Evaluation of abdominal fat pad aspiration highlighting challenges to interpretation

Fine-needle aspiration (FNA) of abdominal fibroadipose tissue is a commonly utilized method for the detection of amyloidosis. While generally regarded as an accurate and specific detection method, the sensitivity is variable. The objective of this study was to investigate the performance of fat pad FNAs in detecting amyloidosis relative to other tissue biopsies.

Fat pad FNA results from January 1, 2014, to December 31, 2022, were catalogued. Clinical data including FNA indication were ascertained for each case. The results of any subsequent tissue biopsy/biopsies evaluated for amyloidosis by Congo red staining were also assessed. Challenges to diagnostic interpretation were explored.

A total of 334 fat pad FNAs were identified. The most common indications were peripheral neuropathy (29.3%), cardiomyopathy/heart failure (28.1%), monoclonal gammopathy (27.8%), and multiple myeloma/lymphoplasmacytic lymphoma (21.0%). Cytologic interpretations were: 7 (2.1%) nondiagnostic, 284 (85.0%) negative, 18 (5.4%) indeterminate, 16 (4.8%) suspicious, and 9 (2.7%) positive for amyloid deposition. In our sample, 103 (30.8%) patients had Congo red testing performed on a subsequent surgical specimen(s) including: 3 of 7 of nondiagnostic cases, none which were positive on the subsequent surgical; 70 of 284 negative cases, 27 which were positive on the subsequent surgical; 11 of 18 indeterminate cases, 7 which were positive on the subsequent surgical; 13 of 16 suspicious cases, 2 which were positive on the subsequent surgical; and 6 of 9 positive cases, 3 which were positive on the subsequent surgical. Challenges to FNA interpretation included scant cellularity, focal staining/birefringence, and overstaining.

It is best to view fat pad aspiration versus other tissue biopsy results as complimentary diagnostic tests that should be interpreted in the context of the clinical setting and overall clinical suspicion for amyloidosis.