MR IMAGING AND CT OF ORBITAL INFECTIONS AND COMPLICATIONS IN ACUTE RHINOSINUSITIS
Section snippets
IMAGING STRATEGIES
Orbital imaging should be considered in most patients with the acute onset of periorbital inflammation. If the inflammatory process is obviously preseptal and localized to the skin and subcutaneous areas of the eyelid, orbital imaging is unnecessary. Patients with clinical signs suggesting postseptal involvement, however, including visual acuity less than 20/40, proptosis, chemosis, or limitation of ocular motility should be studied. In addition, any patient in whom the diagnosis is uncertain,
PARAMAGNETIC CONTRAST MATERIAL AND THE USE OF FAT-SUPPRESSION TECHNIQUES
Gadolinium enhancement is extremely useful in the diagnosis of certain orbital pathology including orbital infections.29, 31, 35 With fat-suppression techniques, the T1-weighted MR images demonstrate marked expansion of gray scale with apparent increased intensity of the extraocular muscles and lacrimal glands. Therefore, pregadolinium (with or without fat suppression) and postgadolinium fat suppression T1-weighted MR images are very useful to evaluate the presence of the degree of enhancement.
ANATOMY OF PARAORBITAL SINUSES
Between 60% and 80% of inflammatory diseases of the orbit originate in the sinonasal cavities.25, 39 For this reason, a thorough understanding of the embryology and anatomy of the paranasal (paraorbital) sinuses is essential in understanding the pathogenesis of orbital infections.
VENOUS DRAINAGE OF THE PARAORBITAL SINUSES
Venous drainage of the paranasal (paraorbital) sinuses consists of a system of valveless veins that interconnect the sinuses with the orbits, the cavernous sinus, and the facial tissues (see Fig. 4, Fig. 7).15, 19, 22 This freely anastomosing system allows thrombophlebitic phlebitis spread of inflammation and infection between these adjacent structures.19
The superior ophthalmic vein receives venous drainage from the frontal and ethmoid sinuses via the nasofrontal vein, the ethmoidal veins, and
PERIORBITA
The periosteum of the orbit (periorbita) is an important anatomic structure. It represents the only soft tissue barrier between the sinus and orbital contents.8 It is a tough, fibrous membrane that can be easily stripped from the bone except at the suture lines, where it passes through to fuse with the periosteum on the other side.8 The orbital septum or palpebral fascia is a reflection of the periorbita at the anterior margins of the orbit to become continuous with the tarsal plates. The
IMAGING CHARACTERISTICS OF SINUSITIS AND RELATED DISORDERS
Because the majority of cases of bacterial orbital cellulitis are associated with paranasal sinusitis, one should have a basic understanding of the imaging appearance of these disorders. CT findings in acute sinusitis include mucosal thickening; air–fluid level; enhancing pocket(s) with nonenhanced central zone (pus); or complete opacification of the involved sinus. If the disease extends beyond the mucosa, there may be bone rarefaction or erosion suggestive of osteomyelitis. In chronic
BACTERIAL ORBITAL CELLULITIS CLASSIFICATION
Orbital complications of paranasal sinusitis are relatively common in children, but are uncommon in adults. Predisposing factors for the spread of the infection to the orbit include congenital, surgical, or traumatic dehiscence in the common bony walls, the anterior and posterior ethmoid neurovascular foramina, and the valveless sinus and orbital veins and diploic veins of Breschet, which are avenues for septic thrombophlebitic spread of sinus disease to the orbit.29 Based upon the anatomy and
BACTERIAL PRESEPTAL CELLULITIS
Preseptal cellulitis describes infections limited to the skin and subcutaneous tissues of the eyelid anterior to the orbital septum. Clinically, the patient has erythema and swelling of the eyelids. There is no proptosis, chemosis, or limitation of ocular motility. It is unusual for a preseptal infection to traverse the orbital septum and result in postseptal cellulitis (Fig. 9).
Postseptal cellulitis defines an infectious process as one that occurs within the orbit proper, behind the orbital
Inflammatory Edema.
The first manifestation of orbital involvement in patients with paranasal sinusitis is the development of inflammatory edema. Contrast-enhanced study is necessary. The edematous orbital fatty reticulum and adjacent tissues demonstrate some enhancement on postcontrast CT and MR imaging scans (Fig. 10). Generally, the involvement is maximal in the extraconal fat directly adjacent to the most severely affected sinus. Although proptosis is usually present, suggesting more diffuse involvement,
SUBPERIOSTEAL ABSCESS
The next event in the course of the disease is the formation of a subperiosteal abscess (SPA) (Figs. 13 and 14). The process occurs due to spread of the infection through the congenital dehiscenses and foramina of the thin orbital bones as well as thrombophlebitic spread, although the latter is less common. Clinically, the patient has marked swelling and erythema of the eyelids, chemosis, and proptosis. Motility is limited, usually more so when ductions toward SPA are attempted, and visual loss
ORBITAL ABSCESS
The development of a true intraconal orbital abscess secondary to paranasal sinusitis or dental infection is uncommon since the advent of modern antibiotic therapy. More commonly, this occurs secondary to penetrating orbital injury; ocular surgery; or as a metastatic process (septic emboli).26 If orbital abscess is present as a sequela to paranasal sinusitis, progression to this stage can usually be linked to delay in diagnosis and therapy, or an immunocompromised state. Clinically, patients
CAVERNOUS SINUS THROMBOSIS
Cavernous sinus thrombosis results from the spread of infections of sinonasal cavities, orbit, and from infection of the middle third of the face.2, 3 Cavernous sinus thrombosis originates from a septic thrombophlebitis arising in the ophthalmic veins (Fig. 19).2 Proptosis and ophthalmoplegia are common. Offending organisms may be aerobic or anaerobic, with Staphylococcus aureus and anaerobic streptococci being the most common organisms.13 Clinically, patients with cavernous sinus thrombosis
FUNGAL ORBITAL CELLULITIS
Orbital fungal inflammations are often seen in patients with a history of uncontrolled diabetes mellitus and immunocompromised patients, such as those with AIDS. AIDS, caused by infection with HIV, produces profound derangement of the host's immune system. Immunologic abnormalities in AIDS patients include defective cell-mediated immunity with T-cell lymphopenia, functional defect of CD4+ T cells, inadequate antigen-specific antibody response to new antigenic stimuli due to B-cell dysfunction,
DIFFERENTIAL DIAGNOSIS
The differential diagnosis of orbital cellulitis is extensive and includes the following:
Inflammatory and allergic
Idiopathic orbital inflammation
Mucocele
Wegener's granulomatosis
Angioneurotic edema
Congenital
Dermoid cyst
Encephalocele
Infantile cortical hyperostosis
Vascular
Cavernous sinus thrombosis
Cavernous sinus fistula
Leukemia
Hemophilia (orbital hemorrhage)
Traumatic
Laceration and hemorrhage of the orbit
Orbital wall fracture with orbital hemorrhage
ACKNOWLEDGMENT
The authors express sincere appreciation to Dale Peal and Margie Yates for their secretarial assistance.
References (56)
- et al.
Septic cavernous sinus thrombosis following infection of ethmoidal and maxillary sinuses: A case report
Int J Pediatr Otorhinolarygol
(1994) - et al.
Orbital apex syndrome
Surv Ophthalmol
(1987) - et al.
Diagnosis and treatment of intracranial complications of paranasal sinus infection
J Oral Maxillofac Surg
(1995) Subperiosteal abscess of the orbit: Age as a factor in the bacteriology and response to treatment
Ophthalmology
(1994)- et al.
Orbital abscess
Surv Ophthalmol
(1984) - et al.
Orbital space-occupying lesions: Role of computed tomography and magnetic resonance imaging: An analysis of 145 cases
Radiol Clin North Am
(1987) - et al.
Normal CT anatomy of the paranasal sinuses
Radiol Clin North Am
(1984) - et al.
MRI of the paranasal sinuses and nasal cavity
Radiol Clin North Am
(1989) - et al.
Chronic inflammatory sinonasal diseases including fungal infections: The role of imaging
Radiol Clin North Am
(1993) - et al.
MR imaging in rhinocerebral and intracranial mucormycosis with CT and pathologic correlation
Magn Reson Imaging
(1992)
Inflammatory disorders of the paraorbital sinuses and their complications
Radiol Clin North Am
Superior ophthalmic vein thrombosis complication of ethmoidal rhinosinusitis
Arch Otolaryngol Head Neck Surg
Intracranial complications of sinus disease
Trans Am Acad Ophthalmol Otolaryngol
Blindness resulting from orbital complications of sinusitis
Otolaryngol Head Neck Surg
Microbiology of subperiosteal orbital abscess and associated maxillary sinusitis
Laryngoscope
Computerized tomographic detection of sinusitis responsible for intracranial and extracranial infections
Radiology
Orbital and intracranial complications of sinusitis
CT scanning in rhinocerebral mucormycosis and aspergillosis
Radiology
The pathogenesis of orbital complications in acute sinusitis
Laryngoscope
Orbital ultrasonography
Subdural empyema secondary to purulent frontal sinusitis
Arch Otolaryngol Head Neck Surg
Staging of orbital cellulitis in children
J Pediatr Ophthalmol Stabismus
Infections of the orbit
The role of high resolution computerized tomography and standardized ultrasound in the evaluation of orbital cellulitis
Laryngoscope
Anatomy
Computerized tomography and ultrasound in the evaluation of orbital infection and pseudotumor
Radiology
Subperiosteal abscess of the orbit
Arch Ophthalmol
Subperiosteal inflammation of the orbit: A bacteriological analysis of 17 cases
Arch Ophthalmol
Cited by (0)
Address reprint requests to H. Sprague Eustis, MD, Ochsner Clinic, 1514 Jefferson Highway, New Orleans, LA 70121