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Background
Cat-scratch disease (CSD) is a bacterial infection caused by Bartonella henselae, usually introduced by a cat scratch or bite. Fleas are a vector for Bartonella among cats, and cats have a high incidence of asymptomatic seropositivity. Kittens cause most human infections because they are more likely to be bacteremic with B. henselae. CSD has a worldwide distribution. About 20,000 cases are reported in the United States annually. Bartonella infection is granulomatous and suppurative. CSD is a common cause of chronic pediatric adenopathy. Most (90%) patients present with painful regional adenopathy of the upper extremity, axilla, or head/neck within 1 - 2 weeks of infection. Systemic symptoms are common. The disease is more widespread in 5 - 10% patients, especially involving liver, spleen, bone, and central nervous system (CNS). Atypical disease is more common in older adults. CSD in immunocompromised patients may present as bacillary angiomatosis-peliosis, characterized by angioproliferative lesions resembling Kaposi sarcoma. CSD is usually diagnosed by clinical presentation and a history of a cat scratch or bite. B. henselae is difficult to culture but serologic testing is available. Lymph node biopsy is not routine. Patients are usually treated conservatively because typical CSD is self-limited. Painful lymph nodes may be aspirated for symptomatic relief. Adenopathy usually resolves in 2 - 4 months although may persist for 1 - 2 years.

Educational Goals / Teaching Points
This educational exhibit provides radiologists and trainees with current knowledge about CSD including its etiology, clinical presentation, and imaging findings of patients from our institutions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Imaging is important for the diagnosis and evaluation of CSD because its nonspecific presentation raises clinical concerns for neoplasia. Often the palpable mass caused by adenopathy is imaged. Affected nodes are hypoechoic on ultrasound and demonstrate T2 hyperintensity, enhancement, and surrounding soft tissue edema by magnetic resonance imaging. Abdominal granulomas are hypoechoic on ultrasound and hypoattenuating on CT. Rim enhancement and calcifications have been reported. Bony lesions are ill-defined, osteolytic, and may have increased radiotracer uptake on bone scans.

Conclusion
CSD is a relatively common bacterial infection. Radiologists may be the first to suggest the diagnosis and prevent unnecessary biopsy and treatment.