SUMMARY:Since its initial description, there have been significant changes in the epidemiology, pathogenesis, and clinical and imaging manifestations of JCV infection of brain. The most common clinical manifestation is PML. Other recently described CNS manifestations are JCE, JCVGCN, and JCM. Although AIDS is the most common predisposing factor for JCV reactivation, there is increasing incidence of brain manifestations of JCV reactivation in non-HIV settings, including different rheumatologic, hematologic, and oncologic conditions; monoclonal antibody therapy; transplant recipients; primary immunodeficiency syndromes; and even in patients without any recognizable immune deficiency. IRIS may develop secondary to restoration of immunity in HIV-positive patients with PML receiving antiretroviral therapy. This is of profound clinical significance and needs to be diagnosed promptly. Imaging plays a crucial role in the diagnosis of the disease, monitoring of treatment response, identifying disease progression, and predicting prognosis. In this article, current understanding of the epidemiology, pathogenesis, clinical presentations, and all aspects of imaging of JCV infection of the brain have been comprehensively reviewed.ABBREVIATIONS: ADC ϭ apparent diffusion coefficient; CNS ϭ central nervous system; cPML ϭ classic PML; Cr ϭ creatine; CTL ϭ cytotoxic T-lymphocytes; DWI ϭ diffusion-weighted imaging; FLAIR ϭ fluid-attenuated inversion recovery; HAART ϭ highly active antiretroviral therapy; HIV ϭ human immunodeficiency virus; ICL ϭ idiopathic CD4 lymphocytopenia; iPML ϭ inflammatory PML; IRIS ϭ immune reconstitution inflammatory syndrome; JCE ϭ JCV encephalopathy; JCM ϭ JCV meningitis; JCV ϭ JC virus; JCVGCN ϭ JCV granular cell neuronopathy; mAb ϭ monoclonal antibody; mIns ϭ myo-inositol; MS ϭ multiple sclerosis; MTR ϭ magnetization transfer ratio; NAA ϭ N-acetylaspartate; NIRIS ϭ neuro-IRIS; PCR ϭ polymerase chain reaction; PML ϭ progressive multifocal leukoencephalopathy; PML-IRIS ϭ PML associated with IRIS; RR ϭregulatory region; SLE ϭ systemic lupus erythematosus

Skull base osteomyelitis is a relatively rare condition, generally occurring as a complication of advanced otologic or sinus infection in immunocompromised patients. Skull base osteomyelitis is generally divided into 2 broad categories: typical and atypical. Typical skull base osteomyelitis occurs secondary to uncontrolled infection of the temporal bone region, most often from necrotizing external otitis caused by Pseudomonas aeruginosa in a patient with diabetes. Atypical skull base osteomyelitis occurs in the absence of obvious temporal bone infection or external auditory canal infection. It may be secondary to advanced sinusitis or deep face infection or might occur in the absence of a known local source of infection. Atypical skull base osteomyelitis preferentially affects the central skull base and can be caused by bacterial or fungal infections. Clinically, typical skull base osteomyelitis presents with signs and symptoms of otitis externa or other temporal bone infection. Both typical and atypical forms can produce nonspecific symptoms including headache and fever, and progress to cranial neuropathies and meningitis. Early diagnosis can be difficult both clinically and radiologically, and the diagnosis is often delayed. Radiologic evaluation plays a critical role in the diagnosis of skull base osteomyelitis, with CT and MR imaging serving complementary roles. CT best demonstrates cortical and trabecular destruction of bone. MR imaging is best for determining the overall extent of disease and best demonstrates involvement of marrow space and extraosseous soft tissue. Nuclear medicine studies can also be contributory to diagnosis and follow-up. The goal of this article was to review the basic pathophysiology, clinical findings, and key radiologic features of skull base osteomyelitis. ABBREVIATIONS: ASBO ¼ atypical skull base osteomyelitis; EAC ¼ external auditory canal; Ga-67 ¼ gallium-67 citrate; IgG4 ¼ immunoglobulin G4; Tc99m MDP ¼ technetium Tc99m methylene diphosphonate; NEO ¼ necrotizing external otitis; SBO ¼ skull base osteomyelitis; TSBO ¼ typical skull base osteomyelitis S kull base osteomyelitis (SBO) is a rare, potentially life-threatening infection that can present a diagnostic challenge clinically and radiologically. [1][2][3][4] While reports differ in terminology, there are generally 2 categories of SBO: typical and atypical. Typical SBO (TSBO) is the most common and classically occurs in elderly patients with diabetes as a result of necrotizing external otitis (NEO) caused by Pseudomonas species. (Fig 1). 1,3 Atypical SBO (ASBO), also called central SBO, predominantly involves the basisphenoid and basiocciput and occurs without preceding otologic infection (Fig 2). 2,5 Recognition of SBO is increasing, and it is clear that radiologic evaluation plays a critical role in diagnosis and management. The goal of this article was to review the pathophysiology, clinical presentation, and detailed radiologic findings using multiple modalities including CT, MR imaging, and nuclear medicine.

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Discovery of genetic abnormalities associated with neurodegeneration with brain iron accumulation (NBIA) has led to use of a genetic-based NBIA classification schema. Most NBIA subtypes demonstrate characteristic imaging abnormalities. While clinical diagnosis of NBIA is difficult, analysis of both clinical findings and characteristic imaging abnormalities allows accurate diagnosis of most of the NBIA subtypes. This article reviews recent updates in the genetic, clinical, and imaging findings of NBIA subtypes and provides a practical step-by-step clinicoradiological algorithm toward clinical diagnosis of different NBIA subtypes.