key: cord-0058857-ygorumin authors: Shaikh, Sikandar title: PET-CT in Viral Infections date: 2020-12-08 journal: PET-CT in Infection and Inflammation DOI: 10.1007/978-981-15-9801-2_18 sha: 130ee39cb0dbc361562f65f462b428c4947300d8 doc_id: 58857 cord_uid: ygorumin Viral infections are an important clinical entity with varied clinical symptoms and significant overlap with bacterial symptoms. However, some viral conditions have nonspecific symptoms which can be severe enough to cause septicemia. Viral infections involve all the age groups with common symptoms like fever, common cold, GI symptoms like vomiting, diarrhea, neurological symptoms like headache, confusion, irritation, loss of consciousness. The specific pathological entity has to be defined and differentiated. PET-CT in viral infections is having a significant role in evaluating the amount or extent of disease, disease burden, disease involvement, and severity of the disease in the affected organs which is quantified by the SUV max value [1] . However, PET-CT cannot differentiate the exact cause and cannot differentiate in the varied overlap findings in malignant and benign conditions [2] . This has relevance in relation to meningitis/encephalitis which can be viral or bacterial or other causes of meningitis. The basic principle of FDG PET is to demonstrate the increased uptake associated findings of nodal involvement, monitoring disease progression, and monitoring response to treatment [3, 4] . The pathological basis of this is a virus infects the body which activates neutrophils, monocytes, and T cells by releasing local chemokines. Thus, in active inflammation, the activated neutrophils are dependent on anaerobic glycolysis requiring increased glucose which is directly proportional to high FDG uptake. Other cell granulocytes and macrophages also play an important role in facilitating glucose transport in chronic conditions. Thus, FDG uptake is directly proportional to the amount of active inflammation. Subacute Sclerosing Panencephalitis (SSPE) is one of the important components of the neurodegenerative disease [5] . This has features of cognitive and behavioral changes, atonic and/or myoclonic seizures, periodic paroxysms on electroencephalogram (EEG), and increased measles antibodies in cerebrospinal fluid. SSPE is one of the dreadful forms of disease which is caused by the reactivation of the measles virus in the brain for several years after the episode of the primary measles infection. Although it has been studied for many years, its pathogenesis and treatment have not been elucidated. FDG PET-CT is now evolving as an important imaging modality for SSPE [6] . One of the studies by Yeong Seon et al. proved that cortical glucose metabolism is significantly reduced in patients with SSPE, but some of them are normal [7] . The immune system is involved in this pathogenesis. The pattern of FDG PET-CT shows variable uptake patterns depending on the various locations during viral exposure. CNS's presentations are of meningitis, encephalitis, dural enhancement, gyral enhancement and combination of any of this with or without cerebral edema (Figs. 18.1 and 18.2). Upper respiratory tract infection is one of the most common infections. This includes the varied conditions like rhinitis, sinusitis, ear infections, acute pharyngitis, tonsillitis, epiglottitis, and various infections. Laryngitis is one of the important components of the upper respiratory tract involvement. The amount of FDG uptake is directly proportional to the amount and acuteness of infectivity [8] [9] [10] [11] . Acute pharyngitis is one of the important viral infections in young children. Various mild changes due to clinical sysmptoms are important for the evalaution. Acute pharyngitis is caused by viruses in more than 70% of cases in young children. Mild pharyngeal redness and swelling and tonsil enlargement are typical. Streptococcal infection is rare in children under five and more common in older children. In countries with crowded living conditions and populations that may have a genetic predisposition, post-streptococcal sequelae such as acute rheumatic fever and carditis are common in school-age children but may also occur in those under five. Acute pharyngitis in conjunction with the development of a membrane on the throat is nearly always caused by Corynebacterium diphtheriae in developing countries. However, with the almost universal vaccination of infants with the DTP (diphtheria-tetanus-pertussis) vaccine, diphtheria is rare. FDG PET-CT plays an important role in the evaluation of pharyngitis. The amount of uptake is directly proportional to the amount of inflammation [12, 13] . The pathogenesis is similar to other causes. However, bilateral consolidations predominantly peripheral with air bronchogram and pulmonary vessel cut off sign are the hallmark presentations on CT. These findings are clinically consistent with ARDS. A couple of studies on COVID-19 FDG uptake showed the multiorgan involvement with damage especially to GI tract, kidneys, bone marrow, heart, and a b c d In early and acute stages, no specific classical findings are there in the GI tract. Liver is one of the commonest organs involved in viral hepatitis especially commonly by Hepatitis-B, Hepatitis-A and C. The FDG presentation depends on the a b c d . Early stage no change, acute or chronic stage diffuse increased uptake in the liver secondary to Hepatitis, chronic and delayed stages where liver progresses to chronic liver disease or cirrhosis of liver or further may be predisposing to hepatocellular carcinoma. Here FDG PET-CT evaluates the extent of the disease and response to the treatment especially in acute stages which are reversible [12, [18] [19] [20] [21] . The other presentations are mild peritoneal thickening. The next common organ involved are the genital organs, cervix in female and penis in male. Ca cervix is due to various predisposing factors and one of them is by various viral infections [22, 23] . The carcinoma penis is one of the predisposing factors caused by HPV (human papilloma virus) [24, 25] . Thus, FDG PET-CT plays an important role in the evaluation of viral infections to detect, extent disease involvement, monitoring disease progression, and treatment outcomes. There are lots of research going on especially in COVID-19 PET-CT evaluation. The findings mentioned in our chapter are based on preliminary research. FHPG): a potential imaging agent of viral infection and gene therapy using PET Differentiation of malignant from benign solitary pulmonary lesions using chest radiography, spiral CT and HRCT The basic principles of FDG-PET/CT imaging The Pivotal Role of FDG-PET/CT in Modern Medicine Diagnosis and treatment of viral encephalitis A correlative study of FDG PET, MRI/CT, electroencephalography, and clinical features in subacute sclerosing panencephalitis 18F-FDG PET and MRS of the early stages of subacute sclerosing panencephalitis in a child with a normal initial MRI. Pediatr Radio Whole-body positron emission tomography: normal variations, pitfalls, and technical considerations Atlas of confounding factors in head and neck PET/CT imaging Positron emission tomography as a diagnostic tool in infection: present role and future possibilities F-18-fluorodeoxyglucose positron emission tomography combined with CT in critically ill patients with suspected infection EANM/SNMMI guideline for 18F-FDG use in inflammation and infection FDG PET/CT in infection and inflammation current and emerging clinical applications A potential role for F-18 FDG PET/CT in evaluation and management of fibrosing mediastinitis PET/CT in non-oncological lung diseases: current applications and future perspectives 18)F]-FDG lymphoid tissue kinetics to characterize nonhuman primate immune response to Middle East respiratory syndrome-coronavirus aerosol challenge 18 F-FDG PET/CT findings of COVID-19: a series of four highly suspected cases A unique presentation of appendicitis: F-18 FDG PET/CT European Association for the Study of the Liver. EASL clinical practice guidelines on the management of ascites, spontaneous bacterial peritonitis, and hepatorenal syndrome in cirrhosis Ascites metabolism measurement enhanced the diagnostic value and accuracy of prognostic evaluation in 18 F-FDG PET/CT studies in malignant ascites patients Use of 18F-FDG PET to predict tumor progression and survival in patients with intermediate hepatocellular carcinoma treated by trans-arterial chemo-embolization Prevalence of genital human papillomavirus among females in the United States, the National Health and Nutrition Examination Survey The standardized uptake value for F-18 fluorodeoxyglucose is a sensitive predictive biomarker for cervical cancer treatment response and survival Herzog 18F-FDG PET/CT for staging of penile cancer The role of PET/CT imaging in penile cancer