Discussion

Of 83 patients eligible for inclusion, 51.8 per cent (n = 43) had evidence of sinus opacification and 24.1 per cent (n = 20) had evidence of middle-ear or mastoid opacification. The median total Lund–Mackay sinus score for all patients was 1.0 (interquartile range = 2.0), and the median middle-ear and mastoid opacification score was 0 (interquartile range = 0). There was no statistically significant difference in sinus or middle-ear and mastoid opacification between patients after stratification based on 30-day all-cause mortality.

Marginally lower rates of sinus and mastoid opacification in patients with Covid-19 are reported in the literature (Table 6);^{Reference Mughal, Charlton and Clark25–Reference İslamoğlu, Ayhan, Bercin, Kalem, Kayaaslan and Güner30} 41.8 per cent of Moonis and colleagues’ cohort of 55 patients had sinus disease, yet only 7 per cent demonstrated mastoid opacification.^{Reference Moonis, Mitchell, Szeto and Lalwani29} Similarly, İslamoğlu et al. reported much lower levels of mastoid opacification in a cohort of 129 patients, at only 2.32 per cent.^{Reference İslamoğlu, Ayhan, Bercin, Kalem, Kayaaslan and Güner30}

Table 6.

Literature review of studies examining incidence of sinus and mastoid and middle-ear opacification

N/A = not applicable

Our results reflect higher levels of sinus opacification in patients with Covid-19 when compared with a 14.8–37 per cent rate of incidental prevalence of sinus opacification on CT prior to the SARS-CoV-2 pandemic.^{Reference Nazri, Bux, Tengku-Kamalden, Ng and Sun26} However, Naeini et al. analysed CT imaging of patients with anosmia secondary to Covid-19 infection, and found that most patients (83.7 per cent) had a Lund–Mackay score of 0, discrediting a conductive pathophysiology for anosmia.^{Reference Naeini, Karimi-Galougahi, Raad, Ghorbani, Taraghi and Haseli27} Similarly, a systematic review of radiological imaging in Covid-19 patients with anosmia, by Keshavarz et al., suggested sinus opacification in only 12.5 per cent.^{Reference Keshavarz, Haseli, Yazdanpanah, Bagheri, Raygani and Karimi-Galougahi28} The pattern of sinus involvement was also variable. Maxillary and ethmoidal sinus involvement predominated in our study, whereas frontal sinus involvement was uncommon. Similarly, ethmoidal, maxillary and sphenoid sinuses were most commonly affected in Moonis and colleagues’ cohort.^{Reference Moonis, Mitchell, Szeto and Lalwani29}

Although the nasopharynx has been demonstrated to host high titres of SARS-CoV-2,^{Reference Sungnak, Huang, Bécavin, Berg, Queen and Litvinukova9,Reference Zou, Ruan, Huang, Liang, Huang and Hong10} literature suggests this is not reflected in radiological findings.^{Reference Moonis, Mitchell, Szeto and Lalwani29,Reference İslamoğlu, Ayhan, Bercin, Kalem, Kayaaslan and Güner30} Moonis et al. further demonstrated that olfactory cleft opacification and nasopharyngeal thickness did not correlate with Covid-19 infection.^{Reference Moonis, Mitchell, Szeto and Lalwani29} Such limited sinonasal involvement does not reflect radiological findings reported for other viral upper respiratory tract infections.^{Reference Gwaltney, Phillips, Miller and Riker31} Moonis et al. also reported minimal radiological evidence of sinusitis secondary to SARS-CoV-2, which correlated with their clinical findings; less than 10 per cent of their study population reported symptoms of upper respiratory tract infection.^{Reference Moonis, Mitchell, Szeto and Lalwani29} Systematic reviews^{Reference Lovato and de Filippis32} and case series^{Reference Huang, Wang, Li, Ren, Zhao and Hu33–Reference Zhang, Dong, Cao, Yuan, Yang and Yan35} suggest sinonasal symptoms are atypical in Covid-19 infection, with lower respiratory tract infection and constitutional symptoms predominating. Reports suggest nasal congestion and rhinorrhoea are less common symptoms,^{Reference Lovato and de Filippis32} in comparison to fever, fatigue, cough and shortness of breath.^{Reference Huang, Wang, Li, Ren, Zhao and Hu33–Reference Zhang, Dong, Cao, Yuan, Yang and Yan35} Although magnetic resonance imaging modalities were beyond the scope of this paper (as they were not available for the patients), other studies have correlated anosmia with loss of olfactory bulb volume, opacification of the olfactory cleft and a T2-weighted fluid-attenuated inversion recovery (‘FLAIR’) hyperintensity of the olfactory tract.^{Reference Laurendon, Radulesco, Mugnier, Gérault, Chagnaud and El Ahmadi36–Reference Strauss, Lantos, Heier, Shatzkes and Phillips38}

Mastoiditis is a frequent incidental radiological finding on CT of the head, as fluid collects in mastoid air cells whilst the patient lies supine as the scan is performed.^{Reference Mughal, Charlton and Clark25} Mughal et al. reported that 8.4 per cent of head CT scans suggested incidental mastoid opacification.^{Reference Mughal, Charlton and Clark25} Acute otitis media is a common sequelae of upper respiratory tract infection,^{Reference Zou, Ruan, Huang, Liang, Huang and Hong10,Reference İslamoğlu, Ayhan, Bercin, Kalem, Kayaaslan and Güner30} with consequent middle-ear effusion and mastoid opacification identifiable on radiological imaging.^{Reference Pitkäranta, Jero, Arruda, Virolainen and Hayden15} Thus, Covid-19 was postulated to manifest as ontological involvement. However, İslamoğlu et al. evaluated temporal CT scans of patients with Covid-19 and found no significant middle-ear or mastoid inflammation,^{Reference İslamoğlu, Ayhan, Bercin, Kalem, Kayaaslan and Güner30} reflecting findings seen in our study, which shows a 24.1 per cent rate of ontological radiological signs.

We recognise that our study has some limitations. A comparator group of coronavirus-negative patients undergoing CT of the head was deemed impractical owing to initially high false negative polymerase chain reaction results.^{Reference Kucirka, Lauer, Laeyendecker, Boon and Lessler39} Whilst Moonis et al.^{Reference Moonis, Mitchell, Szeto and Lalwani29} correlated imaging with patient symptoms, contemporaneous assessment of clinical features was renounced owing to the contagious nature of Covid-19 and concomitant pressures on healthcare workers. Similarly, pure tone audiology would have provided an objective assessment of hearing, but was deemed unfeasible for the purposes of this study as the patients were in isolation and, in some cases, critically unwell.

Images were reviewed by otolaryngologists with prior experience in analysing CT scans of the sinuses and temporal bones. Ideally, imaging findings would be independently corroborated by a second reviewer, or reported by a specialist head and neck radiologist.^{Reference Moonis, Mitchell, Szeto and Lalwani29} Emulating Moonis et al.,^{Reference Moonis, Mitchell, Szeto and Lalwani29} further analysis could have assessed nasopharyngeal thickness and olfactory recess opacification. Intubated patients or those with nasogastric tubes at the time of imaging were not excluded, as cross-sectional imaging was not always sufficiently caudal. Finally, patients who had previously undergone sinus surgery or required prior otological procedures were not excluded from this study.

Although there was no statistical correlation between sinus opacification or middle-ear and mastoid opacification and mortality, there have been no assessments of long-term sequelae. This is pertinent to ENT, with known long coronavirus effects of anosmia^{Reference Walker, Pottinger, Scott and Hopkins40} and sensorineural hearing loss^{Reference Koumpa, Forde and Manjaly17} publicised. Additionally, the statistics presented may prove beneficial when explaining radiological imaging to patients in clinic.

Variable sinus and mastoid and middle-ear opacification may occur between different coronavirus variants. There may be value in repeating this study in another time cohort, to assess whether there is any variation in results with a different viral genotype, or variation in symptoms of otitis media with effusion, hearing loss, rhinosinusitis or Eustachian tube dysfunction.