MR evaluation in patients with isolated anosmia since birth or early childhood

Abstract

Background and purpose: Anosmias with chromosomal disorders has been well investigated. However, isolated anosmia (IA) has received less attention, although it occurs more frequently. We compared frontobasal structures in patients with IA since birth or early childhood with those in control subjects.

Methods: Imaging findings obtained in 16 patients with IA were compared with those obtained in eight control subjects. Imaging was performed with a standard quadrature head coil at 1.5 T. T1-weighted spin-echo (coronal plane perpendicular to frontal skull base; section thickness, 3 mm; pixels, 0.43 x 0.39 mm) and sagittal T1-weighted magnetization-prepared rapid gradient-echo (voxels, 1.0 x 1.0 x 1.0 mm) sequences were performed. We assessed the length and depth of the olfactory sulcus, olfactory bulb volume, and olfactory sulcus depth in the plane of the posterior tangent through the eyeballs (PPTE).

Results: Five patients with IA had bilateral hypoplastic olfactory bulbs. Three patients with IA had hypoplastic olfactory bulbs on the right and aplastic olfactory bulbs on the left. Eight patients with IA had bilaterally aplastic olfactory bulbs. The depth of the olfactory sulcus at the level of the PPTE was smaller in patients with IA than in control subjects. The depth of the olfactory sulcus was greater on the right than on the left, and there was no overlap. Among patients with IA, the depth of the olfactory sulcus differed significantly between those with and those without visible olfactory tracts.

Conclusion: The depth of the olfactory sulcus at the level of the PPTE reflects the presence of olfactory tracts. The presence or absence of the olfactory tract may therefore have some association with cortical growth of the olfactory sulcus region. The olfactory sulcus is deeper on the right than on the left, particularly in patients with IA. We speculate that olfaction may be processed predominantly in the right hemisphere.

Fig 1.

Transverse reformation of a 3D data set of an MP-RAGE image. The eyeballs and olfactory bulbs are visible. The coronal plane indicates position of the plane of the PPTE. Note that in normosmic subjects with normal olfactory bulb, this plane cuts through the olfactory bulb.

Fig 2.

Coronal T1-weighted SE image in the PPTE in a healthy subject. Note visualization of the olfactory bulbs and normal development of the olfactory sulci.

Fig 3.

Coronal T1-weighted SE image in the PPTE in a patient with bilateral aplasia of the olfactory bulb, visible olfactory tracts (arrowheads), and slightly flattened olfactory sulci. Note partial volume effect of the right eyeball.

Fig 4.

Coronal T1-weighted SE image in the PPTE in a patient with absent olfactory tracts and sulci. Note partial volume effects of both eyeballs.

Fig 5.

Patient with olfactory tract present only on the right. A, Coronal T1-weighted SE dorsal image in the PPTE. Olfactory tract is visible on the right (arrowhead). There is accordingly different development of the olfactory sulcus, as shown in B. B, Transverse reformation of a 3D data set of an MP-RAGE image in the same patient. Olfactory tract on the left is absent; olfactory tract on the right is visible. Accordingly the olfactory sulcus is shorter (arrowhead) on the left where the olfactory tract is not detectable. Note exact transverse reformation as identified by symmetrical display of periorbital fat and the middle cerebral arteries.

Fig 6.

Olfactory sulcus (OS) depth in PPTE in patients with IA compared with that in healthy controls (means, SEM). Only olfactory sulcus depths greater than 0 were taken into consideration. The olfactory sulcus was significantly deeper on the right than on the left.

Fig 7.

Olfactory sulcus (OS) depth in the PPTE in IA patients with visible olfactory tracts (VOT) and in those with nonvisible olfactory tracts (NOT). There is no overlap between the two groups in terms of olfactory sulcus depth.