Imaging findings of Rhino-Orbito-Cerebral Mucormycosis in a COVID-19 patient

A 40-year old man presented with facial swelling and redness of left eye, clinical examination shows blackening and ulceration of left nasal turbinates. He is a known case of poorly controlled diabetes mellitus on treatment. The reverse transcriptase-polymerase chain reaction from nasopharyngeal swab tested positive for SARS CoV-2 virus.

CT scan showed polypoidal mucosal thickening and hyperdense foci within left maxillary, ethmoid, sphenoid and frontal sinuses and sinus wall erosions. MRI contrast study revealed diffuse nodular mucosal enhancement within the sinuses and non-enhancement of left nasal turbinates (black turbinate sign) [1]. There is perineural extension along infraorbital nerve and inflammation of inferior rectus muscle. There is peri-antral soft tissue infiltration with involvement of infratemporal fossa, pterygopalatine fossa and masticator space. Enhancing lesion is noted at left orbital apex, foramen rotundum and cavernous sinus with narrowing of left internal carotid artery suggesting angioinvasion. Necrotizing cellulitis changes were noted in facial muscles and premaxillary fat. T2/FLAIR hyperintense area showing diffusion restriction is noted in the left basi-temporal lobe with adjacent meningeal enhancement. Altered signal intensity is seen involving skull base marrow suggesting infiltration.

Rhino-orbito-cerebral mucormycosis (ROCM) is considered as a rare invasive infection caused by class phycomycetes fungi involving immunocompromised patients, arising from nasal and sinus mucosa, spreads rapidly to orbit and brain. Extensive angioinvasion is considered as the main cause leading to vascular thrombosis and tissue necrosis[7]. Vascular involvement is more common cause of high morbidity and mortality,infiltrating cavernous sinus and orbital apex leading to cellulitis of face, loss of vision..Intracranial involvement can cause narrowing of internal carotid artery leading to ischemic infarcts[3]. Meningeal involvement can be seen.

Imaging helps in diagnosis of ROCM to evaluate the extent of disease plays a crucial role in early diagnosis and timely intervention. CT scan demonstrates nodular mucosal thickening with absence of fluid levels and hyperdense content leading to erosions of bony sinus walls.

MRI provides better evaluation of intracranial and soft tissue involvement, skull base invasion, perineural spread and vascular obstruction. MRI demonstrates variable signal intensity depending on the sinus contents, due to iron and manganese in the fungal elements[2].MRI contrast study shows invasion of orbital soft tissues, skull base infiltration, perineural spread , intracranial complications and vascular obstruction involving internal carotid artery.T2 slow flow can suggest internal carotid artery invasion by the fungus[3].

Perineural spread is most commonly seen in head and neck malignancies more often seen in adenoid cystic carcinoma. Fungal hyphae tend to involve nerves and vessel wall leading to perineural spread and cavernous sinus invasion[4].

In our case, perineural spread is seen along infraorbital nerve extending from floor of orbit into cavernous sinus and foramen rotundum noted.  The patient developed symptoms after 20 days of admission for COVID-19, during which he was on broad-spectrum antibiotics and steroids and this is considered as an aggrevating factor in our case, COVID-19 may lead to secondary infection primarily causing immune dysregulation[6]. Clinicians should be aware of secondary invasive fungal infections as a complication in COVID-19 patients.

ROCM is considered as an emerging rapidly disseminating fungal infection when associated with immunocompromised conditions and carry fatal prognosis with cavernous sinus involvement[5]. Hence, radiologists should evaluate the extension and involvement of invasive fungal sinusitis which can lead to early diagnosis and timely management with antifungal agents and surgical debridement further helps to reduce morbidity and mortality.

Histopathological follow up showed fungal elements on KOH mount. A biopsy was taken from left middle turbinated and demonstrated fungal granulomatous inflammation with broad aseptate fungal hyphae on PAS staining suggesting  Mucor species.