COVID-19 has been associated with a rise in the incidence of sino-nasal mucormycosis. We discussed the clinical manifestations and MR imaging findings for 62 individuals with sino-nasal mucormycosis in the context of COVID-19.
The present study showed a systematic approach for analyzing sino-nasal mucormycosis on MR imaging in post-COVID-19 patients, enabling a full evaluation of mucormycosis regional involvement and probable sites of extension. Furthermore, it demonstrated different disease imaging spectra.
Patients with post-COVID-19 sino-nasal mucormycosis were observed to have a median age of 50.65 ± 8.25 years, with 63% of them being female. Other research revealed a male-dominated population and a median age of over 55 years.
The most prevalent variant of mucormycosis infection is sino-nasal mucormycosis, which affect 50% of the patients [17]. Patients who are immunosuppressed and diabetic are more likely to develop it [6, 18].
Two meta-analyses found that DM was the primary risk factor for mucormycosis, representing 40% to 64% of cases [19, 20]. In our study, underlying diabetes mellitus as a predisposing factor was reported in 56/62 (90.3%) of mucormycosis cases and history of corticosteroid use was present in 48/62 (77.3%) patients.
According to reports, there can be a lag of 0 to 60 days between the diagnosis of COVID-19 and the onset of sino-nasal mucormycosis [9, 21], which is consistent with our finding that was found to be 25.7 (± 4.6) days.
In our study, the clinical presentation varied. The most common clinical symptoms were headache (52/83.87%) and the least was facial palsy seen in two patients.
Four main mechanisms proposed for the spread of sino-nasal mucormycosis are direct, perineural, perivascular, and hematogenous spread. The clinical manifestations and involved sites in each individual depend on the mode(s) of spread and the extent of involvement by the disease process [22]. Sixty-two (62) patients with mucormycosis had been included in our investigation. Patients initially exhibit sino-nasal involvement which may progress to the orbits, masticator space, face, pterygopalatine fossa, hard palate, maxillary alveolus, zygomatic process, skull base involving the Clivus and pterygoid process, and intracranial extension to involve the cavernous sinus, internal carotid artery, and cerebral hemispheres.
MRI provides more accurate assessment of soft tissue and intra-cranial involvement, invasion of the skull base, perineural dissemination, and vascular obstruction. Due to the iron and manganese in the fungal components, MRI shows varying signal intensity according on the sinus contents [23]. MRI contrast examination reveals invasion of the soft tissues of the orbit, infiltration of the skull base, perineural dissemination, intracranial complications and vascular obstruction involving internal carotid artery. T2 slow flow can predict internal carotid artery invasion by the fungus [24]. In head and neck cancers, particularly adenoid cystic carcinoma, perineural dissemination is seen frequently. Fungal hyphae frequently invade blood vessels and nerves, causing perineural spread and cavernous sinus invasion [25].
MR features of acute fulminant invasive fungal sinusitis (AFIFS) include black turbinate sign, (non-enhancing, hypointense turbinate), variable intensity within the sinuses on T1- and T2-weighted images (primary T2 low signals), obliteration of the nasopharyngeal planes, preantral fat infiltration, loss of contrast enhancement of the sino-nasal mucosa and extraocular muscles, inflammatory changes in the extraocular muscles and fat, and cerebral leptomeningeal enhancement [26, 27]. According to the results of the current study, in post-COVID-19 individuals, all of the previously recognized MRI mucormycosis characteristics were shown to varied degrees and did not differ from those seen in AFIFS.
Fungal infiltration or vascular congestion-related edema are the two main causes of extra-sinus fat infiltration, and as the fungus travels predominantly through perivascular channels, even before bone osteolysis occurs, it takes place [28, 29]. According to Gorovoy et al., distinct but late and less common features of AFIFS included retro-antral fat pad inflammation, osseous erosion, and orbital extension [28]. However, we reported the involvement of the retro-antral fat, facial bones, and orbit in 53.23% (33/62), 12.9% (8/62), and 56.45% (35/62) of our patients, respectively.
The orbit and brain tissues become infected with fungal growth due to direct vascular invasion or embolic seeding [28]. Additionally, Mathur et al. [30] discovered a link between the posterior ethmoid and sphenoid sinus being affected and a higher likelihood of intracranial extension [30].
In our investigation, we found no statistically significant correlation between extra-sinus extension to the orbit and brain and infiltration of the posterior ethmoid and sphenoid sinuses, as well as the maxillo-facial spaces.
The limitations of the present study include its small sample size, so a bigger multicenter cohort with a larger sample size is required to improve the accuracy of the results. Second, lack of an observed association of individual imaging findings with clinical outcomes. Finally, we did not demonstrate a difference in findings between sino-nasal mucormycosis in patients with COVID-19 and in other settings.