Epidermal inclusion cysts are rare tumors that occur from the inclusion of epidermal elements into the dermis after trauma. 1 These cysts have a predilection for the highly traumatized sites of the body like fingers, soles and palms. 2 Epidermal inclusion cysts have also been described in various other regions and in tissues deeper than the dermis. In the English literature, two cases of epidermal inclusion cyst were described that involved the infratemporal fossa with extension into the infratemporal region after surgery to the area. 3 We present a case of epidermal inclusion cyst of the deep infratemporal fossa after blunt trauma to the temporal region.
A 41-year-old otherwise healthy man presented with a complaint of a soft-tissue mass in the left temporal region. The mass was painless and had been enlarging steadily for the past 5 years. On physical examination, a 7 × 4-cm soft-tissue mass was noted lateral to the lateral canthus, extending into the temporal hairline above the auricular sulcus (Fig A). It appeared to be fixed above the zygoma. The mass was nontender, noncompressible, and nonpulsatile, and was exacerbated by masseter excursion. The cranial fifth and seventh nerves were intact. The patient had a past medical history of blunt trauma to the left temporal area by a drive shaft 12 years previously. At the time of injury, he did not sustain any open wounds, and was treated conservatively as an outpatient.
Computed tomography of the head demonstrated a 6 × 1.5 × 4.5-cm soft-tissue mass in the infratemporal fossa (Fig B). The tumor extended superiorly to the temporal line, deep to the temporalis muscle.
The temporal region was accessed using a T incision. Dissection was carried deep to the superficial temporal fascia to preserve the facial nerve. The mass was noted to be deep to the deep layer of the temporal fascia. During surgery, the sebaceous contents of the tumor appeared on the superior border of the tumor. The tumor was found to extend infratemporally and deep within the infratemporal fossa under the zygoma (Fig C). The tumor was removed circumferentially en bloc.
On gross pathological examination, the tumor appeared to be a 6.5 × 3.5 × 2.0-cm partially lobulated, cystic lesion containing brown cheeselike material (Fig D). The cystic wall was less than 0.1 cm in thickness. Microscopic evaluation revealed an epidermal cyst (Fig E). There was no giant cell foreign body reaction.
Epidermoid cysts can be either congenital or acquired. The congenital ones develop during the fusion of the embryo when the ectodermal tissue gets trapped in the line of fusion. 2,4 These arise from epithelial cells displaced between the third and fifth week of fetal development. 5 The acquired cysts, which are known as epidermal inclusion cysts, arise from inclusion of epidermal structures in the dermis and other deeper tissues after trauma. 2,4,6 Epidermal inclusion cyst and traumatic epidermoid cyst are synonyms, and indicate a traumatic etiology. 6 The trapped epidermis acts like a skin graft, becomes independent, and continues to grow in its new location producing keratin and forming a cyst. The most commonly accepted pathogenesis is the “epithelium implant theory,” which suggests that the epidermal cells are driven into deeper tissues with an injury from a blunt instrument. 2 The injury to the epithelium may be a blunt or penetrating trauma, lumbar puncture, needle biopsy, or even a surgical procedure.
Small fragments of residual epidermis have been demonstrated on the lumen of the injection and biopsy needles. 7,8 The tip of the needle tears small fragments of epidermis and carries it to the deeper structures. Spinal canal epidermal cysts are rare and have been described after lumbar puncture. 9–11 Needle aspiration biopsies of the breast have also resulted in epidermal inclusion cysts of the breast, which can be mistaken as cancer. 7 Utilization of special needles with stylets can prevent this condition. 12 Multiple stab wounds are also discouraged because they increase the chance of epidermal inclusion cysts. 7
Surgery can also be a causative factor in the development epidermal inclusion cysts at various parts of the body. It can be a complication of reduction mammaplasty after incomplete deepithelialization of the dermoglandular unit, during which the epithelial elements are retained. 13 Circumcision of the clitoris, which is practiced in certain parts of Africa, has also resulted in epidermal inclusion cysts. 14 They have been reported in the upper neck after radical mastoidectomy, 15 in the parotid region after temporalis fascia harvest, 5 in the nasal bridge after rhinoplasty, 16 and in the deep infratemporal fossa after harvest of temporal fascia and after facial nerve decompression. 3
A large majority of posttraumatic cysts that are not associated with surgery or needle biopsy occur on the hands and feet, mostly in the fingers, toes, palms, and soles. This is not a coincidence, because the hands and feet are the most traumatized areas of the body. The distal phalanges are involved more than the proximal regions of the hands and feet. 17 Men are affected more than women because they exhibit a greater incidence of trauma. 18,19 The trauma can be blunt or penetrating, and the location of the tumor can vary from the dermis 20 to deeper structures. Epidermal inclusion cysts have been described in the fingers 12 years after a laceration, 21 and after crush injury to the thumb. 22 They have been found in the subungual regions of the fingers and toes. 23 A very rare location is intratendinous. In 1 patient the tumor was found to be embedded deeply in the fascicles of the flexor digitorum profundus. 24 The cysts in the fingers may lead to bone destruction. 21 Shoe impingement has led to cyst development above the extensor hallucis longus tendon. 20 Epidermal inclusion cysts have been found on the muscular layer of the lips after blunt trauma, 4 and on the vermilion border after laceration. 2 A history of repeated trauma to the testicles was present in a patient with bilateral epidermal inclusion cysts of the testis. 25 Lee 26 described a single case of intracranial epidermal inclusion cyst 2 years after a depressed skull fracture. Our patient is unique to the English literature because he presented with an epidermal inclusion cyst of the deep infratemporal fossa after blunt trauma.
Epidermal inclusion cysts are lined with stratified squamous epithelium and lack any appendages like sweat glands or hair follicles. They contain keratinaceous material and white, cheesy, lipid-rich debris. 6 Congenital epidermal cysts have thin walls, whereas the traumatic cysts have a well-formed granular layer. 6 Younger cysts tend to have all the epidermal layers, and become thinned out and atrophic once the cyst gets old, and are filled with keratinaceous material. 27 Rupture of cyst contents leads to a granulomatous foreign body reaction, 24,27,28 which is painful and may be mistaken as infection of the cyst. 6 Occasionally the cyst connects to the skin surface via keratin-filled pores. Calcification of the cyst wall has occasionally been reported. 3 Epidermal cysts unlike dermoid cysts do not contain ectodermal appendages like hair, nerve, bone, teeth, and sweat glands. 29
Typically, the history given by patients suggests that trauma is the etiology for the inclusion cyst. The time from injury to occurrence of symptoms can be as long as 20 years (12 years in our patient) to as short as 6 months. 2,23 The size of the lesion depends on the time of growth and its related location in the body. These are slow-growing cysts, but they sometimes suddenly enlarge because of an increased rate of desquamation of the epithelium. On the fingers and toes, small cysts may become symptomatic because of the nature of the surrounding tissue with limited expansion. In the infratemporal fossa there is less resistance for expansion and more room for enlargement, allowing the tumor to become larger, and thus it is not recognized until a later time. 3 Clinically these cysts present as painless, slow-growing, well-circumscribed swellings. 2 Symptoms may vary depending on the location of the tumor and the pressure on the surrounding structures. Cysts in the brain parenchyma may first present with seizures. 26 If the cyst ruptures, the keratinaceous contents may incite an inflammatory foreign body reaction that causes pain and could be mistaken for infection of the cyst. 6,24,28 The treatment is excision of the cyst, including the attached skin containing the pore. Incomplete excision of the cyst results in local recurrence. An inflamed cyst should be allowed to heal before surgery is performed.
Trauma is the precipitating factor in the etiology of epidermal inclusion cysts. Epithelial cells are driven into the dermis and into deeper tissues, where they continue to proliferate and form a cyst. We presented a case of epidermal inclusion cyst of the deep infratemporal fossa that was evident 12 after the patient sustained blunt trauma to this region. This case is the only epidermal inclusion cyst found in the deep infratemporal fossa after blunt trauma.
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