Infection and severe inflammation of intraorbital tissues may lead to tissue necrosis, accumulation of pathogens, cell debris and inflammatory cells in the form of an orbital abscess.
Proptosis and eccentric displacement of the eye globe are probably the most striking symptoms of an intraorbital abscess, but swelling of the eyelids and conjunctival chemosis are also present. Erythema of the periorbital skin is common. Most patients claim local pain and visual impairment. Additionally, unspecific symptoms like malaise and fever may be experienced. Symptom onset is generally acute.
An ophthalmologic examination usually reveals internal and external ophthalmoplegia, relative afferent pupillary defect, and, with regards to the ocular fundus, venous engorgement, papilledema and possibly optic neuritis.
Symptoms may not significantly differ between distinct stages of intraorbital infections, but higher categories are generally related to more severe symptoms. Although a definitive distinction between higher category intraorbital infections is not possible without applying diagnostic imaging, the occurrence of the orbital apex syndrome has been suggested to strongly support a tentative diagnosis of subperiosteal abscess or OA. A patient diagnosed with orbital apex syndrome presents proptosis, eyelid edema, ophthalmoplegia, optic neuritis and sensory deficits arising from dysfunction of the ophthalmic branch of the trigeminal nerve [5].
If queried accordingly, most OA patients report recent infection of the upper respiratory tract, odontogenic infections or having undergone dental procedures. Both anamnestic information and clinical presentation consistent with an intraorbital abscess should prompt computed tomography imaging of the head. Ultrasonography and plain radiography are less sensitive techniques in OA diagnosis but may be applied during follow-ups if the localization of the abscess permits their application.
In images obtained by computed tomography, both ocular globes, optic nerves and ocular musculature an easily identifiable, hyperdense structures surrounded by hypodense orbital fat. An OA corresponds to a more or less homogeneous region within the orbit that generally shows a contrast-enhanced rim. Fluids or gas may be observed in the orbit. Computed tomography also allows for visualization of sinusitis, other primary diseases and/or complications like cavernous sinus thrombosis. Magnetic resonance imaging has been recommended for evaluation of intracranial complications, too [9].
With regards to the choice of antibiotic treatment, the selected drug should be effective against Staphylococcus spp, Streptococcus spp. and Gram-negative pathogens like Haemophilus spp. Treatment should be initialized immediately; results of bacterial culture should not be awaited. The material obtained after abscess drainage should, however, be utilized for bacterial culture. This measure is of importance in the case of treatment failure and in order to support future decisions regarding empiric antibiotic treatment of orbital infections. Unfortunately, isolation of the causative pathogen is not always successful, particularly if the patient has already been administered antibiotics before sampling.
Both drug therapy and surgery may be considered for OA treatment. There is no general consensus regarding criteria for either therapeutic approach and some experts recommend to drain every OA that can be recognized on computed tomography images. In any case, certain conditions indicate the need for emergency drainage of the abscess [10]:
Of note, ophthalmologic examination of pediatric patients may not yield reliable results. If doubts remain regarding the severity of the lesion, drainage is preferred over medication. In general, surgery aims at relieving intraorbital pressure and gaining specimens for bacteriological culture. Patients who undergo surgery for OA need to be administered antibiotics, too.
If the decision for primary drug therapy is taken, fluoroquinolones should be administered. According to retrospective studies, these antibiotics show very good effectivity against the most common causative agents of OA [3]. This therapy may be adjusted if the patient responds poorly. Combined antibiotic therapy may be required if the infection is caused by methicillin-resistant Staphylococcus aureus.
Bacterial infection, inflammation, and abscess formation within the orbit is a severe disease that has long since been associated with high morbidity. If adequate treatment is not provided in a timely manner, the risk of permanent visual impairment or blindness remains high. Intracranial complications such as cavernous sinus thrombosis are potentially life-threatening [8]. Nowadays, early diagnosis and proper therapy allow for complete recovery in the vast majority of patients, though.
As has been indicated above, direct inoculation of pathogens into intraorbital tissues may provoke a primary OA, the spread of infections from neighboring tissues or via blood vessels may lead to the formation of a secondary OA. In detail, the following events may eventually cause an OA:
With regards to secondary OA, other sources of infection are conceivable and basically, any bacterial infection developing in close proximity to the eye cavity may eventually provoke the formation of an OA. By far the most common cause of secondary OA is sinusitis; in turn, the likelihood for a sinusitis patient to develop orbital complications is low in infants and neonates [1]. Odontogenic infections rarely spread to the orbit without causing sinusitis. This emphasizes the need for close monitoring of patients who present with respiratory complaints as well as ophthalmologic and neurologic findings subsequent to dental procedures [2].
Distinct bacterial species have been isolated from OA samples and Gram-positive cocci have been found to account for the majority of cases in several studies [3] [4]. The following pathogens should be considered as possible triggers of OA:
Prevalence of OA caused by methicillin-resistant Staphylococcus aureus has been increasing over the last few years.
Isolated cases of OA due to infection with Aspergillus spp. have been reported.
OA constitute rare but severe complications of infectious diseases, mainly of upper respiratory tract infections. The latter are very common and each year, about 10% of the general population may develop sinusitis. Less than 4% of those patients will develop orbital complications, but this number still corresponds to an annual incidence of 4 per 1,000 inhabitants. Data regarding the likelihood of intraorbital abscess formation vary largely and estimates of as little as <1% of orbital infections and as much as 25% of such disorders have been published [5]. These differences may be partially explained by distinct diagnostic criteria since clinical presentation and diagnostic imaging findings don't necessarily coincide in OA patients.
OA is most commonly diagnosed in pediatric patients; no predilection regarding race or gender has been reported. Both the left and right eye may be affected, but abscess formation is usually unilateral.
According to Chandler et al. [6], infections of intraorbital tissues may be classified into five categories:
Single categories may either be considered as individual entities or as different stages of an intraorbital infection. However, categories 1 to 3 are not necessarily observable in a patient who will develop an OA, and neither does every orbital cellulitis turn into an abscess. Nevertheless, the sequence of pathophysiological events leading to an OA (and complicating it further) may be well illustrated following categories 1 to 5.
During preseptal cellulitis, tissue inflammation is restricted to periorbital structures. Most commonly, the periorbital skin and the eyelids are visibly swollen and tender. Infection and inflammation may spread to intraorbital tissues, resulting in orbital cellulitis. Patients may now claim an aggravation of pain and visual impairment. Proptosis and chemosis start to develop and histopathological analysis of tissue samples reveals diffuse edema and infiltration with inflammatory cells. Further spread beneath the periosteum of any cranial bone forming part of the orbit may then lead to the formation of a subperiosteal abscess. It has been estimated that about one-fourth of patients who present with orbital cellulitis may eventually develop a subperiosteal abscess [7]. This disease is usually associated with considerable proptosis and ophthalmoplegia, whereby the latter results from the mechanical hindrance of ocular muscle function or from compression of nerves passing through the superior orbital fissure. These symptoms aggravate when the patient is developing an OA, i.e., a discrete accumulation of pus within the orbit. Papilledema and characteristic alterations of the ocular fundus become visible.
An OA may complicate further if bacteria spread through the hematogenous route to the cavernous sinus and cause inflammation and/or thrombosis of the dural venous sinus.
Only general recommendations regarding prevention and adequate treatment of infections that may lead to orbital complications can be given. This applies particularly to prophylaxis of sinusitis. In this context, maintenance of a healthy, balanced diet, as well as regular exercise, are of great importance. Situations predisposing for catching a cold, e.g., exposure to cold weather while wearing damp clothes, should be avoided.
Infectious diseases possibly provoking orbital complications should be adequately treated. Close monitoring is recommended for patients diagnosed with preseptal or orbital cellulitis.
Etiology and pathogenesis of an orbital abscess (OA) differ little from other types of abscesses. The cause of an OA is a bacterial infection, whereby both Gram-positive and Gram-negative pathogens have been isolated from tissue samples. Bacteria may be inoculated directly - and thus provoke the formation of a primary OA, or infections of adjacent tissues may spread to intraorbital structures and cause a secondary OA. Hematogenous spread of pathogens to intraorbital tissues is also possible. Despite the long list of infections, most commonly sinusitis, odontogenic infection, dacryoadenitis or thrombophlebitis lead to the development of an orbital abscess.
Independent of the way pathogens take into the orbit, an uncomplicated bacterial infection does not turn into a necrotizing process without intermediate stages being passed through. In detail, most OA is preceded by orbital cellulitis and a subperiosteal abscess of the orbit. These entities differ in the extent of tissue damage, clinical presentation and prognosis from an OA. The sooner an intraorbital infection is detected, the better the outcome.
Patients suffering from an OA present with periorbital swelling that may reach grotesque dimensions. Proptosis, chemosis, ophthalmoplegia and visual impairment are some of the other common symptoms. Symptom onset may be acute and the above described intermediate stages may be too short to be distinguished clinically. Diagnosis of an OA is based on physical examination and computed tomography scans.
During early stages of intraorbital infection, medication is usually sufficient to achieve complete recovery. In the case of an OA, antibiotic treatment needs to be combined with surgical drainage in order to retain eyesight and avoid the need for enucleation of the eye. If left untreated, OA is potentially life-threatening [1].
An abscess forms in infected, inflamed tissue and typically consists of cell debris, inflammatory cells, and bacteria. This discrete accumulation of pus is demarcated by a fibrous capsule. An abscess may form in virtually all kinds of tissues and if it develops within the eye cavity, it is referred to as orbital abscess (OA).
Although an OA may result from direct inoculation of bacteria, e.g., through traumatic lesions, it generally occurs as a severe complication of infectious diseases affecting adjacent tissues. In fact, the most common trigger of OA is sinusitis and millions of people who catch a cold develop sinusitis every year. Other causes of OA are infection and inflammation of eyelid, conjunctiva, lacrimal gland or teeth.
All these infections may spread to the eyes, cause swelling and reddening of eyelids and conjunctiva and pain. In severe cases, an abscess may form within the eye cavity. It exerts pressure on surrounding structures since they are confined to this space delimited by distinct cranial bones. Consequently, symptoms may aggravate and patients may experience vision loss. The eyeball may protrude.
These symptoms will prompt computed tomography scans of the head. In images obtained by this technique, localization and size of the abscess can be determined. Anamnestic data, clinical presentation and findings of diagnostic imaging can all be considered when deciding whether to treat the infection conservatively, i.e., with antibiotics or to drain the abscess. Early diagnosis and provision of adequate treatment are associated with a good prognosis.