The orbit

Unlike the eye in which most parts are amenable to direct visualization, evaluation of the orbit often requires the use of diagnosic tools such as CT scans and MRI.

Computed tomography (CT) scans are usually the radiologic technique of choice to evaluate orbital diseases such as fracture, foreign bodies, thyroid disease (Fig. 1.2) and sinusitis (Figs 5.3–5.5; 5.8).

CT scanning has made amazing contributions to medical diagnosis, but is a large contributor to the six-fold increase in diagnostic radiation in the last 30 years, because of overutilization. It is predicted that CT scans may be responsible for 1.5–2.0% of all future cancers in the US and studies reveal that patients are not informed of this risk 90–95% of the time.

Sinusitis

The orbit is surrounded on four sides by the paranasal sinuses, i.e., maxillary, frontal, sphenoid and ethmoid. Pain described as deep, or behind the eye, is most often due to allergy or infection of these sinuses. Pressure applied to the skin overlying the inflamed frontal, maxillary, and ethmoidaI sinuses may cause tenderness (Fig. 5.3). The sphenoid sinus is behind the globe and cannot be tested in this way.

F

E

M

Fig. 5.3 One evidence of sinusitis is to elicit tendemess by palpating over the frontal (F), ethmoid (E), or maxillary (M) sinus. In this case the left maxillary sinus is involved.

Fig. 5.4 CT scan showing three typical findings of ethmoiditis. A fluid level (≠) and opacification of the air spaces (≠≠) are common in an acute process. Thickening of mucosal membrane is more typical of chronicity (≠≠≠).

Fig. 5.5 CT scan of sphenoidal sinusitis with air-fluid level (≠).

Clues that may indicate disease of the orbit

A.Proptosis (exophthalmos)—forward bulging of the eye.

B.Enophthalmos—sunken eye.

C.Swollen lids (sometimes totally shut); redness and engorgement of conjunctival vessels; clear fluid under conjunctiva (chemosis).

D.Loss of eye movement (ophthalmoplegia) due to involvement of cranial nerves III, IV, and VI or local damage to extraocular muscles.

Periorbital cellulitis causes swollen lids which may be totally shut (Figs 5.7 and 5.6). This may progress to the rarer and more serious orbital cellulitis (Fig. 5.8) in which the globe may not move (ophthalmoplegia) and there is chemosis, fever, adenopathy, and exophthalmos. It is due to sinusitis 60% of the time, but also occurs with tooth, facial, or lid infections.

A tough connective tissue called the periorbita lines the inner surface of the orbit. At the orbital rim, it becomes the orbital septum which then thickens to become the tarsal plate of the lid (see Fig. 5.1). This continuous fibrous membrane acts as a barrier protecting the orbit from lid and sinus infections and might be considered an ‘orbital firewall’.

Fig. 5.7 Orbital cellulitis with chemosis and ophthalmoplegia, causing inability to look up.

Fig. 5.8 CT scan of orbital cellulitis (≠) caused by ethmoid sinusitis (≠≠). Courtesy of Rand Kirtland, MD.

Beware of the rare breakthrough. If orbital cellulitis occurs, it can easily spread to the cavernous sinus through the superior and inferior ophthalmic veins that drain the orbit and part of the face. This could cause thrombosis and death. Hospitalize the patient and treat with systemic antibiotics.

Exophthalmos

Exophthalmos (proptosis) is a protrusion of the eyeball caused by an increase in orbital contents. It is measured with an exophthalmometer (Fig. 5.10). In adults, unilateral and bilateral cases are most often due to thyroid disease. In children, unilateral cases are most often due to orbital cellulitis. Other causes are metastatic tumors, orbital hemorrhage, cavernous sinus thrombosis or fistulas, sinus mucoceles, or the following primary orbital tumors:

1hemangioma;

2rhabdomyosarcoma;

3pseudotumor (Fig. 5.9);

4lipoma;

5dermoid;

6lacrimal gland tumor (Fig. 6.131);

7glioma of the optic nerve;

8lymphoma (Fig. 5.11);

9meningioma.

Fig. 5.10 Exophthalmometer.

Fig. 5.11 CT scan of orbital lymphoma. Courtesy of Pfizer Pharmaceuticals.