xRead - Olfactory Disorders (September 2023)

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489

PATEL et al.

TABLE VIII.2 SinusCT Study

Year LOE Study design Study groups

Clinical end point

Conclusions

The obstructive group was characterized by loss of aeration of the OC

Anterior cranial fossa fractures (CT) Aeration of the OC (CT) SS-TDI MRI of olfactory pathways SS-TDI OC aeration pattern (CT) MRI of olfactory pathways CT scan of the paranasal sinuses Assumed diagnosis

Yildirim

2020 3

Prospective cohort

106 patients with OD (41 postinfectious, 13 posttraumatic, 28 idiopathic, and 17 obstructive) 17 normosmic controls 23 patients with persistent COVID-19–related OD

et al 1053

Kandemirli et al 1054

2020 4

Prospective case series

OC opacification was

seen in 73.9% of cases

CT-diagnosed sinonasal disease in 7% patients suspected of nonsinonasal disease One third of patients with suspected sinonasal disease before imaging had normalCT

Mueller

2006 4

Retrospective

137 patients with OD SS-TDI

et al 1056

(sinonasal disease related or not) vs CT-based diagnosis

Biacabe CT scan provided useful information for diagnosing OC syndrome CT = computed tomography; LOE = level of evidence; MRI = magnetic resonance imaging; OC = olfactory cleft; OD = olfactory dysfunction; SS-TDI = Sniffin’ Sticks threshold, discrimination, identification combination. et al 1055 2004 4 Retrospective case series 13 patients with OCdisease Olfactory threshold test Endoscopic evaluation CT scan of the paranasal sinuses

As a major relay of the olfactory pathways, the most studied structure is the OB, which can be easily visualized on MRI without contrast. Indeed, a large number of studies have evaluated its morphology and particularly its volume. The majority of studies (nine prospective cohort studies, six case series, and six retrospective studies) agree that OBV is decreased in patients experi encing a wide range of pathologies affecting OF. 241,253–255, 310,312,917,934,1031,1032,1053,1054,1059–1061,1063,1068,1069,1072–1074 Indeed, patients with posttraumatic, 253,309,310 postinfectious, 253,254 idiopathic, 1032,1053,1061 obstructive, 1053 and congenital 917,1069 OD were found to have smaller OBVs compared with normosmic controls. Several studies (two prospective cohort stud ies, three case series, and four retrospective stud ies) have also found a positive correlation between OBV and OF, 241,253,1030,1031,1061,1071–1073 notably in postinfectious, 241,253,1031 posttraumatic, 253,310,1072,1073 and idiopathic 1061 OD. However, some studies (one prospective cohort study, one case series) found no cor relation between OBV and OF. 1063,1066 In the same vein, it has been described (one prospective cohort study, one retrospective study) that OBV correlates to the results of olfactory ERPs. 1063,1068 Qualitative OD also seems to be associated with OB reduction, since three studies (one prospective cohort study, two retrospective studies) have found that patients with parosmia have smaller OBVs. 253,1031,1072

Structural MRI studies have also investigated the plastic ity of the OB over time. One prospective cohort study found that OBV is inversely correlated to the duration of the olfac tory loss. 254 Another prospective cohort study showed that changes in OF over time is correlated to change in OBV. 1064 Three studies (one case series, two retrospective stud ies) have assessed the prognostic value of the OB. Some authors have found that the OBV and integrity are prognostic factors of recovery in postinfectious 1071 and posttraumatic 1065,1071 olfactory loss. In contrast, others found that the OBV was not an indicator of the prognosis of recovery 1067 in patients with IOD. Another anatomical structure that has been widely investigated is the olfactory sulcus. Olfactory sulcus depth was reported (three prospective cohort studies, one ret rospective study) to be smaller in patients with OD from various origins (postinfectious, 1053 posttraumatic, 1053 idiopathic, 1053 congenital 917,1059,1060,1069 ), while other stud ies found no difference in IOD 1032,1061 (two prospective cohort studies) or PTOD 1066 (one case series). It was also reported in one retrospective study that olfactory sulcus depth was correlated with OF in patients with all causes ofOD. 1030 It also appears from MRI studies that some causes have characteristic imaging features, rendering MRI useful to confirm the etiology of OD. Indeed, it was reliably found that patients with congenital anosmia have a severely hypoplastic or aplastic OB, and a shallow