Other / Other / MRI

Chorioretinitis

Chorioretinitis is inflammation of the retina and choroid, often presenting as a manifestation of congenital infections (rubella, CMV, toxoplasmosis), or systemic diseases (tuberculosis, syphilis). Cross-sectional imaging (CT/MRI) is performed when chronic changes are suspected or to evaluate for complications and differentiate inflammatory processes from masquerade syndromes.

Key Images

CMV

CMV

CMV

Look For First
  • Gadolinium enhancement of the uveal tract (enhancing layer immediately deep to the low-signal sclera)
  • Abnormal retinal thickening (>1.2 mm) and hyperintensity on gadolinium-enhanced turbo FLAIR sequences
  • Posterior calcifications on CT, particularly in chronic stages
Key Image Findings
  • Gadolinium-enhanced MRI shows characteristic increased enhancement of the uveal tract, visualized as an enhancing layer immediately deep to the low-signal sclera, which is the most common finding regardless of etiology.
  • Abnormal retinal thickening greater than 1.2 mm with hyperintensity is most conspicuous on gadolinium-enhanced turbo FLAIR sequences, allowing for precise visualization of retinal involvement.
  • Diffusion-weighted imaging (DWI) may reveal diffusion restriction within the uvea and subretinal effusions in cases of posterior uveitis, aiding in identification of active inflammation.
  • Inflammatory nodules adherent to the uvea are visible on contrast-enhanced MRI and may represent sites of infectious or inflammatory activity.
  • Vitreous humor abnormalities (haze, vitritis) and perineural/perimuscular enhancement may accompany uveal inflammation on MRI.
  • CT findings in chronic stages include uveoscleral thickening, contrast enhancement, and development of posterior globe calcifications.
  • MRI is superior for differentiating inflammatory chorioretinitis from masquerade syndromes such as lymphoma based on enhancement patterns and lesion morphology.
  • Assessment of potential intracranial extension and orbital involvement within systemic inflammatory conditions is best performed with neuroimaging and orbital MRI protocols.
Differential Diagnosis
  • Lymphoma and other masquerade syndromes: differentiated by enhancement patterns and morphology on gadolinium-enhanced MRI, with lymphoma typically showing different enhancement characteristics.
  • Posterior scleritis: presents with uveoscleral thickening and enhancement but lacks the characteristic retinal hyperintensity and uveal tract enhancement pattern.
  • Infectious retinitis (CMV, HSV): may show similar retinal involvement but distribution and associated findings differ based on specific viral etiology.
  • Acute retinal necrosis: characterized by more extensive outer retinal involvement and rapid progression compared to indolent chorioretinitis.
  • Retinal detachment (rhegmatogenous or tractional): distinguished by imaging morphology; does not show uveal enhancement or retinal hyperintensity on FLAIR.
  • Ocular/orbital granulomas from sarcoidosis or tuberculosis: differentiated by systemic imaging findings and clinical context rather than purely on ophthalmologic imaging characteristics.
Discussion

Chorioretinitis represents a spectrum of posterior uveitis with diverse etiologies including congenital infections (rubella, CMV, toxoplasmosis), tuberculosis, and syphilis, each requiring different treatment regimens.

Toxoplasma chorioretinitis is treated with oral trimethoprim-sulfamethoxazole or pyrimethamine-sulfadiazine, while CMV retinitis requires systemic ganciclovir or valganciclovir, making accurate etiology crucial.

Macular involvement is associated with worse visual prognosis, necessitating careful assessment of lesion location on imaging to guide clinical counseling and treatment urgency.

MRI with gadolinium enhancement is the optimal cross-sectional imaging modality for evaluating posterior uveitis and chorioretinitis, offering superior soft tissue contrast for detecting uveal, retinal, and associated inflammatory changes.

DWI sequences can identify active inflammatory processes by detecting diffusion restriction within the uvea and subretinal effusions, aiding in assessment of disease activity.

Chronic chorioretinitis may progress to globe calcification, making CT imaging valuable for detecting late-stage sequelae and assessing for phthisical changes.

Cross-sectional radiology (CT/MRI) is rarely employed for chorioretinitis, which is fundamentally a clinical and ophthalmic-imaging diagnosis — no displayable CT or MRI figures for chorioretinitis were retrieved in the literature, though the radiologic findings are well described.

[1] On the standard cross-sectional modalities, chorioretinitis/posterior uveitis manifests as:

MRI — increased gadolinium enhancement of the uveal tract (seen as the enhancing layer immediately deep to the low-signal sclera), with choroidal thickening and/or hyperenhancement from increased capillary permeability; abnormal vitreous signal on FLAIR from altered protein content; and, in cases with subretinal effusion, restricted diffusion on DWI within the uvea and effusions.

[1]

CT — uveoscleral thickening and enhancement, sometimes with posterior calcification in chronic disease; in parasitic (Toxocara) chorioretinitis, a noncalcified focal intraocular mass with irregular thickening of the uveoscleral coat and a normal-size globe (calcification favors retinoblastoma instead

Reporting Pearls

When reporting chorioretinitis on MRI, clearly describe the uveal tract enhancement pattern (enhancing layer deep to the sclera), quantify retinal thickening in millimeters, note the presence of subretinal effusions on DWI, specify macular involvement status, and comment on any perineural or perimuscular inflammation to guide clinical prognosis and treatment decisions.

Pitfalls
  • Confusing posterior scleritis with chorioretinitis based on uveoscleral thickening alone; look for the characteristic uveal tract hyperenhancement and retinal hyperintensity on FLAIR sequences specific to chorioretinitis.
  • Underestimating the importance of macular involvement; carefully assess whether central macula is affected, as this has significant prognostic implications for visual outcome.
  • Failing to perform or interpret DWI sequences, which can reveal active inflammation and subretinal effusions that may not be apparent on conventional T2/FLAIR imaging alone.
  • Over-relying on CT imaging when MRI with gadolinium enhancement is superior for detecting acute inflammatory changes and differentiating chorioretinitis from masquerade syndromes; CT is primarily useful for detecting chronic calcifications.
Source: Reference source