull (“cyst” and “tumor” are used interchangeably)
• Believed to occur secondary to aberrant epidermal or dermal inclusion in the calvarium
• Although rare, it is still , along with Langerhans cell histiocytosis, one of the more common lesions in the pediatric skull

Clinical Findings

• Most often present between 20-40 years of age, dermoids slightly earlier than epidermoids
• Painless subcutaneous swelling is most common presentation
• If large enough, they can compress cranial nerves

Imaging Findings

• Intradiploic
• Well-demarcated lytic lesions which tend to expand both the inner and outer  tables and demonstrate sclerotic borders
• Epidermoid cysts occur in bones of the skull in this order of frequency
  • Parietal bone
• Frontal bone
• Occipital bone
• Orbit
• Dermoid cysts tend to be midline in the frontotemporal and then parietal locations
• Most involve the course of a suture line near the anterior fontanelle
• On CT, they are hypodense and non-enhancing
• On MRI, they are low intensity on T1 and high on T2

Differential Diagnosis

• Langerhans cell histiocytosis (eosinophilic granuloma)

Treatment

• Surgical removal or curettage

Complications

• May communicate with sinuses
  • Best imaged with MRI
• Rarely may become infected
• Rarely may involve underlying dural sinuses
• Associated with Klippel-Feil syndrome

Prognosis

• Excellent

Dermoid Cyst of the Skull. Top. Well-demarcated, lytic lesion of the diploic space (white arrows) expanding the outer table adjacent to the midline. Lower. Same lesion as seen on the scout image of the CT (yellow arrow) is seen in the frontal bone expanding the diploic space.
For these same photos without the arrows, click here and here
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SE Gibson and RA Prayson. Primary Pediatric Skull Lesions. Arch Pathol Lab Med:  Vol 131, May 2007