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R. NICKBRYANMDS. JAMESZINREICHMD
Epidermoids are ectoderm-lined (squamous epithelium) inclusion cysts that arise from trapped pouches of ectoderm near normal folds or from failure of surface ectoderm to separate from the neural tube during normal embryological development between 3 and 5 weeks' gestation. They can also occur as a result of traumatic implantations that force skin tissue to be trapped in the subcutaneous tissue (eg, iatrogenic, stab, or puncture wounds).1
Epidermal inclusion cysts are usually unilocular and slowly increase in size by accumulating debris that is mostly composed of the proteinaceous material keratin and lipids from the breakdown of epithelial cell membranes. Although they can occur anywhere in the body, they present more commonly in the orbit, the calvarial diploic space, and intracranially in the middle and posterior fossae. They rarely occur in the head and neck, where they are usually located in the submental area.1,2 About 1% of these cysts occur in the oral cavity.3
Epidermal cysts are usually diagnosed during the third and fourth decades of life and show a slight male predilection. Most remain asymptomatic because of their location and small size. Nevertheless, they can occasionally become quite extensive and cause a severe mass effect on surrounding structures. When they occur intracranially, they can rupture and induce a chemical meningitis. It has been reported that epidermoids can rarely undergo malignant transformation to squamous cell carcinoma.4
Magnetic resonance imaging is the study of choice for diagnosis. Sagittal T1-weighted images of our patient's neck revealed a large heterogeneous mass measuring approximately 10 cm in diameter at the sublingual space and characterized by isointensity to hypointensity with multiple well-defined spherical areas of hyperintensity (Figure 1, arrowheads). Fast spin-echo axial T1-weighted images using a fat suppression technique demonstrated an ovoid mass in the right sublingual space with high signal intensity and numerous hyperintense nodules (Figure 2, arrows). A coronal, fast, spin-echo, T2-weighted image showed hypersignal intensity (Figure 3, double arrow) with mass effect on the airway.
These findings along with the presentation strongly support the diagnosis of epidermal inclusion cyst in this case. Epidermoids have been reported in the literature to show low signal intensity on T1-weighted images (Figure 1) and high signal intensity on T2-weighted images (Figure 3).5 The isointense to hypointense background found in the T1-weighted images was most likely the result of inner dense keratin debris,6 while the multiple areas of hyperintensity were probably caused by the cholesterol crystals.
The differential diagnosis in this case includes epidermoids, dermoid cysts, ranulas, and ganglionic cysts. Among these, ganglionic cysts, ranulas, and epidermoids usually show a low intensity signal on T1-weighted images and a high signal intensity on T2-weighted images. Dermoid cysts usually show heterogeneous signal intensity on both T1- and T2-weighted images. Ranulas are typically homogeneous lesions situated along the sublingual space. The fact that ganglionic cysts are usually found attached to a tendon sheath strongly suggested that the mass in the present case was an epidermal cyst, because no such attachment to the tendon was seen on magnetic resonance imaging scans.
The treatment of choice of epidermal cysts is surgical excision for large or symptomatic masses. Our patient underwent surgery, and an 8.0 × 5.5 × 4.0-cm, well-encapsulated, cystic, tan-white mass was excised (Figure 4) and identified as an epidermoid cyst on histopathologic examination.
Diagnosis Radiology Quiz. Arch Otolaryngol Head Neck Surg. 2002;128(6):724. doi:
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