A critical reappraisal of the carotid sinus and carotid bulb: Distinguishing neurohistological function from vascular geometry

For over a century, the terms "carotid bulb" and "carotid sinus" have been used inconsistently across anatomy, imaging, and clinical practice, resulting in terminological ambiguity with implications for diagnostic reporting and procedural communication. This review establishes that these are distinct, non-equivalent entities, and that their conflation undermines diagnostic precision and procedural safety. The carotid bulb (CB) is a variable geometric dilation of the carotid bifurcation, defined by luminal expansion and hemodynamic significance. Its fusiform widening creates regions of low, oscillatory wall shear stress that predispose to atherosclerotic plaque formation along the posterolateral internal carotid artery. In contrast, the carotid sinus (CS) is a neurohistological construct, a specialized baroreceptor field concentrated predominantly on the medial wall of the proximal internal carotid artery. These mechanosensitive nerve terminals transduce circumferential wall strain into arterial pressure signals, forming the afferent limb of the baroreflex arc. Critically, the CB and CS exhibit spatial dissociation: baroreceptors are concentrated medially, where hemodynamic forces are benign, whereas atherosclerotic disease develops posterolaterally, where flow disturbance is maximal. Immunohistochemical mapping confirms that baroreceptor density does not correlate with CB geometry. This mismatch explains variable hemodynamic responses during carotid interventions and the failure of imaging-based anatomical landmarks to predict baroreflex function. The clinical consequences are tangible: conflated terminology obscures dual pathology in risk stratification, complicates surgical planning during carotid endarterectomy and stenting, and undermines precision in baroreflex activation therapy. We advocate for systematic adoption of function-based terminology: "carotid bulb" for geometric features, and "carotid sinus" strictly for the neural receptor zone.