Orbital Dermoid

Findings

Figure 1 and Figure 2: Ovoid well-circumscribed ventromedial left orbital extraconal mass resulting in mass effect on the intraorbital contents displacing the globe laterally, demonstrating nonaggressive features. Internal areas of fat attenuation.

Figure 3and Figure 4: Ovoid well-circumscribed mass centered in the post-septal, extraconal left orbit which exerts mass effect on the left globe, displacing it laterally. Signal characteristics of the lesion are most consistent with an intraorbital dermoid, including fat signal layering within the nondependent portion of this predominantly cystic lesion. This fat floats on underlying proteinacous cystic material.


Diagnosis: Orbital Dermoid


Patients with this diagnosis generally complain of an orbital mass, which may be visible on physical examination. Growth of these lesions is generally slow. In adults, dermoids may become symptomatic for the first time and grow considerably over a year. Based on this fact, some authors have concluded that these lesions may be dormant for many years and/or have intermittent growth, such as in our case example.

Dermoids are the most common benign congenital lesion of the orbit, accounting for 1-2% of all orbital masses. Dermoid and epidermoid cysts are examples of choristomas, tumors that originate from aberrant primordial tissue. These tumors contain normal-appearing tissue in an abnormal location. As two suture lines of the skull close during embryonic development, dermal or epidermal elements are pinched off and form cysts, which are adjacent to the suture line. Approximately 50% of these tumors that involve the head are found in or adjacent to the orbit. They arise most often in the superolateral portion of the orbit at the frontozygomatic suture. They can also arise inferiorly, posteriorly, or medially (as in our case example). These lesions are extraconal and displace the globe. If the displacement is great, interference with vision by compression of the optic nerve may result or ocular motility may be disturbed, typically resulting in diplopia.

On MR the diagnosis is usually clinched with high signal on T1WI in the region which suppresses with fat saturation techniques. Fat may be seen floating in cystic fluid on T1WI.

These tumors are most often noted in young children; however, they may appear or grow at any age. In adults, they are more likely to displace the globe, possibly growing or eroding their way into adjacent