The depth of the olfactory sulcus is an indicator of congenital anosmia

Background and Purpose: In congenital anosmia, the olfactory bulb and olfactory tract can be both aplastic or hypoplastic. In clinical routine they are sometimes difficult to assess. We thus want to investigate morphologic differences of the olfactory sulcus in patients with isolated anosmia (IA) since birth or early childhood in comparison to controls in a large group of subjects; to investigate whether the depth of the olfactory sulcus (OS) indicates IA. Materials and Methods: Within the context of a two-center study we investigated 36 IA patients in comparison to 40 controls. Imaging was performed with a standard quadrature head coil (1.5 T; T1 and T2-weighted spin echo sequences were used (coronal plane perpendicular to frontal skull base). We assessed olfactory bulb volume by planimetric contouring, and OS depth in the plane of the posterior tangent through the eyeballs (PPTE). Results: Looking at the OS depth in the PPTE, none of the healthy controls exhibited a depth of less than 8 mm. In IA patients, 10 had an OS deeper than 8 mm, while 26 had OS depth lower than 8 mm. Thus, if we consider an OS depth lower than 8 mm it clearly indicates IA, with a specificity of 1 while the sensitivity is 0.72. Conclusions: In IA, the OS depth in the PPTE is a useful clinical indicator. Indeed, if it is ≤ 8 mm, it clearly indicates IA, with a specificity of 1. If it is deeper, the measure does not clearly predict IA