Dermoid cysts are congenital lesions that commonly arise from nondisjunction of surface ectoderm from deeper neuroectodermal structures. They tend to be found along planes of embryonic closure. Classification by site is helpful for diagnostic planning and surgical treatment. A distinction can be made between frontotemporal, orbital, frontoethmoidal, and calvarial lesions. The risk of extension into deeper tissues must be determined before surgical intervention. Simple lesions are amenable to direct excision. Deeper lesions often require a coordinated surgical approach between a neurosurgeon and craniofacial surgeon after thorough radiographic imaging. Follow-up through the developmental years is recommended for complex dermoid lesions.
Dermoid lesions in the craniofacial and orbital region comprise a spectrum of pathologic conditions that range from extraorbital extracranial cysts to complex sinus tracts extending intracranially.
The goals of surgical treatment include complete excision to obtain the proper histopathologic diagnosis, prevent recurrence, and for select lesions, prevent neurologic complications.
Cranio-orbital lesions in the midline pose a higher risk for penetration of the facial skeleton with coincident neurologic involvement requiring special attention.
Simple lesions are amenable to direct excision. Deeper lesions may require a coordinated surgical approach between a neurosurgeon and craniofacial surgeon after characterization by radiographic imaging.
Dermoid lesions of the craniofacial region comprise a spectrum of pathologic conditions that range from simple localized cysts to complex lesions with fistula formation and intracranial extension. When encountered in children, they are commonly considered to be congenital in nature and to arise from active ectodermal cell rests that are trapped in an abnormal position.
When considering all dermoids, 7% arise in the head and neck, and more than half will be diagnosed before 6 years of age. Additionally, when including orbital rim lesions, numerous reports in children identify the dermoid cyst as the most commonly encountered orbital lesion.
Congenital dermoids in the head and neck are classified as periorbital, nasal, submental, and midventral/middorsal neck. More focused approaches to the craniofacial region have highlighted nasoglabellar, orbital, and frontotemporal occurrences. Within these craniofacial groups, pathologic conditions as varied as epidermal inclusion cysts, encephaloceles, gliomas, eosinophilic granulomas, lipomas, neurofibromas, and hemangiomas may overlap with respect to clinical presentation.
Often the simple dermoid cyst remains asymptomatic but when neglected may exhibit a slowly progressive nature resulting in pain, hard or soft tissue distortion, functional impairment, or drainage with or without infection. The more rarely encountered dermal sinus tract also harbors the notable potential for morbid neurologic complications including tumor formation, meningitis, or brain abscess if improperly managed.
The goals of surgical treatment include complete excision to obtain proper histopathologic diagnosis, prevent recurrence, and for select lesions, prevent neurologic complications. Given the congenital nature of these lesions, their relative frequency, and the range of pathologic conditions that must be differentiated, the pediatric craniomaxillofacial surgeon must be familiar with their presentation and management.
Dermoid cysts are cystic neoplasms that demonstrate ectodermal and mesodermal features. This is in contrast to epidermal inclusion cysts, which only include ectodermal elements, or teratomas, which have ectodermal, mesodermal, and endodermal components. More precisely, dermoid cysts are lesions with a stratified squamous epithelial lining in a fibrous connective tissue that includes skin adnexa, such as hair follicles, sebaceous glands, or sweat glands ( Fig. 1 ). The lumen often contains keratin or sebaceous material produced by these components. The cyst is usually subcutaneous and is often adherent to the periosteum overlying a craniofacial suture.
Dermoid cysts may be congenital in origin or, more rarely, acquired. The congenital dermoid in the craniofacial region most often is thought to be of an inclusion type whereby epithelial remnants are sequestered abnormally to a deeper location. In contrast, the teratoma type of congenital dermoid is primarily found in the ovaries or testes and is derived from displaced cells in the blastomere.
Focusing on congenital inclusion dermoids, the embryologic origin stems from the activation of ectodermal cells dislocated secondary to nondisjunction from deeper neuroectodermal elements during the migration and maturation of these primordial tissues. The general pattern of distribution of these lesions along the lines of embryologic fusion supports this hypothesis.
This disturbance may result in the formation of a simple cyst or a continuous tract with extension to a dural or even intradural location. These dermal inclusion tracts show a greater propensity for the neural axis closure line, most commonly at the lumbosacral region and posterior cranial fossa in the midline. The fronto-nasal region is less commonly implicated but is also notable for penetrating dermal sinus formation.
Although most congenital inclusion dermoids in the craniofacial region are thought to develop through a common mechanism, the differential diagnosis and the risk of involvement of deeper structures varies based on anatomic location. Because of this, the classification of craniofacial space occupying lesions in the pediatric patient by site can help guide diagnostic testing and treatment decisions. Craniofacial midline lesions clearly pose a higher risk for neurologic involvement and deserve special attention. Additionally, the management of scalp and calvarial lesions must be considered separately from orbitomaxillofacial lesions based on the range of pathologic conditions that can be encountered. Useful anatomic groupings that have evolved are nasofrontoethmoidal, frontotemporal, orbital, and calvarial lesions.
The characterization of the risk of involvement of structures deep to the craniofacial skeleton is also required to develop a proper treatment plan. Simple dermoids have a clearly intact skeletal barrier between the lesion and deeper structures (eg, dura or orbit). Complex lesions will demonstrate features of a tract or cyst that penetrate or are likely to penetrate underlying bone or cartilage. Importantly, diagnostic imaging will not always provide a definitive picture of depth but can serve to provide information that may suggest extension or penetration. Surgical exploration is required to fully define a lesion's relationship to the surrounding structures. It follows that within each anatomic location, lesions may be subclassified as simple or complex relative to their risk of extension into deeper structures.
Evaluation and treatment
Frontotemporal and Orbital Lesions
The dermoid cyst is the most common locally palpable periorbital lesion in children with more than half of all craniofacial dermoids found in this area. The superotemporal quadrant associated with the zygomaticofrontal suture is the site most frequently involved.
Brow cysts in the frontotemporal region with easily palpable borders and no skin involvement are generally considered uncomplicated. The treatment must consider a differential diagnosis that includes epidermal inclusion cyst, lipoma, neurofibroma, benign adnexal tumor, or teratoma. If the depth of involvement or character is unclear, ultrasound evaluation has been shown to be diagnostic in the craniofacial region for dermoids ( Fig. 2 ).
Although some reports suggest imaging and then observation without excision may allow for some of these simple cysts to spontaneously involute, the definitive treatment remains excision. The excision is most often performed through a lateral brow or upper-lid blepharoplasty approach. ( Fig. 3 ) The deep surface of the dermoid lesion is often adherent at the suture, and the inclusion of the periosteum with the cyst is recommended to facilitate delivery. Every effort should be made to deliver the lesion unruptured to decrease the risk of incomplete removal and subsequent recurrence as well as to limit the inflammatory response associated with the spillage of the cyst contents into the surrounding tissues.
Endoscopic techniques have been used to hide the access scar in the hairline; however, limitations include longer operating time and difficulty recontouring any potential soft tissue depressions caused by lesion removal. The direct approaches remain simple, rapid, and cosmetic. Excision is expected to be curative when the lesion is completely removed.
Frontotemporal and orbital lesions harbor the potential for complex features with orbital or even transcranial involvement. In fact, Sathananthan and colleagues reported a high incidence of radiographic extension into or through bone around the orbit despite limited clinical indications of such. Concern for deeper involvement may come from a lesion that has borders difficult to palpate, is immobile and firmly adherent to the underlying facial skeleton, exhibits a draining fistula, or results in proptosis. When clinical features or ultrasound evaluation suggest deeper involvement, fine-cut axial and coronal orbital computed tomography (CT) greatly improves the diagnostic yield and is mandatory for surgical planning ( Fig. 4 ).
Orbital lesions may exist as bilobed dumbbell lesions with intraorbital and extraorbital components connected through the medial or lateral orbital wall. The goal remains complete excision, which may require incision of the orbital septum with intraorbital exploration. Another approach involves posterior subperiosteal dissection into the orbit followed by incision of the periosteum to deliver the cyst. For larger or posterior lesions, a lateral orbitotomy may be necessary for access and complete cyst removal. Orbital dermoids may also be of conjunctival origin. These occur more commonly in a superonasal orientation, and excision can be performed through either a conjunctival or cutaneous lid approach.
Craniofacial dermal sinuses with deep extension in the frontotemporal region occurring away from the midline are extremely rare, with less than a dozen cases reported previously. When a frontotemporal lesion demonstrates CT evidence of transcranial extension, magnetic resonance imaging (MRI) is useful to further characterize the relationship to the dura. Combined neurosurgical and craniofacial approach via a coronal flap and craniotomy may be necessary to provide wide exposure to allow for safe excision and prevent neurologic sequela. Depending on the depth of invasion, a portion of the dura may be excised, which requires primary repair or a patch. Given the rarity of reported cases, the surgical approach needs to be tailored to the clinical presentation ( Fig. 5 ).