Non-A, non-B aortic arch dissection with atypical presentation, ambiguous CTA findings, and therapeutic dilemma.

Acute aortic syndrome (AAS) is a potentially fatal vascular emergency in which prompt diagnosis and early intervention are critical to reducing morbidity and mortality. Computed tomography angiography (CTA) is the first-line imaging modality because of its rapid acquisition, wide availability, and high diagnostic accuracy. However, AAS may present with atypical clinical features and subtle imaging findings, creating significant diagnostic and therapeutic uncertainty. We report a challenging case of a 50-year-old woman who presented with chest pain, headache, and hypertensive crisis. CTA demonstrated a thin focal intimal abnormality along the lateral wall of the aortic arch without involvement of the ascending or descending aorta and no clearly defined true or false lumen. However, subsequent multidisciplinary review favored a penetrating atherosclerotic ulcer with associated localized intramural hematoma. The patient was managed conservatively with anti-impulse therapy and serial CTA surveillance, which demonstrated lesion stability followed by complete radiographic resolution on follow-up gated CTA. This case highlights the diagnostic and therapeutic challenges encountered by emergency physicians when evaluating AAS. Atypical clinical features, subtle CTA abnormalities, and uncertainty regarding lesion classification may complicate timely diagnosis and management decisions. The case also illustrates the potential for differing specialist interpretations when imaging findings are equivocal and the value of serial imaging in guiding diagnosis and treatment. Emergency physicians should maintain a high index of suspicion for AAS despite atypical clinical or imaging findings and initiate appropriate anti-impulse therapy and specialist consultation when clinically indicated to minimize missed or delayed diagnoses.