DERMOIDS

Dermoids – Types and Key Features

1. Sequestration Dermoids (Congenital)

 Etiology: Inclusion of epithelium along lines of embryonic fusion → cyst formation.

 Sites:

o Forehead, neck, postauricular region

o External angular (frontal–zygomatic suture)

o Internal angular (frontonasal suture, root of nose)

o Sublingual, submental (fusion of 1st and 2nd branchial arches)

o Midline sites (scalp, skull, spine, anywhere along embryonic fusion)

 Skull dermoids:

o Entirely outside skull

o Outside with bone defect ± dura attachment

o Dumbbell type (inside & outside with stalk)

o Entirely intracranial (rare)

 Clinical features:

o Painless, cystic, fluctuant, smooth swelling

o Non-transilluminating

o Resorption/indentation of bone beneath

o Paget’s test: yielding sensation on indentation

o Intracranial extension → cough impulse

 Differentials: Sebaceous cyst, lipoma, neurofibroma, thyroglossal cyst (for submental)

 Investigations: X-ray, CT/MRI

 Treatment: Excision (often neurosurgical craniotomy if intracranial extension)

 External angular dermoid: Over external angular process; eyebrow overlaps part of
swelling; may extend into orbit; DDx = lacrimal gland swelling.

 Internal angular dermoid: Near root of nose (frontonasal suture); DDx = lacrimal sac
swelling, frontal sinus mucocele.

 Sublingual/Submental dermoid: Midline swelling, soft, cystic, non-transilluminating, not

Complications: infection, hemorrhage, rupture, surface ulceration, calcification, pressure effects

2. Tubulodermoids (Remnants of Embryonic Tubes)

 From unobliterated congenital ducts or ectodermal tubes.

 Examples:

o Thyroglossal cyst: persistent thyroglossal duct

o Ependymal cyst (rare, neuroepithelial, may → hydrocephalus)

o Post-anal dermoid: Remnant of neuroenteric canal, in front of sacrum/coccyx

o Urachal cyst: Remnant of urachus → midline extraperitoneal swelling (can

 Features: Soft, cystic midline swellings; may get infected or cause pressure symptoms.

 Treatment: Complete excision ± coccygectomy in post-anal dermoid.

3. Implantation Dermoids (Acquired)

 Etiology: Trauma → epidermis buried into subcutaneous tissue → cyst formation.

 Sites: Fingers, toes, feet (common in tailors, gardeners).

 Features:

o Small, firm, mobile, painless swelling

o Often after forgotten minor trauma

 Complications: Infection, rupture, digital nerve compression.

 Differentials: Lipoma, bursa

 Treatment: Surgical excision under local anesthesia

4. Teratomatous Dermoids (True Dermoid Cysts)

 Arise from totipotent germ cells → contain tissues of all 3 germ layers (ectoderm,
mesoderm, endoderm).

 Sites: Ovary, testis, retroperitoneum, mediastinum.

 Contents: Hair, teeth, cartilage, sebaceous material, muscle.

 Nature: May be benign (mature cystic teratoma) or malignant.

PG Exam Pearls

 Sequestration dermoid = embryonic fusion line cyst

 Angular dermoids: external type more common than internal; eyebrow sign in external
angular dermoid

 Submental dermoid DDx: thyroglossal cyst, submental abscess, sebaceous cyst

 Skull dermoids: can erode bone ± communicate with intracranial cavity

 Implantation dermoid = acquired (post-trauma inclusion of epithelium)

 Teratomatous dermoid = true germ-cell tumor (ovary/testis commonest sites)

 Treatment: Complete excision ± neurosurgical approach if intracranial/intrathoracic

NEUROFIBROMA
Neurofibroma

Definition

 Benign tumor of peripheral nerve sheath, containing ectodermal (Schwann cells),

 May be solitary or multiple (Neurofibromatosis).

Sites

 Cranial nerves (esp. trigeminal)

 Spinal nerves – most common intradural extramedullary spinal tumor

 Peripheral nerves – cutaneous or subcutaneous

Neurofibromatosis

 Type 1 (von Recklinghausen’s disease):

o Chromosome 17 mutation; autosomal dominant

o Multiple cutaneous + plexiform neurofibromas

o Café-au-lait spots (>5, >1.5 cm = diagnostic)

o Axillary/groin freckles, Lisch nodules in iris

o Associated: scoliosis, bone cysts, pheochromocytoma (20%), MEN IIb

o Risk of malignant peripheral nerve sheath tumor (~5%)

 Type 2 (acoustic NF):

o Chromosome 22 mutation

o Bilateral vestibular schwannomas

Types of Neurofibroma
 1. Nodular (solitary):

o Firm, fusiform swelling along nerve

o Moves perpendicular but not longitudinal to nerve

o Pain, hyperesthesia along course of nerve

2. Plexiform:

o Along branches of 5th cranial nerve (esp. ophthalmic division, face)

o Large, bag-of-worms swelling with thickened pendulous skin

o Causes bone/orbit erosion, cosmetic deformity, trigeminal paraesthesia

o Variant pachydermatocele → thickened edematous pigmented skin folds

o Associated with café-au-lait spots

3. Elephantiatic neurofibroma:

o Congenital, limb involvement with coarse, thick skin

4. Cutaneous neurofibroma:

o Multiple, small firm nodules all over body, sometimes pedunculated

o May occur on scalp → “turban tumor”

Clinical Features

 Subcutaneous/cutaneous painless swelling, round/oval/fusiform

 Moves across but not along the nerve

 Mild pain, tingling, or paraesthesia in distribution

 Skin normal unless cutaneous type

 Complications:

o Cystic degeneration, hemorrhage, bone/soft tissue erosion

o Spinal involvement → cord compression & paralysis

o Malignant change (~5%): rapid growth, vascularity, pain, fixity, lung metastases
Important Associations

 Café-au-lait spots → common neuroectodermal origin (also in McCune-Albright)

 Phaeochromocytoma with hypertension (~20%)

 Kyphoscoliosis in NF-1 familial cases

 MEN IIb: eyelid/lip neurofibromas with medullary carcinoma thyroid

 Intestinal neurofibroma may cause intussusception

Diagnosis

 Clinical + imaging (MRI spine/skull for extent)

 Histopathology (Schwann cells + fibroblasts, all nerve components proliferate)

Treatment

 Indications:

o Symptomatic (pain, neurological deficit)

o Cosmetic deformity

o Recent rapid increase in size

o Suspicion of malignant transformation

 Procedure: Excision under GA/RA

o Solitary – excision feasible

o Multiple plexiform – surgery difficult, recurrence common

PG Exam Pearls

 Most common spinal tumor = Neurofibroma

 Distinction: Neurofibroma = horizontal mobility only; Schwannoma = mobility in all

 5% risk of sarcomatous transformation (esp. plexiform NF-1)

 NF-2 = bilateral acoustic schwannomas

 NF frequently associated with pheochromocytoma → check before anesthesia