Dermoid Cyst

Etiology

The etiology of dermoid cysts remains mostly unknown. The cause of this congenital developmental anomaly has yet to be determined.[3][4] Dermoid cysts are true hamartomas. These occur when skin and skin structures become trapped during fetal development. Prior et al. did not find any correlation between the localization of the dermoid cyst and sex, histology, or age of the patient.[4]

Epidemiology

Dermoid cysts are among the most common pediatric skull tumors.[4][3] Dermoid cysts account for about 15.4%-58.5% of all scalp and skull masses in pediatric patients.[4] Dermoid cysts are usually congenital, with about 70% of cases discovered in children five years old or younger.[3][6] Cases of dermoid cysts discovered in adulthood have also been reported.[3][4] Pollard et al. found a slight predominance of dermoid cysts in girls.[5] However, this significant predominance has not been seen in other case series.[3] No racial predilection is apparent; however, most cases are described in Whites.

Pathophysiology

Dermoid cysts result from an abnormal alteration in fetal development.[2][4] They occur due to the abnormal sequestration and inclusion of the surface ectoderm along the lines of skin fusion during embryologic development.[4][2][7] Due to this abnormality, a dermoid cyst can usually be found along cranial sutures or the anterior fontanelle.[4][2] 

Histopathology

Dermoid cyst on histology shows a well-defined wall lined by stratified squamous epithelium and a lumen that may be filled with mature adnexal structures of mesodermal origin, such as hair follicles and shafts, sebaceous and eccrine glands.[2][4][8]

History and Physical

In the majority of cases, dermoid cysts occur in the head and neck region, although they may be found anywhere on the body.[4][3] In the head and neck region, dermoid cysts can most commonly be seen in the frontal, occipital, and supraorbital areas, with the outer third of the eyebrow being the most frequently affected region.[2][4] An eyelid dermoid cyst attached to a tarsus may present as a firmly adherent non-tender upper eyelid nodule.[9] 

A lower lid dermoid cyst may be evident as a painless, gradually enlarging swelling of the lower lid.[10] Dermoid cysts in the medial canthal area may present as masses adherent to lacrimal canaliculi.[11] 

Dermoid cysts usually occur as solitary lesions; however, multiple concurrent dermoid cysts have also been reported.[2] Dermoid cysts typically present as a pale, flesh-colored, pearly, dome-shaped, firm, deep-seated, subcutaneous nodule.[1][2][3][12] They are usually asymptomatic, non-pulsatile, and non-compressible.[1][2]

Hair protruding from a dermoid cyst punctum is pathognomic for dermoid cysts.[13] Of note, midline dermoid cyst may present as a pit that secreted sebaceous material that can become intermittently inflamed and infected.[3][13]

Evaluation

Dermoid cysts have the potential to grow over time and extend intracranially or intraspinally.[1][3] Due to this potential, one should consider radiological studies before biopsy or manipulation, especially of a lesion that is midline or on the scalp.[3][1] Aspiration or biopsies of dermoid cysts have the potential to cause infection, further leading to osteomyelitis, meningitis, or cerebral abscess.[3][4][14] Other possible complications include bony erosions, eyelid displacement, and intracranial extension.[3][15]

Midline dermoid cysts have the highest association with cranial or spinal dysraphism or have an intracranial extension.[3] Nasal dermoid cysts are the most frequent midline congenital nasal malformations.[3] Studies have shown that there is a 10-45% incidence of intracranial extension in patients with a nasal dermoid cyst.[1] When undergoing neuroimaging, MRI is the preferred means of revealing evidence of intracranial or intraspinal extension.[1][3] Studies showed a higher association between a dermoid cyst located in the frontal and pterional regions and bony erosion.[4][16] If bony erosion is suspected, CT imaging is better at delineating these bony changes.[3][4] In some instances, high-resolution ultrasonography may help reveal a deep component.[3] 

Dermoid cysts under an ultrasound will show a well-defined homogenous and hypoechoic cystic lesion.[2] Fistulography was done preoperatively in some cases to rule out the involvement of a deep tract in a dermoid cyst.[3] Dacryocystography was also performed in some atypical dermoid cysts cases.[3] Furthermore, consultation with a neurosurgeon is highly recommended for dermoid cyst complicated by intracranial or intraspinal extension.[1][3]

Treatment / Management

Dermoid cysts usually tend to grow slowly, further having the potential to cause bony deformities, intracranial extension, or intraspinal extension.[1][4] The presence of intracranial extension or intraspinal extension can further lead to meningitis or develop into an abscess.[1][3] A small, asymptomatic dermoid cyst may not necessitate immediate excision as it can be stable for years or even regress.[3][17] However, because most dermoid cysts grow over time, complete surgical excision without disruption of the cyst wall by an experienced surgeon is recommended before the development of such complications.[3][4](B2)

Early resection may also avoid extensive surgery and a shorter skin incision, further resulting in an improved cosmetic outcome.[3][4] An additional advantage of surgical excision is the possibility of obtaining a histologic diagnosis due to the rare possibility of a malignant tumor presenting as a solitary lump in the head and neck region of a child like a dermoid cyst.[4] The most dermoid cysts can be removed using a direct approach with careful dissection at the site where the cyst adheres to the bone.[3] If the cyst wall ruptures at the time of surgical removal, then remnant tissue should be removed using curettage and copious irrigation.[3](B2)

If the cyst wall has adhered to vital structures, a partial excision may be performed.[3] Recurrences of dermoid cyst have been seen in cases of incomplete excision.[3] Another benefit of early removal of dermoid cysts is a higher chance of obtaining a complete excision without disruption of the cyst wall, a factor associated with a reduced risk of recurrence.[3][4] For small dermoid cysts, endoscopic surgery is a novel approach for removal.[3] In cases of a dermoid cyst with intracranial extension, a craniotomy may still be required.[3](B2)

Differential Diagnosis

Dermoid cysts are rare, but all nodular cystlike lesions are included in the differential diagnoses of a patient presenting with a subcutaneous nodule, especially in the head and neck or midline region.[1][2][3] Following are the differentials of a dermoid cyst:

• Epidermoid cyst
• Glioma
• Encephalocele
• Juvenile xanthogranuloma
• Lipoma
• Pilar cysts
• Meningioma
• Neurofibroma
• Teratoma
• Rhabdomyosarcoma
• Olfactory neuroblastoma
• Lymphoma
• Subcutaneous abscess
• Facial trauma
• Trichilemmal cyst
• Pilomatrixoma
• Lymphatic malformation
• Thyroglossal duct cyst

Prognosis

The overall prognosis for patients with a dermoid cyst is good, especially when there is no intracranial or intraspinal extension.[3] Although histologically benign, dermoid cysts may grow and erode the skull, further being potentially susceptible to the epidural extension.[4] When there is intracranial or, intraspinal extension overall prognosis is still good if there is proper, timely surgical intervention.[3][4] In rare instances, when dermoid cysts become symptomatic due to local mass, effect, rupture, infection, or even in rare cases, cause brain compression prognosis can be poor.[3][4]

Complications

There are no complications for dermoid cysts that don't have an intracranial or intraspinal extension.[3][4] Dermoid cysts that have intracranial or intraspinal extension may lead to meningitis, abscess, or cause local mass effect.[3][1][4] Aspiration and biopsies of dermoid cysts have the potential to cause infection, further leading to osteomyelitis, meningitis, or cerebral abscess.[1][3]

Other possible complications include bony erosions, eyelid displacement, and intracranial extension.[3] Malignant transformation is a rare complication that may occur in patients with long-standing dermoid cysts. Carcinomatous transformation to squamous cell carcinoma is described in sublingual, ovarian, and intra-abdominal dermoid cysts.