Ring-Enhancing Lesions
Bernadette L. Koch, MD
DIFFERENTIAL DIAGNOSIS
Common
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Abscess
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Pilocytic Astrocytoma
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Neurocysticercosis
Less Common
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Demyelinating Disease
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ADEM
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Multiple Sclerosis
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Ganglioglioma
Rare but Important
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Aneurysm (Thrombosed)
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Other Infections
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Tuberculosis
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Fungal Diseases
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Acquired Toxoplasmosis
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Lyme Disease
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Other Neoplasms
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Parenchymal Metastases
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Lymphoma, Primary CNS
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Glioblastoma Multiforme
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Subacute Cerebral Infarction
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Subacute Intracerebral Hematoma
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
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Solitary ring-enhancing lesions most often tumor, infection, or demyelination
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Metastatic lesions typically subcortical; primary tumors more often deep
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Smooth, thin rim of enhancement typical of organizing abscess
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Thick, irregular rim of enhancement suggests necrotic neoplasm
Helpful Clues for Common Diagnoses
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Abscess
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Pyogenic, fungal, granulomatous, or parasitic
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Single or multiple
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Thin, smooth rim contrast enhancement (CE)
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Thin T2 hypointense rim
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Restricted diffusion central cavity
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MRS: ↑ amino acids (0.9 ppm), succinate (2.4 ppm), and acetate (1.92 ppm)
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Early capsule stage: Moderate vasogenic edema and mass effect
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Late capsule stage: Edema & mass effect ↓
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± ventriculitis &/or meningitis
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± sinusitis or mastoiditis as a cause
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Pilocytic Astrocytoma
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Cerebellum > optic nerve/chiasm > adjacent to 3rd ventricle > brainstem
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Peak: 5-15 years of age
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Variable appearance
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Nonenhancing cyst + CE mural nodule
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CE cyst wall + CE mural nodule
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Solid with necrotic center + heterogeneous CE
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Solid + homogeneous CE
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Cyst may accumulate contrast on delayed imaging
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“Aggressive” metabolite spectrum on MRS: ↑ choline, ↓ NAA; however, clinical behavior frequently benign
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Neurocysticercosis
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Pork tapeworm, Taenia solium
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5-20 mm cyst
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± 1-4 mm eccentric scolex
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Single or multiple
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Cisterns > parenchyma > intraventricular
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Appearance depends on developmental stage and host response
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Simple cyst ± enhancement → complicated cyst + thick enhancing wall
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± surrounding edema
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± calcification in healed stage
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Helpful Clues for Less Common Diagnoses
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Demyelinating Disease
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ADEM
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Autoimmune-mediated demyelination: Brain and spinal cord
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Typically monophasic, 10-14 days after viral infection or vaccination
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“Multiphasic” or “relapsing” ADEM may be same entity as MS
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Multifocal hyperintense T2 and FLAIR signal WM and BG > GM; cerebrum > cerebellum and brainstem
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Bilateral common, but asymmetric
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Punctate or ring-like enhancement (complete or incomplete)
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MRS: ↓ NAA, ± ↑ lactate and choline in acute lesions
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Multiple Sclerosis
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Probably autoimmune-mediated demyelination in genetically susceptible individuals
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Relapsing-remitting course
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Imaging may be identical to ADEM
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Multifocal lesions PVWM, subcortical U-fibers, brachium pontis, brainstem, and spinal cord
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Infratentorial: Children > adults
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Perivenular extension along path of deep medullary veins = “Dawson fingers”
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T1WI: Hypointense lesions = axonal destruction (“black holes”)
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T2 and FLAIR: Hyperintense linear foci radiating from ventricles
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Nodular or ring enhancement, occasionally semilunar CE or large tumefactive enhancing rings
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MRS: ↓ NAA, ↑ choline, ↑ myoinositol
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Ganglioglioma
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Temporal > parietal > frontal > occipital > BG/thalamus, hypothalamus/optic pathway, cerebellum
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Solid, cystic, or mixed; usually cortical-based lesion, without surrounding edema
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Ca++ common
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Larger and more cystic lesions in children
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Variable degree of CE: Diffuse or ring-like
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Marked meningeal enhancement in desmoplastic infantile ganglioglioma
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Rarely poorly defined, infiltrating lesion
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Helpful Clues for Rare Diagnoses
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Aneurysm (Thrombosed)
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Partially or completely thrombosed
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Laminated appearance of thrombus
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± pulsation artifact on MR
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Other Infections
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Tuberculosis: Mycobacterium tuberculosis infection
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CNS TB usually with pulmonary TB
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Thick basilar meningitis
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± dural-based tuberculomas
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± parenchymal tuberculomas
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Multiple > solitary tuberculomas
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Solid CE or necrotic center
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Fungal Diseases: Rare, usually in immunocompromised patients
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Nocardia, blastomycosis, candidiasis, coccidiomycosis, histoplasmosis
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Multiple > single
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Acquired Toxoplasmosis: Single or multiple; nodular or ring CE; immunocompromised patients, esp. HIV+
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Lyme Disease: Multifocal PVWM lesions ± CE; cranial nerve CE common; rash and flu-like symptoms
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