From the Guidelines

Anosmia is a common indication for Computed Tomography (CT) of the Paranasal Sinuses (PNS) [ 1, 1].

Patients presenting with persistent or recurrent anosmia, particularly in conjunction with other symptoms such as nasal congestion or facial pain, may undergo CT PNS to evaluate for underlying conditions such as chronic sinusitis, nasal polyps, or tumors [ 1, 1].
The CT PNS scan is typically performed without intravenous contrast [ 1, 1], as it provides excellent visualization of the sinuses and surrounding structures.
CT without contrast is the preferred modality for evaluating recurrent acute sinusitis, chronic sinusitis, preoperative for sinus surgery, nasal polyposis, persistent nasal congestion-obstruction, immunocompromised patient with fever, dentomaxillary pain, facial pressure-headache unresponsive to medical therapy, and anosmia after appropriate workup [ 1].
MRI with contrast may be used in certain cases, such as skull base dehiscence with opacification, unilateral sinonasal opacification, sinonasal process with cranial extension, expansile sinonasal mass with bony erosion, sinonasal mass with orbital extension, biopsy-proved tumor, and fungal sinusitis [ 1].
The choice of imaging modality depends on the specific clinical scenario and the suspected underlying condition [ 1, 1].

From the Research

Anosmia, or the loss of smell, can be caused by various factors, including COVID-19, trauma, chronic sinusitis, and neoplasms 2.
The use of Computed Tomography (CT) scans of the Paranasal Sinuses (PNS) in the diagnosis of anosmia has been studied, particularly in the context of COVID-19 3, 4.
A study published in 2023 found that PNS CT findings were significant in patients with COVID-19 who experienced a loss of smell, and were associated with the degree of loss of smell 3.
However, another study published in 2021 noted that routine imaging, including CT scans, was not typically used to primarily diagnose smell loss, and that validated orthonasal smell tests should be part of the workup of patients with suspected olfactory dysfunction 2.

The diagnostic evaluation of anosmia typically involves a thorough history and physical, as well as validated orthonasal smell tests, such as the Sniffin' Sticks and the UPSIT 2.
Imaging modalities, including MRI and CT, may be used in the workup of olfactory dysfunction, but the criteria for their use are heterogeneous 2.
A study published in 2022 found that blood parameters, such as neutrophil and lymphocyte counts, may be useful in detecting loss of smell in patients with COVID-19 4.

Anosmia is a common symptom of COVID-19, with a prevalence of 24.82% in one study 5.
The prevalence of anosmia in COVID-19 patients may be associated with factors such as male sex, history of recent travel, smoking, and severe course of the disease 5.
A study published in 2017 noted that anosmia can have a profound negative impact on quality of life, and that efforts should focus on improving diagnosis and treatment outcomes for olfactory dysfunction 6.