|LETTER TO EDITOR
|Year : 2021 | Volume
| Issue : 4 | Page : 262-263
An anatomical model for SARS-CoV-2 entry into mastoid and middle ear in COVID-19 patients
Chiman Kumari1, Bora Ishani2, K Narayan Ravi3, Ashutosh Kumar3
1 Department of Anatomy, Postgraduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Virology, Postgraduate Institute of Medical Education and Research, Chandigarh, India
3 Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar, India
|Date of Submission||05-Mar-2021|
|Date of Acceptance||31-Oct-2021|
|Date of Web Publication||21-Dec-2021|
Dr. Ashutosh Kumar
Department of Anatomy, All India Institute of Medical Sciences, Patna, Bihar
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kumari C, Ishani B, Ravi K N, Kumar A. An anatomical model for SARS-CoV-2 entry into mastoid and middle ear in COVID-19 patients. J Anat Soc India 2021;70:262-3
|How to cite this URL:|
Kumari C, Ishani B, Ravi K N, Kumar A. An anatomical model for SARS-CoV-2 entry into mastoid and middle ear in COVID-19 patients. J Anat Soc India [serial online] 2021 [cited 2022 May 24];70:262-3. Available from: https://www.jasi.org.in/text.asp?2021/70/4/262/333194
Recently, Frazier et al. detected SARS-CoV-2 RNA in the PCR-based testing of postmortem biopsy specimens from the middle ear and mastoid cavity of two out of three COVID-19 patients. Detection of SARS-CoV-2 in the deeper parts of the ear is a finding of utmost clinical significance and deserves extensive deliberation. However, how did SARS-CoV-2 reach these parts of the ear, which are not directly exposed to the external environment, is intriguing and deserves an anatomical explanation. In this letter, we suggest an anatomical model which can effectively explain the route of the viral entry from the nose to the middle ear and to the mastoid.
To invade and replicate into a human tissue, SARS-CoV-2 binds to a human cell surface receptor called angiotensin-converting enzyme 2 (ACE-2) through the receptor-binding domain (RBD) present at its spike (S) protein. For the successful host cell membrane fusion and infectivity, following ACE-2 binding, cleavage of the viral spike protein (S) by the proteases like transmembrane serine protease-2 (TMPRSS-2) is essential. Recent studies showed enriched expression of ACE-2 (and also TMPRSS-2) in the epithelial lining of the upper respiratory tract including the nose in humans. Similar evidence has been found for the epithelial lining of the middle ear and mastoid cavities in a recent mouse study.
The nasopharynx, from where swab is collected for viral testing in COVID-19, is anatomically unique in the sense that it presents a common meeting place for the ear, nose, and mouth cavities. The middle ear opens into the lateral wall of the nasopharynx through the “Eustachian tube (ET)” – an osteocartilaginous canal which is about 36 mm in length [Figure 1]. ET has important functions of draining the mucosal secretions from the middle ear cavity to the throat and maintaining the air pressure in the middle ear cavity allowing the controlled passage of the breathing air through the slit-shaped nasopharyngeal opening of the tube. The middle ear is further connected to the mastoid cavity through a very short passage called aditus [Figure 1]. ET has a lining of the respiratory epithelium, and the middle ear and mastoid cavities have simple squamous secretory epithelium, which may allow them to harbor SARS-CoV-2, owing to abundant expression of the viral cell entry factors., The nasopharynx has a mucosal continuity with the middle ear and mastoid cavity through the ET that presents a convenient route for the spread of the virus to the deep auricular parts [Figure 1].
|Figure 1: A model depicting anatomical route for transmucosal spread of SARS-CoV-2 from the nasopharynx to the middle ear and mastoid cavities. [There is an anatomical continuity from the nasopharynx to the middle ear and then to the mastoid through the Eustachian tube. This route is initially lined by the mucosal respiratory (nasopharynx to the Eustachian tube) epithelium and then secretory simple squamous (middle ear and mastoid) epithelium which express angiotensin-converting enzyme 2 receptors that can bind SARS-CoV-2, hence presents a transmucosal route of spread for entry of the virus while inhaling air through the nose].|
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