Dermoid and epidermoid cysts

General features:
Dermoid cysts have skin appendages like sebaceous glands or hair follicles within the wall, not present in epidermoid cyst and much less common than dermoids in neck
7% of dermoid cysts occur in head and neck
Most common site is lateral eyebrow
2nd most common location (10%) is floor of mouth

Clinical features:
Dermoids present in 2-3 decade, epidermoids in infancy

Location:
Most common in floor of the mouth
Midline, superior to hyoid

Clinical presentation:
Slow growing mass
Rapid growth may occur due to pregnancy or sinus tract
Soft, mobile mass not attached to skin
Do not move with tongue

Imaging:
Thin-walled unilocular in submandibular or sublingual space

CT:
Low attenuation fluid material with or without fat globules
'Sack of marbles' appearance is pathognomonic
Fat-fluid level may be seen
May enhance

MR:
Most located superior to mylohyoid, less commonlay inferior to it (coronal plane is best)
Variable signal T1

Complications:
5% to squamous cell carcinoma

References:
1. Koeller KK et al. Congenital Cystic Masses of the Neck: Radiologic-Pathologic Correlation. Radiographics. 1999;19:121-146