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Neuroradiology Case of the Week
Case 342
August 2008
Harshabad Singh,MBBS, Rajiv Mangla, MD,
and
P-L Westesson, MD, PhD, DDS
Clinical
Presentation: Patient is a 4-year-old child with a history of eye proptosis and inability to fully abduct right eye. Progressive swelling with eye pain.
Imaging Findings: Computed tomography is essential for staging orbital cellulitis. It allows a clear differentiation of the inflammatory process that is occurring in the orbit and shows how the orbital contents are being affected by infection.
Axial views better demonstrate the displacement of the medial rectus muscle and the abscess within the orbit, whereas coronals cuts are useful to delineate orbital and sinus anatomy.
A medial subperiosteal abscess is seen on CT scans as a rim-enhancing mass within the orbit, next to the lamina papyracea displacing the medial rectus laterally. Edema and thickening of the medial rectus are also evident, when compared with the opposite side.
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Figure 1: Contrast-enhanced axial CT image shows a well-marginated collection along the medial wall of right orbit. The collection shows marginal enhancement and displaces the medial rectus. There is evidence of proptosis. The right-sided ethmoidal air cells show evidence of sinusitis. |
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| Figure 2: Coronal reformatted image shows lateral and inferior displacement of the right globe by the subperiosteal abscess on the medial orbital wall. There is evidence of right ethmoidal sinusitis. |
Diagnosis: Subperiosteal abscess
Discussion: Orbital infections develop via direct inoculation, extension from adjacent structures, and hematogenous spread. Sinusitis and upper respiratory tract infection are the two most common predisposing factors. The ease and rapidity of such infectious spread relates to the facial venous system, which has a great number of anastomoses and is entirely valveless.
Other causes include dental abscesses, trauma, closed fractures, periocular surgery, panopthalmitis, septicemia and immunosuppression [1].
The common causative organisms include Staphylococcus aureus, Streptococcus sps and Bacteroides. Some patients also have polymicrobial infection. Fungal infections although less common than bacterial occur more commonly in immunocompromised patients.
Orbital infections may be subdivided into five groups (Chandler, et al.) [2].
- Group I - Preseptal cellulitis
- Group II - Orbital cellulitis
- Group III - Subperiosteal abscess
- Group IV - Orbital abscess
- Group V - Cavernous sinus thrombosis
The subperiosteal abscess is formed due collection of pus between the orbital periosteum and orbital bone.This pushes the globe,usually downward and outward,thus causing directional proptosis(a.c.f. frontally directed proptosis in an orbital abscess).The patient also has limited ocular movement and signs of postseptal spread of infection like proptosis and chemosis. Un ess treated urgently and optimally spread of infection can cause extra and intra-cranial complications. Opthalmic vein thrombosis, traction on optic nerve or optic neuritis can cause vision loss. Intracranial spread may cause subdural empyema, intracranial abscesses,meningitis or cavernous sinus thrombosis [3 & 4].
Contrast enhanced CT is the diagnostic modality of choice and shows the subperiosteal abscess as a sharply defined, extraconal. space occupying mass with marginal ring enhancement. The corresponding rectus may be displaced by the abscess. On T1W MR Images it shows an intermediate signal with rim enhancement after contrast administration. The subperiosteal abscess is hyperintense on T2W MR Images [5]. MRI is the diagnostic modality of choice for evaluating intracranial complications. MRI is superior to CT in identifying marrow space abnormalities such as edema or osteomyelitis, inflammation of the meninges, extra-axial empyemas, and early cerebritis. It also provides superior soft tissue detail and does not expose the patient to radiation. However, an MRI study takes a lot longer than CT scanning, is sensitive to motion artifact, requires general anesthesia in younger children and sedation in older children. Thus an MRI should be done in case of clinical evidence or equivocal CT findings suggesting intracranial spread. Orbital ultrasound can be used as a bedside noninvasive test to monitor the progress of the infection. However it lacks sensitivity in identifying lesions in the posterior orbit [6].
Initial management of subperiosteal abscess includes parentral broad spectrum antibiotics. Indications for surgical drainage are deterioration in visual acuity, progression of orbital signs and symptoms and no improvement after 48 hours of medical treatment. Surgical approaches to drain medial orbital abscesses can be divided into open, transnasal endoscopic, or combined approaches.The endoscopic approach is preferred as it provides magnified visualization of the surgical field, allows comprehensive treatment of the orbital abscess and the offending paranasal sinuses and also obviates the need for facial incisions [7].
References:
- Pereira FJ, Velasco e Cruz AA, Anselmo-Lima WT, Elias Júnior J. Computed tomographic patterns of orbital cellulitis due to sinusitis. Arq Bras Oftalmol. 2006 Jul-Aug;69(4):513-8.
[PubMed]
- Chandler JR, Langenbrunner DJ, Stevens ER. The pathogenesis of orbital complications in acute sinusitis. Laryngoscope. 1970;80(9):1414-28. [PubMed]
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Maroldi R, Nicolai P. Imaging in Treatment Planning for Sinonasal Diseases. Springer-Verlag, 2005: 59-61.
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Som PM, Curtin HD. Head and Neck Imaging, 4th ed. Mosby, 2003: 580-581
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Müller-Forell WS (ed). Imaging of Orbital and Visual Pathway Pathology. Springer-Verlag, 2002: 253-254.
- Fakhri S, Pereira K. Endoscopic management of orbital abscesses. Otolaryngol Clin North Am. 2006 Oct;39(5):1037-47, viii. [PubMed]
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