Introduction
There are various forms of orbital infection, including those listed in the Jain-Rubin classification:
- 1.
Periorbital cellulitis
- 2.
Orbital cellulitis with or without intracranial complications
- 3.
Orbital abscess with or without intracranial complications
- a.
Intraorbital abscess, which may arise from collection of purulent material in an orbital cellulitis
- b.
Subperiosteal abscess, which may lead to true infection of orbital soft tissues
- a.
In addition, orbital infections that are not specifically addressed by this classification include dacryocystitis, dacryoadenitis, and endophthalmitis. Some forms of orbital infection can evolve into other types, and different types can coexist.
Besides delineating the extent of infection and potential complications, it is helpful to make an attempt to identify the source of an orbital infection on imaging, since this may influence treatment. In addition to patient history, the constellation of imaging findings can often yield insights into how the infection arose. Orbital infections can arise from primary infection of the sinuses, skin, or teeth; septicemia; or penetrating injury.
Certain anatomic structures play a role in how infections progress. For example, the orbital septum provides a barrier against the spread of periorbital infections into the orbit proper. The orbital septum is a thin sheet of fibrous tissue that originates in the orbital periosteum and inserts in the palpebral tissues along the tarsal plates. Portions of the orbital septum can sometimes be discerned on imaging ( Figs. 37.1 and 37.2 ). The distinction between periorbital and orbital processes is clinically important because postseptal infections are treated more aggressively in order to prevent devastating complications such as cavernous sinus thrombosis and meningitis. Postseptal infections are treated more aggressively than preseptal infections due to the potential of devastating complications including optic nerve compromise and vision loss, cavernous sinus thrombosis and meningitis.
Periorbital Cellulitis
Periorbital or preseptal cellulitis is defined as inflammation limited to the soft tissues anterior to the orbital septum; it most commonly arises from the contiguous spread of infection involving adjacent structures such as the cutaneous tissues of the face, dentition, and ocular adnexa, or directly from penetrating injury. Symptoms include swelling and erythema of the eyelids, chemosis, and, in severe cases, decreased eye movement without proptosis. Cross-sectional imaging demonstrates diffuse soft-tissue thickening and fat stranding anterior to the orbital septum and can sometimes delineate the source of the infection ( Fig. 37.3 ). Periorbital cellulitis is typically treated with oral antibiotics. However, in the rare event that periorbital cellulitis leads to abscess formation, as manifested by a rim-enhancing fluid collection on cross-sectional imaging ( Fig. 37.4 ), incision and drainage may be necessary.
Orbital Cellulitis
Orbital or postseptal cellulitis is an infectious process recognized on imaging by the presence of orbital fat stranding and enhancement as well as occasionally extraocular myositis ( Fig. 37.5 ). Thus, as opposed to periorbital cellulitis, orbital cellulitis can result in proptosis. Although postseptal cellulitis can result from extension of preseptal infection, it is most commonly caused by paranasal sinusitis, which spreads to the orbit via a perivascular route. Consequently, bone destruction is usually not apparent on imaging. However, thrombophlebitis of the superior ophthalmic vein can result from orbital cellulitis and extend into the cavernous sinuses. The intravascular thrombus appears as an intravascular filling defect on contrast-enhanced studies ( Fig. 37.6 ). Treatment of orbital cellulitis typically requires intravenous administration of antibiotics. The clinical importance of recognizing and describing these findings cannot be overemphasized, as patients with orbital infections will typically require intravenous antibiotics. If there is no improvement within 24 to 48 hours, the patient will often require endoscopic sinus surgery and drainage. Patients with an already established intraorbital abscess often go to surgery for drainage right away.
Subperiosteal Abscess
Development of an orbital subperiosteal abscess is most commonly associated with sinusitis and may develop from subperiosteal phlegmon, which appears as abnormal soft tissue attenuation within the orbital fat adjacent to the bone on imaging ( Fig. 37.7 ). On the other hand, subperiosteal abscesses appear as dome-shaped fluid collections along the orbital wall, often with associated stranding of the adjacent orbital fat ( Fig. 37.8 ).
