Lung Abscess in a Cat Successfully Treated without Surgery: Diagnostic Imaging Features

Background: Lung abscesses occur when the lung tissue necrotises due to various causes, such as bacterial infection, foreign bodies, or tumours, resulting in a pus-filled a cavity that forms a mass. Only one previous case of medical treatment for a lung abscess in cats has been reported, making it difficult to establish a well-defined treatment protocol. This report aimed to describe the radiographic, B-mode ultrasound, and computed tomography (CT) imaging features of lung abscesses, as well as the cytology and medical treatment involved. Case: A 11-year-old spayed female Persian cat was referred to the hospital with lethargy and frequent white, foamy vomiting. The patient had a preexisting chronic kidney disease and was under ongoing management. Thoracic radiographs revealed an opaque soft tissue opacity mass in the left caudal lung lobe. Further imaging was performed to determine the nature of a suspected tumour mass. Lung ultrasonography showed a mass with a cavity containing anechoic fluid within consolidated lung parenchyma. Computed tomography imaging further revealed a well-defined mass with a central cystic lesion containing gas and peripheral contrast enhancement. Fine-needle aspiration was successfully performed under ultrasound guidance without causing pneumothorax, revealing the presence of bacteria and neutrophils and leading to the diagnosis of a lung abscess. The fine-needle aspiration results strongly suggested inflammation rather than a tumour; therefore, antibiotic treatment was initiated. Initially, doxycycline and clindamycin, which had been used in previously reported cases, were administered; however, persistent diarrhoea developed after 2 days. Doxycycline, known to cause gastrointestinal tract toxicity potentially, was then replaced with amoxicillin and clavulanate. The cat’s clinical signs improved with antibiotic treatment, and the lung mass gradually decreased in size, resolving completely after 6 months without surgical intervention. Discussion: This report describes typical features of lung abscesses observed using radiography, B-mode ultrasonography, and computed tomography. Each diagnostic imaging modality has its own advantages and disadvantages. Although lung ultrasonography and computed tomography are more advanced than radiography and can provide detailed information about lesions, they are not suitable for follow-up. Ultrasonography, though useful for obtaining cross-sectional views of the mass, is highly operator-dependent, making accurate monitoring of lesion size challenging. Computed tomography, the most advanced modality, requires general anaesthesia, which poses concerns for patients at risk of anaesthesia-related complications. Additionally, due to the higher radiation exposure compared with other modalities, performing multiple scans at short intervals is not feasible. Therefore, radiography remains the most effective tool for assessing size changes and treatment responses of such masses. Lung ultrasonography can be helpful for providing more detailed information on lesions in cases where computed tomography imaging is not feasible. In human medicine, medical management is the primary treatment option for lung abscesses. However, in veterinary medicine, only 1 case reported to date has been treated solely with medical management without surgical intervention. This case report describes a lung abscess that was successfully treated with medical management alone. It also raises the possibility of chronic kidney disease as an underlying cause of lung abscesses, which would require further research with larger sample sizes and systematic studies to investigate and confirm. Therefore, this case report documents the radiological features of a lung abscess, as observed using radiography, ultrasound, and computed tomography, as well as its medical management and potential underlying aetiology. Keywords: chronic kidney disease, diagnostic imaging, fine-needle aspiration, lung abscess, lung ultrasound, radiography.