Spectrum of Orbital Cellulitis on Magnetic Resonance Imaging

Qualitative and Quantitative Magnetic Resonance Imaging in Bacterial Orbital Cellulitis

PURPOSE

To summarise the qualitative and quantitative parameters of bacterial orbital cellulitis (OC) on magnetic resonance imaging (MRI) and explore their clinical correlations.

METHODS

Multi-centre retrospective study with inclusion of patients of all ages with OC who underwent MRI. Patients with isolated pre-septal cellulitis, bilateral disease and poor-quality scans were excluded. An enlargement ratio for extraocular muscles (EOMs) was calculated by dividing maximal EOM measurements from the affected side by the contralateral side.

RESULTS

Twenty MRI scans from twenty patients (Mean age: 40.8 ± 24.3 years old, M: F = 15:5) between 2011 and 2022 were analysed. Three (15.0%) cases were paediatric patients (<18 years old). All cases had both pre-septal and orbital fat involvement. The EOM were affected in nineteen cases, with the superior muscle complex (18/19, 94.7%) most commonly affected. Mean enlargement ratio (1.30, Range: 1.04-1.82) was greatest for the medial rectus on axial views on T1 and fat-suppressed contrast-enhanced T1 (FS CE T1). Optic peri-neuritis was present in eleven (55.0%) patients, whilst two (9.5%) cases had optic neuritis. A greater degree of proptosis was observed in patients with optic neuropathy and those who underwent surgical intervention compared to those without (p = .002 and p = .002, respectively).

CONCLUSION

MRI remains an important imaging modality for evaluating complicated OC. However, qualitative features may lack accuracy and is not a reproducible means of analysis. Simple quantitative parameters, such as proptosis and EOM measurements, correlate with high-risk clinical features and may have utility in predicting clinical course.

Orbital Fat Density as a Diagnostic Tool in Pre-Septal and Orbital Cellulitis

PURPOSE

To evaluate the usefulness of measuring orbital fat density in identifying post-septal involvement when initial differential diagnosis between orbital and periorbital cellulitis (OC and POC) is unclear.

MATERIALS AND METHODS

Retrospective study of patients with clinical diagnosis of OC or POC who underwent contrast-enhanced computerized tomographic scans over a span of 10 years. Intraconal orbital fat density was measured with Hounsfield units (HU) in six areas on axial scans consisting of nasal and temporal intraconal sites. These measurements correlated with the initial and final diagnoses. Main outcome measures were HU values at the initial and final diagnoses.

RESULTS

Fifty-seven patients were included. Mean HU measurement was -52 ± 18 HU for the involved side vs. -63 ± 13 for the uninvolved side (P < .001). The values were higher in cases of a final diagnosis of OC in the involved side (P < .001). The HU values were significantly higher in the nasal vs. the temporal locations of each orbit bilaterally (P < .001). The initial POC diagnosis of 20 patients (35%) was revised to OC.

CONCLUSION

Intraconal fat density measurements can assist in the primary assessment of orbital involvement in patients with an uncertain initial diagnosis, with a HU value higher than -50 is suggestive of orbital involvement.

High risk and low prevalence diseases: Orbital cellulitis

INTRODUCTION

Orbital cellulitis is an uncommon but serious condition that carries with it a potential for significant morbidity.

OBJECTIVE

This review highlights the pearls and pitfalls of orbital cellulitis, including presentation, diagnosis, and management in the emergency department (ED) based on current evidence.

DISCUSSION

Orbital cellulitis refers to infection of the globe and surrounding soft tissues posterior to the orbital septum. Orbital cellulitis is typically caused by local spread from sinusitis but can also be caused by local trauma or dental infection. It is more common in pediatric patients compared to adults. Emergency clinicians should first assess for and manage other critical, sight-threatening complications such as orbital compartment syndrome (OCS). Following this assessment, a focused eye examination is necessary. Though orbital cellulitis is primarily a clinical diagnosis, computed tomography (CT) of the brain and orbits with and without contrast is critical for evaluation of complications such as abscess or intracranial extension. Magnetic resonance imaging (MRI) of the brain and orbits with and without contrast should be performed in cases of suspected orbital cellulitis in which CT is non-diagnostic. While point-of-care ultrasound (POCUS) may be useful in differentiating preseptal from orbital cellulitis, it cannot exclude intracranial extension of infection. Management includes early administration of broad-spectrum antibiotics and ophthalmology consultation. The use of steroids is controversial. In cases of intracranial extension of infection (e.g., cavernous sinus thrombosis, abscess, or meningitis), neurosurgery should be consulted.

CONCLUSION

An understanding of orbital cellulitis can assist emergency clinicians in diagnosing and managing this sight-threatening infectious process.

Focus on Ophthalmopathology - Orbital Infections from Hordeolum to Necrotizing Fasciitis

(Peri)orbital infections comprise a multitude of diagnoses, ranging from common hordeolum to rare but life-threatening necrotizing fasciitis. However, these disease entities are rarely diagnosed by an ophthalmic pathologist because (peri)orbital infections are usually diagnosed clinically, with the help of imaging and microbiological techniques when indicated. In this review article, the role of ophthalmopathology in the diagnosis of (peri)orbital infections is illustrated on the basis of several exemple diagnoses. An infectious hordeolum must be distinguished from a noninfectious chalazion. A nodular thickening of the eyelid, which is diagnosed and treated as a chalazion, can hide a malignant neoplasia. The correct diagnosis and treatment of canaliculitis is often delayed. In this context the most common causative organism, Actinomyces, can be depicted histologically, as can lacrimal stones/dacryoliths. Necrotizing fasciitis is a rapidly worsening infection of the fascia, which can lead to necrosis, sepsis, and death. During the Sars-CoV2 pandemic, an increased incidence of mucormycosis cases was observed, especially in India. This superinfection was facilitated by the widespread use of steroids and immunosuppression. Histologically, it is possible to visualize infiltration of vessel walls by the fungus. Ophthalmopathology contributes to the diagnosis and to understanding the pathophysiology of these diseases.

Extraocular muscle enlargement

Extraocular muscle enlargement can occur secondary to a range of orbital and systemic diseases. Although the most common cause of extraocular muscle enlargement is thyroid eye disease, a range of other inflammatory, infective, neoplastic, and vascular conditions can alter the size and shape of the extraocular muscles. Imaging with computed tomography and magnetic resonance imaging plays an essential role in the workup of these conditions. This article provides an image-rich review of the wide range of pathology that can cause enlargement of the extraocular muscles.