KEY FACTS Terminology C hronic l ymphocytic i nflammation with p ontine p erivascular e nhancement r esponsive to s teroids (CLIPPERS) Predominantly involving brainstem, adjacent rhombencephalic structures Shows clinical, imaging response to glucocorticosteroids Imaging Location: Predominately pons May extend into cerebellar peduncles, hemispheres Caudally into medulla, spinal cord Rostrally into midbrain MR Classic: Enhancing punctate/curvilinear lesions; pons often appears “peppered”; may exhibit subtle radiating pattern…

KEY FACTS Terminology Autoimmune-mediated white matter (WM) demyelination of brain &/or spinal cord, usually with remyelination Imaging Best diagnostic clue: Multifocal WM and deep gray lesions days to weeks following infection/vaccination May involve both brain and spinal cord; WM > gray matter, but usually both affected Deep/juxtacortical WM > periventricular WM Both supratentorial and infratentorial lesions Multifocal punctate to large flocculent FLAIR hyperintensities Do not usually…

KEY FACTS Terminology Synonyms: Devic disease, optic-spinal multiple sclerosis Definition: Autoimmune inflammatory disorder involving myelin of neurons of optic nerves and spinal cord, with limited brain parenchymal involvement Imaging Longitudinally extensive (> 3 vertebral segments) T2 hyperintensity within cord + enhancement of optic nerves (85% of cases) T2 abnormality tends to involve entire cross section of cord, unlike more focal involvement of MS Top Differential Diagnoses…

KEY FACTS Imaging Multiple perpendicular callososeptal T2 hyperintensities characteristic of multiple sclerosis (MS) Perivenular extension: “Dawson fingers” Bilateral, asymmetric linear/ovoid FLAIR hyperintensities > 85% periventricular/perivenular 50-90% callososeptal interface May also commonly involve subcortical U fibers, brachium pontis, brainstem, spinal cord common Transient enhancement during active demyelination > 90% disappear within 6 months Rare: Large tumefactive enhancing rings T1: Hypointense lesions suggest worse prognosis Correlate with disability,…

KEY FACTS Terminology HIV/AIDS-related opportunistic infections and neoplasms Imaging Findings Primary CNS lymphoma: Enhancing lesions, often hemorrhagic/necrotic within basal ganglia, periventricular white matter Kaposi sarcoma: Intense enhancing soft tissue mass in scalp Bacterial abscesses: Ring-enhancing lesion with ↑ signal on DWI Aspergillosis: Multiple ring-enhancing lesions Neurosyphilis: Cortical/subcortical infarcts, granulomas, leptomeningeal enhancement Benign lymphoepithelial lesions of HIV: Multiple cystic masses enlarging both parotid glands MR is most…

KEY FACTS Terminology I mmune R econstitution I nflammatory S yndrome (IRIS) Atypical/worsening opportunistic infection HIV/AIDS patients following commencement of HAART Patients with MS, immunomodulatory therapy Imaging Progressive multifocal leukoencephalopathy (PML)-IRIS White matter (WM) hypodensities with ↑ mass Patchy atypical enhancement TB-IRIS ↑ leptomeningeal enhancement ↑ size of ring-/nodular-enhancing tuberculomas Crypto-IRIS ↑ nodular meningeal/subependymal enhancement ↑ in size of “gelatinous” pseudocysts Top Differential Diagnoses Diffuse/patchy WM…

KEY FACTS Terminology Progressive multifocal leukoencephalopathy (PML) Subacute opportunistic infection caused by DNA virus JC polyomavirus (JCV) JCV infects oligodendrocytes, causes demyelination in immunocompromised patients Associated with immunosuppression, often AIDS Organ transplant, cancer, chemotherapy, myeloproliferative disease, and steroid treatment Reported in treatment for multiple sclerosis and in rheumatic diseases Imaging Multifocal T2-hyperintense demyelinating plaques involve subcortical white matter (WM), extend to deep WM; gray matter often…

KEY FACTS Terminology Cryptococcus neoformans infection Opportunistic fungal infection that typically affects HIV and other immunosuppressed patients Cryptococci spread along perivascular spaces (PVS) to deep brain: Basal ganglia, thalamus, brainstem, cerebellum, dentate nucleus, periventricular WM Imaging Dilated PVS in deep gray nuclei of AIDS patient, often no enhancement Degree of enhancement depends on cell-mediated immunity of host May see miliary or leptomeningeal enhancing nodules + gelatinous…

KEY FACTS Terminology Coccidioidomycosis, histoplasmosis (sporadic, common) Blastomycosis (rare, sporadic, generally lungs/skin) Invasive fungal infection (immunocompromised) Candidiasis (common) Aspergillus, mucormycosis (angioinvasive) Imaging Varies with type, site of infection, immune status MR ± contrast (add T2* for hemorrhage) Invasive fungal sinusitis Most common in immunocompromised patient Aspergillus, mucormycosis most common Bone CT shows sinus/orbit/skull base involvement Look for occluded carotid, thrombosed cavernous sinus Meningitis Most common presentation…

KEY FACTS Terminology Acquired CNS cytomegalovirus (CMV) infections: Meningitis, encephalitis, ventriculitis, transverse myelitis, radiculomyelitis, chorioretinitis Immunocompromised (AIDS, organ transplant) patients are at risk → reactivation of previously silent infection Imaging Best diagnostic clue: Ventriculitis with fluid-debris level and ependymal enhancement in immunocompromised patient Encephalitis: Ill-defined T2-hyperintense area, variable enhancement May mimic HIV encephalitis with patchy nonspecific T2-hyperintense lesions Contrast should be used for imaging of all…

KEY FACTS Terminology Opportunistic infection Caused by parasite Toxoplasma gondii Most common opportunistic CNS infection in AIDS Imaging CT Ill-defined, hypodense lesions and edema Basal ganglia, thalamus, cerebellum Rim, nodular, target enhancement MR T2 hypointense T1 C+ target sign highly suggestive Thallium-201 SPECT and 18F-FDG PET: Toxoplasmosis lesions are hypometabolic Top Differential Diagnoses Lymphoma Solitary mass in patient with HIV/AIDS? Lymphoma > toxoplasmosis Lymphoma often restricts…

KEY FACTS Terminology HIV-1 encephalitis/HIV-1 encephalopathy HIV-associated neurocognitive disorders Imaging CT Atrophy Bilateral periventricular/diffuse WM hypointensities Basal ganglia, cerebellum, brainstem hypodensity MR Diffuse “hazy” hyperintense WM on T2/FLAIR Nonenhancing (if enhancement present, consider opportunistic infections, immune reconstitution inflammatory syndrome) Pathology HIV has ability to cause neurologic disease Does not replicate within neural/glial cells Microglial nodules with multinucleated giant cells WM pallor early, neocortical infection/atrophy late Clinical…

KEY FACTS Terminology Lyme disease, Lyme neuroborreliosis (LNB) Multisystem inflammatory disease Caused by spirochete Borrelia burgdorferi (USA) Transmitted by Ixodes tick bite Reservoirs = white tail deer/field mouse Imaging MS-like white matter (WM) lesions (may enhance) 2-8 mm (large “tumefactive” lesions rare) ± multiple enhancing cranial nerves ± cauda equina, meningeal enhancement Top Differential Diagnoses Demyelinating disease Vasculitis Sarcoidosis Bell's palsy (solitary CN 7 enhancement) Chronic…

KEY FACTS Terminology Intracranial parasitic infection caused by pork tapeworm Taenia solium 4 pathologic stages: Vesicular, colloidal vesicular, granular nodular, and nodular calcified Imaging Best diagnostic clue: Cyst with “dot” inside Convexity subarachnoid spaces most common location Inflammatory response around cyst may seal sulcus, making lesions appear intraaxial May involve cisterns > parenchyma > ventricles Intraventricular cysts are often isolated Basal cistern cysts may be racemose…

KEY FACTS Terminology Typically causes tuberculous meningitis &/or localized CNS infection, tuberculoma Imaging Basilar meningitis + extracerebral TB (pulmonary) Meningitis + parenchymal lesions highly suggestive Tuberculomas Supratentorial parenchyma most common Usually T2 hypointense Enhances strongly (solid or ring enhancing) Tuberculous abscess: Multiloculated ring enhancement MR with FLAIR, DWI, T1 C+, ± MRA, MRS TB abscess has prominent lipid, lactate but no amino acid resonances Top Differential…

KEY FACTS Terminology Acute cerebellitis Imaging Bilateral cerebellar hemispheric gray and white matter low attenuation (NECT), T2/FLAIR hyperintensity (MR); unilateral involvement less common Confluent regions of T2 prolongation, affecting gray and white matter ± pial or subtle parenchymal enhancement DWI/ADC → affected regions typically show increased diffusivity Top Differential Diagnoses Acute disseminated encephalomyelitis (ADEM) Infiltrating cerebellar neoplasm Cerebellar infarct Pathology Reported in association with varicella, Epstein-Barr,…

KEY FACTS Terminology Diffuse brain parenchymal inflammation caused by variety of pathogens, most commonly viruses Location dependent on etiology Imaging Abnormal T2 hyperintensity of gray matter ± white matter or deep gray nuclei Large, poorly delineated areas of involvement common, ± patchy hemorrhage Imaging is often nonspecific, mimics other etiologies Top Differential Diagnoses Acute ischemia Autoimmune encephalitis Herpes encephalitis Status epilepticus Toxic/metabolic lesions Pathology Most (but…

KEY FACTS Terminology West Nile virus (WNV), West Nile fever, West Nile neuroinvasive disease Mosquito-transmitted acute meningoencephalitis Imaging Head CT usually normal MR with DWI, T1 C+ Classic: Bilateral basal ganglia, thalamic hyperintensity Patchy, poorly demarcated hyperintense foci in cerebral white matter on T2WI/FLAIR Enhancement usually absent (has been reported) DWI may show restricted diffusion Other sites of involvement Brainstem Corpus callosum splenium Mesial temporal lobes…

KEY FACTS Terminology Encephalitis caused by human herpes virus 6 (HHV-6) Imaging Immunocompromised patient with abnormal signal medial temporal lobe(s) Limbic system: Hippocampus, amygdala, parahippocampal gyrus Insular region, inferior frontal lobe involvement less common than herpes simplex encephalitis Atypical pattern in infants/children (basal ganglia, thalami, cerebellum, brainstem) Best imaging: MR (coronal T2/FLAIR, DWI, T1 C+) Top Differential Diagnoses Herpes simplex virus (HSV) encephalitis Early HHV-6 exclusive…

KEY FACTS Terminology Brain parenchyma infection caused by herpes simplex virus type 1 (HSV1) Typically reactivation in immunocompetent patients Imaging Best imaging clue: T2/FLAIR hyperintensity of limbic system (medial temporal and inferior frontal cortex) with DWI restriction Typically bilateral disease, but asymmetric Deep gray nuclei usually spared CT often normal early MR with DWI most sensitive for early diagnosis T2/FLAIR: Cortical, subcortical hyperintensity with relative white…