Nasal dermoids (or nasal dermoid sinus cysts) are the most common congenital midline nasal lesion typically presenting in early childhood.
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Epidemiology
Nasal dermoids are rare and account for only 4-12% of all dermoid cysts of the head and neck, far less common than angular dermoids 1,2. They are, however, the most common congenital midline nasal lesions responsible for 61% of all such cases 2. There is a slight male predilection 1,2.
Additional congenital abnormalities are commonly encountered (40%) many of them related to the face. These include 2:
Other non-facial anomalies are encountered, including a variety of cardiac, central nervous system, gastrointestinal, and urogenital anomalies 2.
Clinical presentation
The vast majority of nasal dermoids present during the first 3 years of life, although occasionally they go undetected until adulthood 1,2. This is particularly the case when they do not have a superficial component.
Altough nasal dermoid can located anwhere from the subcutanous tissues of the nose to the anterior cranial fossa, the majority are confined to superficial to the nasal bones, presenting as a midline lump anywhere from the glabella superiorly to the base of the columella 1. These lesions does not enlarge with a rise in intracranial pressure (Furstenberg sign negative) 1,2. Sometimes an opening is present, froming a sinus, out of which sebacious secretions may seep or, less frequently, hair protrude 1,2.
In a minority of cases, up to 45%, the lesion has a tract that extends to the foramen cecum of the anterior cranial fossa 1.
Although local infection of these sinues is common, extension of the infection to the intracranial compartment, even when a deep component is present, is uncommon 1,2.
Embryology
During the development of the midface a diverticulum of dura protrudes down from the foramen cecum, anterior to the crista galli, all the way down to the skin of the nose 1,2. This occurs during the eigth and ninth week of gestation 3. Normally this diverticulum is transient and fully involutes, but occasionally when this occurs skin cells are pulled back along its tract. If the tract otherwise obliterates, these cells result in the formation of cysts filled with sebaceous material, hair and desquamated skin cells. Alternatively, a sinus may persist allowing this material to escape 1,2.
Pathology
A dermoid cyst is an ectodermal inclusion cyst containing skin and skin appendages; sebaceous glands, hair follicles, and occasionally sweat glands 1,2. If a cyst only contains squamous epithelium, then the term nasal epidermoid, or epidermoid inclusion cyst should be used 2.
Radiographic features
Failure to image individuals with clinical nasal dermoids risks overlooking a deeper component that can then be left untreated and potentially present later in life. CT and MRI are complimentary. The former able to give excellent bony detail. The latter fully imaging the cyst itself and allowing for confident differentiation from other alternative diagnoses 1-4.
CT
Although soft tissue reconstructions can be useful in showing the mixed attenuation (ranging from fat to calcium) typical of dermoid cysts, bony anatomy is most helpful. The presence of an enlarged foramen cecum or bifid crista galli suggest intracranial extension 2.
MRI
Nasal dermoid cysts have have the same signal characeristics as intracranial dermoid cysts, with components that demonstrate fatty signal and others more reminescent of epidermoid cysts. Presence of hair will make the signal even more heterogeneous.
There should be no solid contrast enhancement 1.
Treatment and prognosis
Surgical excision of the entire lesion is curative 1,2. The approach will vary depending on the location and extent of the lesion and may require intracranial intervention 1-4.
Incomplete excision, for example with curretage or drainage, has a high rate of recurrence 1-3.
Differential diagnosis
The differential is primarily that of other midline nasal region lesions, including:
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