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Mary Thomas* is an 18-year-old, developmentally delayed female who—with her family’s encouragement—had been enjoying a life that was as active and normal as possible. Her parents brought her to our clinic because they had become increasingly concerned about progressive prominence of her right eye. They told us that their daughter was otherwise a healthy individual who had never had any other ocular complaints. They also reported that she had no past history of surgery or facial trauma.
What We Saw
Ms. Thomas did not complain of any pain, decreased visual acuity or diplopia. Due to the patient’s developmental delay, our ability to obtain an accurate history from her was difficult.
However, upon further questioning, she did describe headaches, which had worsened over the previous month. Photographs that had been taken two years prior did not show evidence of any abnormalities.
On examination, her BCVA was 20/20 in both eyes. Her motility exam demonstrated a –1 elevation deficit of the right eye. Exophthalmometry measurements were 23 mm in the right eye and 17 mm in the left at a base of 92 (Fig. 1).
Further external examination revealed a fullness of the superior temporal right upper lid. A mass was palpable in this area, just under the right superior orbital rim. There was mild resistance to retropulsion of the right globe.
Slit-lamp examination and dilated exam of the posterior segment were normal in both eyes. A computed tomography scan showed a large mass in the superotemporal orbit (Fig. 2). We noted that the mass appeared to erode through the orbital roof into the intracranial space.
Characterizing the direction of proptosis and the resulting globe position can be helpful when considering the broad differential diagnosis for an orbital mass.
A mass that results in inferonasal globe displacement, like the one seen in our patient, is typically a lacrimal gland tumor, dermoid cyst or epidermoid cyst. Other, less likely, possibilities included a mucocele or an encephalocele.
After consulting with the neurosurgery service, excision of the lesion was recommended. An anterolateral craniotomy with removal of the orbital roof was performed, exposing the extent of the large tumor (Fig. 3). The mass was successfully resected en bloc and sent to pathology for evaluation. Gross description showed a 3.0- x 2.0- x 2.0-cm, tan-yellow, friable mass. Histopathology revealed classic features of an epidermoid cyst, including an epithelium-lined cyst filled with keratin, with no evidence of dermal appendages (Fig. 4).
The final diagnosis was an epidermoid cyst of the right orbit with extension into the intracranial cavity.
What’s Your Diagnosis?
|WE GET A LOOK AT THE PATIENT. This external photograph shows superotemporal fullness of the right upper lid as well as proptosis and downward displacement of the right eye (Fig. 1). On computed tomography, a coronal scan shows a homogeneous mass in the superotemporal aspect of the right orbit with invasion into the intracranial space (Fig. 2).
|TREATMENT. After anterolateral craniotomy and removal of the orbital roof was performed, a spherical, tan-yellow mass is noted. The underlying ocular adnexa is not visualized (Fig. 3). This hemotoxylin-eosin stained specimen shows an epithelium- lined cyst filled with keratin. There is no evidence of dermal appendages (Fig. 4).
Definition and incidence. Epidermoid cysts are rare lesions that comprise approximately 1 to 1.5 percent of all intracranial neoplasms.1 Although originally grouped together with the more common dermoid cysts, epidermoid cysts represent a distinct entity characterized histologically by a lining of squamous epithelium with desquamated layers of keratin without any mesodermal elements—such as hair follicles or sebaceous glands—which are characteristic of dermoid cysts.2
Pathogenesis and presentation. Epidermoid cysts can be categorized as primary (congenital) or secondary. Primary lesions most likely involve displacement of epithelial elements during closure of the neural groove or other epithelial fusion lines between the third and fifth weeks of gestation.1,2 Secondary epidermoid cysts result from posttraumatic implantation of surface epithelium.
The most common presenting sign of an orbital epidermoid cyst is unilateral proptosis. Other signs may include impairment of extraocular movements, diplopia and blurring of vision.
Several common nonhistological features also help distinguish dermoid from epidermoid tumors. First, dermoid cysts usually present in childhood or young adolescence. Epidermoid cysts present later in life because of their deep location in the orbit; they often originate in the diploë of bone and have a longer latent period.2 Second, dermoid cysts frequently appear near the midline and orbital region. The most common location for an orbital dermoid cyst is superotemporal, originating from the frontozygomatic suture. Epidermoid cysts are more commonly located laterally in the diploë of the skull (the diploic space between the skull’s inner and outer tables), fourth ventricle and cerebellopontine angle.1,3
Diagnosis and treatment. Arana and colleagues reviewed 37 cases of intradiploic epidermoid cysts and described the typical appearance in several radiologic modalities.3 On plain films, epidermoid cysts were most commonly seen as a well-defined lesion smaller than 5 cm with sclerotic borders. CT scanning allows greater assessment of bony involvement and intracranial extension, generally revealing involvement of both diploic tables and a density similar to brain parenchyma.2
On MRI, epidermoid cysts give a high signal on T2-weighted images and a variable signal on T1-weighted images. High intensity on T1-weighted images has been reported in several cases with hemorrhage into the cyst. These MRI characteristics are shared with dermoid cysts.3
Orbital epidermoid cysts are treated with complete surgical excision through anterolateral orbitotomy or a frontotemporal craniotomy for cases, like this one, with intracranial extension. Surgical indications for excision include definitive histologic diagnosis, correction of proptosis, prevention of further destruction of surrounding structures and reduction of potential for malignant transformation. Great care must be taken to completely excise the epithelial lining to prevent recurrence.1,2,4
* Patient name is fictitious
Mr. Forcina is a medical student, Dr. Wilkes is a fellow and Dr. Hildebrand is associate professor of ophthalmology. All three authors are at the University of Oklahoma Health Sciences Center.
1 Keene, J. R. et al. J Oral Maxillofac Surg 2005;63:1674–1676.
2 Eijpe, A. et al. Ophthalmology 1991;98:1737–1743.
3 Arana, E. et al. Neuroradiology 1996;38:306–311.
4 Bretschneider, T. et al. Neuroradiology 1999;41:570–572.
MORE ROUNDS. Tackle another puzzling case of proptosis: See Morning Rounds in the September 2009 issue of EyeNet at www.eyenetmagazine.org/archives.