Dermoid Cyst

Definition and Pathogenesis

A dermoid cyst is an epithelial-lined congenital cyst formed by sequestration of ectodermal tissue along embryonic fusion planes during development. The cyst wall is lined by keratinizing stratified squamous epithelium and — critically — contains mature adnexal structures (pilosebaceous units, sweat glands, hair follicles, smooth muscle), which distinguishes it from an epidermoid cyst (no adnexal structures).

They are a separate entity from benign cystic teratomas (ovarian "dermoids"), which are neoplasms derived from all three germ layers. — Dermatology 2-Volume Set 5e

Classification

Type	Origin	Notes
Congenital/inclusion dermoid	Fusion plane entrapment	Most common; head/neck, periorbital, midline
Tubulodermoid	Entrapment around embryonic tubular structures	Spinal/sacral region
Implantation (acquired) dermoid	Traumatic implantation of surface ectoderm	Fingertip/hand after thorn prick or needle injury
Ovarian (mature cystic teratoma)	Germ cell origin	Neoplasm — see below

Cutaneous / Craniofacial Dermoid Cysts

Sites

Occur along embryonic closure zones:

Lateral eyebrow (external angular dermoid) — most common
Nasal root / dorsum of nose (fistula of the dorsum of the nose)
Midline forehead, scalp (frontal → occipital)
Mastoid process, floor of mouth, neck midline
Chest, back, abdomen, perianal/sacral area, scrotum

Clinical Features

Firm, non-compressible, non-pulsatile subcutaneous nodule, 1–4 cm
Does not transilluminate
Mobile under skin but often tethered to underlying periosteum
No attachment to overlying skin
A punctum or hair-tufted pit may be present → signifies underlying sinus
Present within first year of life; 70% identified by age 5

Intracranial Extension ⚠️

Nasal and midline scalp dermoids have ~25% overall risk of intracranial extension
If a sinus ostium is present → risk rises to ~50%
A nasal dermoid may extend to widen the nasal bridge
Spinal dermoid/sinus may connect to subarachnoid space → risk of meningitis
Intracranial dermoids can rupture → chemical meningitis or hydrocephalus from keratinous/sebaceous CSF contamination

Nasal and eyebrow dermoids may run in families (genetic component).

Orbital Dermoid Cyst

An orbital dermoid is a choristoma — histologically normal tissue in an abnormal location — displaced ectoderm along embryonic lines of closure.

Fig. — Superficial orbital dermoid cyst in a child (Kanski's Clinical Ophthalmology)

Superficial vs. Deep

Feature	Superficial	Deep
Presentation	Infancy; painless nodule	Adolescence/adult; proptosis or acute inflamed orbit
Location	Superotemporal > superonasal orbit	Posterior to orbital septum
Exam	Firm, 1–2 cm, mobile, posterior margin palpable	Proptosis, dystopia, indistinct posterior margins
Imaging	Well-circumscribed heterogeneous cystic lesion	Well-circumscribed; may extend intracranially via bony defect

Treatment: Excision in toto. Take care not to rupture the cyst wall — leakage of keratin causes severe granulomatous inflammation in surrounding tissue.

Histopathology

Wall: keratinizing stratified squamous epithelium
Contents: keratin debris, hair shafts, sebaceous material
Wall structures: pilosebaceous units, apocrine/eccrine glands, smooth muscle bundles
Portions of the wall may show a "shark tooth" (wavy eosinophilic) pattern resembling steatocystoma — Andrews' Diseases of the Skin

Ovarian Dermoid Cyst (Mature Cystic Teratoma)

The most common benign ovarian neoplasm in reproductive-age women. Strictly a germ cell tumor containing tissues from all three germ layers, but dominated by ectodermal derivatives.

Gross pathology of ovarian mature cystic teratoma — inner surface lined with greasy hair, sebaceous material, and a Rokitansky protuberance

Gross pathology: ovarian dermoid cyst opened to show hair, sebaceous material, and Rokitansky protuberance

Key Features

Contains: hair shafts, sebaceous material, teeth (odontogenic tissue), neural tissue
Rokitansky protuberance (dermoid plug): mural nodule from which teeth and hair arise — pathognomonic on gross examination
~60% are clinically asymptomatic (found incidentally)
Bilateral in ~10–15% of cases

Complications

Ovarian torsion — most common complication
Rupture → chemical peritonitis
Infection
Malignant transformation — rare (<2%), more common with advanced age
Paraneoplastic anti-NMDA receptor encephalitis — when neural elements express NMDA-R antigens

Imaging

Ultrasound: hyperechoic plug with posterior shadowing (Rokitansky protuberance); dermoid mesh pattern
CT/MRI: fat attenuation/signal within the lesion is diagnostic; fat-fluid level, calcification (teeth)

Management

Laparoscopic ovarian cystectomy — appropriate regardless of size; preserves fertility
Oophorectomy — for larger cysts replacing the entire ovary
Laparotomy — for very large cysts or when malignancy cannot be excluded

Cervical / Neck Dermoid

Usually midline of the neck, asymptomatic
Does not elevate with tongue protrusion (distinguishes from thyroglossal duct cyst, which does)
May become acutely infected
Treatment: Simple cystectomy after resolution of acute infection

Differential Diagnosis

Lesion	Distinguishing Feature
Epidermoid cyst	No adnexal structures on histology
Pilonidal cyst	Midline sacral, symptomatic in adolescence
Thyroglossal duct cyst	Elevates with tongue protrusion/swallowing
Branchial cleft cyst	Lateral neck; lymphoid follicles on histology
Encephalocele	Pulsatile, compressible, impulse on coughing
Nasal glioma	No intracranial connection (usually)
Hemangioma	Vascular, compressible, may involute

Imaging Guidelines

Preoperative imaging (CT first, followed by MRI if bony changes found) is mandatory before excision for:

Midline nasal dermoids
Midline scalp dermoids
Posterior spinal dermoids
Any lesion with a draining sinus ostium

Lateral eyebrow dermoids generally do not require pre-excision imaging.

Treatment Summary

Site	Treatment
Periorbital/facial	Surgical excision in toto; neurosurgery consult if intracranial extension
Nasal/scalp midline	Preoperative CT/MRI mandatory; neurosurgery if CNS connection
Neck midline	Simple cystectomy
Spinal	MRI to exclude tethered cord; neurosurgical excision
Ovarian	Laparoscopic cystectomy; oophorectomy for large/whole-ovary replacement

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