Superior Aortic Recess Mimicking Takayasu Arteritis in a Patient With Adult-Onset Still's Disease.

The superior aortic recess, a normal pericardial extension around the ascending aorta, can be misinterpreted as pathological findings on imaging studies, potentially leading to misdiagnosis of conditions such as Takayasu arteritis. We report a case of persistent fever and joint pain initially suspected of having Takayasu arteritis based on contrast-enhanced CT showing apparent aortic wall thickening. Laboratory tests showed elevated inflammatory markers (CRP: 7.07 mg/dL, WBC: 11,200/μL), microcytic anemia (hemoglobin: 7.8 g/dL), and thrombocytosis (platelets: 599,000/μL). Initial treatment with nonsteroidal anti-inflammatory drugs, sulfasalazine, and low-dose prednisolone was ineffective. Although contrast-enhanced CT suggested aortic wall thickening, a fluorodeoxyglucose positron emission tomography scan/CT revealed no uptake in this area, making a diagnosis of Takayasu arteritis unlikely. Radiological reassessment identified the structure as the superior aortic recess rather than aortic wall thickening, and the patient fulfilled Yamaguchi's criteria for adult-onset Still's disease with markedly elevated ferritin (3,459 ng/mL). Treatment with prednisolone 60 mg daily and subsequent addition of tocilizumab 480 mg weekly led to complete symptom resolution and normalization of laboratory parameters. This case highlights the importance of recognizing normal anatomical variants in radiological interpretation to avoid misdiagnosis, emphasizing the need for comprehensive diagnostic approaches incorporating clinical, laboratory, and appropriate imaging findings to distinguish between vascular pathologies and normal anatomical variants.