Orbital cellulitis is an acute infectious inflammation of the soft tissues posterior to the orbital septum. It most commonly develops as a complication of ethmoid sinusitis, and the distinction between preseptal (periorbital) and postseptal (true orbital) cellulitis is critical for clinical management. Postseptal cellulitis carries the risk of progression to subperiosteal abscess, orbital abscess, cavernous sinus thrombosis, and intracranial complications. It is more common in children; Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae are the most frequent causative organisms. Urgent diagnosis and treatment are required because delays can lead to life-threatening complications such as permanent vision loss, meningitis, and cerebral abscess.
Age Range
2-50
Peak Age
10
Gender
Equal
Prevalence
Common
The pathogenesis of orbital cellulitis most commonly involves direct spread of paranasal sinus infection into the orbit. The lamina papyracea between the ethmoid sinus and orbit is a thin bony structure prone to dehiscences, allowing infection to pass into the subperiosteal space and subsequently into the orbital fat. Sinus-derived venous thrombophlebitis can cause rapid spread of infection to the cavernous sinus through the valveless ophthalmic veins. Edema, vascular congestion, and inflammatory cell infiltration resulting from the infectious process cause diffuse increased density in the orbital fat and reticular pattern infiltration; this appears as obliteration of fat planes on CT and T2 signal increase on MRI. Subperiosteal abscess formation represents a localized collection of purulent material beneath the periosteum, most commonly seen along the medial orbital wall, appearing as a crescent-shaped fluid collection on CT.
A peripherally enhancing crescent-shaped hypodense fluid collection along the medial orbital wall along the lamina papyracea is the pathognomonic finding of subperiosteal abscess developing as a complication of sinusitis. The collection is located between the periosteum and bone and may displace the globe laterally.
Diffuse increased density and reticular pattern infiltration is seen in the orbital fat. The normal hypodensity of orbital fat is lost and fat planes are obliterated. This finding is critically important in distinguishing preseptal from postseptal cellulitis; in postseptal cellulitis, infiltration in the fat posterior to the septum is prominent. Extraocular muscles may appear swollen due to surrounding inflammation. Infiltration may be homogeneous or heterogeneous; heterogeneous infiltration suggests early abscess development.
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Diffuse increased density in the orbital fat with obliteration of fat planes and reticular infiltration is noted, consistent with postseptal orbital cellulitis.
A crescent or lens-shaped hypodense fluid collection is seen along the medial orbital wall along the lamina papyracea. The collection shows peripheral ring enhancement and is located between the periosteum and bone. Subperiosteal abscess is most commonly found along the medial orbital wall (complication of ethmoid sinusitis) and less frequently along the superior orbital wall (frontal sinusitis). The abscess wall is smooth and thin; a thick and irregular wall suggests an aggressive pathogen or chronicity. The globe may be laterally displaced, and opacification of ipsilateral ethmoid sinuses typically accompanies the finding.
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A peripherally enhancing crescent-shaped subperiosteal fluid collection is noted along the medial orbital wall along the lamina papyracea, consistent with subperiosteal abscess.
Diffuse signal increase is seen in the orbital fat on T2-weighted images, and this finding becomes much more prominent on fat-suppressed (STIR or fat-sat T2) sequences. The normal intermediate-to-high T2 signal of orbital fat markedly increases due to edema and inflammation. The boundaries of infiltration are clearly evaluated on STIR sequences. Edema of extraocular muscles, perineural inflammation, and increased fluid in the optic nerve sheath may also accompany the finding. Fluid accumulation in the prescleral space (beneath Tenon's capsule) indicates posterior scleral inflammation.
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Diffuse signal increase in the orbital fat is noted on T2-weighted and STIR sequences, consistent with orbital infectious/inflammatory process.
On diffusion-weighted imaging (DWI), the abscess cavity shows marked diffusion restriction and appears hyperintense at high b-values (b=1000). Low signal on ADC map confirms true diffusion restriction. Subperiosteal abscess, orbital abscess, and intracranial complications (epidural abscess, subdural empyema) can be detected early with DWI. DWI findings are also valuable in monitoring treatment response; diffusion restriction decreases with successful treatment. Perilesional cerebritis or early abscess formation may also show high signal on DWI.
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A collection showing diffusion restriction characterized by high signal on DWI and low signal on ADC map is noted, consistent with abscess formation.
On contrast-enhanced T1-weighted images (with fat suppression), diffuse enhancement of orbital fat tissue, abnormal enhancement of extraocular muscles, and peripheral ring enhancement around the abscess are observed. In case of cavernous sinus involvement, an enlarged and enhancing cavernous sinus, filling defect (thrombosis), or irregular enhancement may be seen. Dural extension manifests as meningeal enhancement. Optic nerve sheath enhancement indicates perineural spread of infection. Fat-suppressed contrast-enhanced T1 sequence is the best sequence for evaluating enhancement and is indispensable in the evaluation of orbital inflammatory pathologies.
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Diffuse enhancement of the orbital fat tissue and peripheral ring enhancement around the abscess are noted on contrast-enhanced fat-suppressed T1-weighted sequences, consistent with active infectious/inflammatory process.
On bone window CT reformatted images, dehiscence, erosion, or destruction of the thin bony structure of the lamina papyracea may be observed. The lamina papyracea is a very thin bony structure (0.2-0.5 mm) forming the medial orbital wall, and congenital dehiscences are common. In the infectious process, bone erosion, osteomyelitis findings, and bone destruction may be seen. Opacification, air-fluid levels, and mucosal thickening in ipsilateral ethmoid cells are identified as the infectious source. Evaluation of frontal, maxillary, and sphenoid sinuses is also important because multisinus involvement indicates a more aggressive infection.
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Focal dehiscence/erosion of the lamina papyracea is noted on bone window images, accompanied by opacification of ipsilateral ethmoid sinuses, consistent with sinus-related orbital infection.
B-mode ultrasonography shows soft tissue swelling and edema in the preseptal region. Thickening and echogenicity change in the eyelid and periorbital soft tissues are seen. In postseptal cellulitis, increased echogenicity of orbital fat and heterogeneous appearance in the retrobulbar area may be observed. In the case of subperiosteal abscess, an anechoic or hypoechoic collection adjacent to the medial orbital wall may be detected; however, ultrasonography is limited compared to CT and MRI for evaluating structures posterior to the lamina papyracea. The greatest advantage of ultrasonography is its ability to perform rapid bedside assessment and to aid in preseptal-postseptal differentiation, especially in children, without radiation exposure.
Report Sentence
Prominent soft tissue swelling and edema in the preseptal region is noted on B-mode ultrasonography, consistent with orbital cellulitis.
Criteria
Infection remains confined anterior to the orbital septum. Eyelid edema and erythema are present but proptosis, chemosis, and restriction of eye movements are absent. CT shows preseptal soft tissue swelling but no infiltration in postseptal orbital fat.
Distinct Features
Orbital septum is intact and normal fat planes are preserved posterior to it. Extraocular muscles are normal. Usually rapid response to intravenous antibiotic therapy. CT indication is limited; it is performed to exclude postseptal involvement in case of clinical suspicion or non-response.
Criteria
Infection has spread to orbital fat posterior to the orbital septum but organized abscess formation has not yet developed. Proptosis, chemosis, and restriction of eye movements are clinically present. CT shows diffuse infiltration of orbital fat and obliteration of fat planes.
Distinct Features
No organized collection or abscess cavity is present. Intravenous broad-spectrum antibiotic therapy is the primary approach. If no response to treatment, CT follow-up is needed for abscess formation. Most cases achieve complete resolution with conservative treatment.
Criteria
Organized purulent fluid collection has formed beneath the periosteum. It is localized along the medial orbital wall (from ethmoid sinusitis) or superior orbital wall (from frontal sinusitis). CT shows a peripherally enhancing crescent-shaped hypodense collection. Globe may be displaced laterally or inferiorly.
Distinct Features
Surgical drainage is indicated in the following situations: non-response to medical treatment within 24-48 hours, patients over 10 years of age, large abscess (>10 mm), decreased visual acuity, laterally or inferiorly located abscess. In children under 10 years with small (<10 mm) medial abscesses, conservative approach with intravenous antibiotics may be attempted.
Criteria
Organized abscess cavity has formed within the orbital fat tissue. May develop from rupture of subperiosteal abscess into orbital fat or from direct hematogenous spread. Marked proptosis, ophthalmoplegia, and vision loss accompany. CT shows a peripherally enhancing irregularly bordered collection within the orbital fat.
Distinct Features
Urgent surgical drainage is indicated. Requires emergency intervention due to risk of optic nerve compression and central retinal artery occlusion. High risk of progression to cavernous sinus thrombosis. Postoperative CT control is necessary to evaluate drainage adequacy.
Criteria
Spread of orbital infection to the cavernous sinus through valveless ophthalmic veins. Bilateral cranial nerve involvement (III, IV, V1, V2, VI), bilateral proptosis and chemosis may develop. Contrast-enhanced MRI/MR venography shows expansion, irregular enhancement, and filling defect (thrombosis) of the cavernous sinus.
Distinct Features
Life-threatening emergency. Requires intensive care, intravenous broad-spectrum antibiotics, and anticoagulation. Mortality rate can reach up to 30%. Risk of contralateral orbit involvement, meningitis, and cerebral abscess. MR venography is the gold standard for diagnosis of cavernous sinus thrombosis.
Distinguishing Feature
Idiopathic orbital inflammation (pseudotumor) typically develops without sinusitis, shows orbital fat infiltration and extraocular muscle thickening on CT/MRI but no subperiosteal abscess or sinus opacification. Dramatic response to steroid treatment supports the diagnosis. Fever and leukocytosis are more prominent in cellulitis.
Distinguishing Feature
IgG4-related orbital involvement follows a chronic course, bilateral lacrimal gland enlargement is common, and serum IgG4 levels are elevated. MRI shows T2 hypointense mass (fibrosis) and homogeneous enhancement. Acute infection findings (fever, pain, leukocytosis, sinusitis) are absent.
Distinguishing Feature
Bilateral symmetric extraocular muscle thickening (muscle belly involvement with tendon sparing) is characteristic of thyroid ophthalmopathy. Fever, pain, and sinusitis findings are absent. Inferior and medial rectus are the most commonly affected muscles. Thyroid function tests are abnormal. Orbital fat volume increase is seen but infectious infiltration pattern is absent.
Distinguishing Feature
Orbital lymphoma typically presents with painless proptosis and subacute/chronic course. MRI shows a homogeneous, low-to-intermediate signal mass on T1 and T2, demonstrating a moulding pattern to surrounding structures. Sinusitis findings are absent. Diffusion restriction is prominent but no abscess cavity or ring enhancement is present.
Distinguishing Feature
Rhabdomyosarcoma appears as a rapidly growing, well-defined or aggressively marginated homogeneously enhancing mass in children. It may show bone destruction (erosion is more limited in cellulitis) and intracranial extension. Sinusitis is not associated. Solid mass component and necrosis areas differ from abscess cavity. Clinically, fever and infection findings are usually absent.
Urgency
emergentManagement
medicalBiopsy
Not NeededFollow-up
24-48 saat içinde klinik yanıt değerlendirmesi; yanıtsızlıkta kontrol BT. Subperiosteal apse: cerrahi drenaj endikasyonu değerlendirmesi. Kavernöz sinüs tutulumu şüphesinde acil MR venografi.Orbital cellulitis is an emergency and delayed treatment can lead to life-threatening complications including permanent vision loss, cavernous sinus thrombosis, meningitis, and cerebral abscess. While preseptal cellulitis can usually be treated with oral antibiotics, postseptal cellulitis requires intravenous broad-spectrum antibiotics. In subperiosteal abscess, surgical drainage indication should be evaluated (based on age, abscess size, visual status, and treatment response). Chandler classification is used for staging and treatment planning: Stage I (preseptal), Stage II (postseptal orbital cellulitis), Stage III (subperiosteal abscess), Stage IV (orbital abscess), Stage V (cavernous sinus thrombosis).
Requires urgent IV antibiotic therapy. Surgical drainage is indicated for subperiosteal abscess formation. Risk of progression to cavernous sinus thrombosis (life-threatening complication). Vision loss may develop.