key: cord-0919315-pqnkguyd authors: Pruidze, Paata; Mincheva, Plamena; Weninger, Jeremias T.; Reissig, Lukas F.; Hainfellner, Andreas; Weninger, Wolfgang J. title: Performing nasopharyngeal swabs—Guidelines based on an anatomical study date: 2021-07-13 journal: Clin Anat DOI: 10.1002/ca.23762 sha: 053ac680ff057ba99e103d257f8b0635b9092438 doc_id: 919315 cord_uid: pqnkguyd Nasopharyngeal swabs are performed to collect material for diagnosing diseases affecting the respiratory system, such as Covid‐19. Yet, no systematic anatomical study defines concrete prerequisites for successfully targeting the nasopharyngeal mucosa. We therefore aim at simulating nasopharyngeal swabs in human body donors to characterize parameters allowing and supporting to enter the nasopharynx with a swab, while avoiding endangering the cribriform plate. With the aid of metal probes and commercial swabs a total of 314 nasopharyngeal swabs in anatomical head/neck specimens stemming from 157 body donors were simulated. Important anatomical parameters were photo‐documented and measured. We provide information on angles and distances between prominent anatomical landmarks and particularly important positions the probe occupies during its advancement through the nares to the upper and lower parts of the nasopharynx and cribriform plate. Based on these data we suggest a simple and safe three‐step procedure for conducting nasopharyngeal swabs. In addition, we define easily recognizable signals for its correct performance. Evaluations prove that this procedure in all specimens without deformations of the nasal cavity allows the swab to enter the nasopharynx, whereas a widespread used alternative only succeeds in less than 50%. Our data will be the key for the successful collection of nasopharyngeal material for detecting and characterizing pathogens, such as SARS‐CoV‐2, which have a high affinity to pharyngeal mucosa. They demonstrate that the danger for damaging the cribriform plate or olfactory mucosa with swabs is unlikely, but potentially higher when performing nasal swabs. Material from the mucosa of the nasopharynx is collected by means of nasopharyngeal swabs. The procedure is very simple and chiefly used for diagnosing and characterizing suspect respiratory infections (Babady et al., 2018; Gritzfeld et al., 2011; Kaufman et al., 2020; Lieberman et al., 2006; Wang et al., 2020) . Recently the method has attracted enormous attention, since it is used to collect material for testing for and characterizing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes Covid-19 (CDC, 2020; Mawaddah et al., 2020; Piras et al., 2020; Seo et al., 2020; WHO, 2020; Zou et al., 2020) . A long shaft, made of wood, plastic, or similar materials with a tip covered in polyester, rayon, cotton wool, or flocked nylon is inserted into one of the nares. Its tip is then pushed posteriorly through the nasal cavity and the choana to the backside of the pharynx. Here mucus and mucosal cells are collected by swabbing with the material covering the tip. For educating medics and paramedical staff to perform nasopharyngeal swabs, a large number of videos, pictograms, schematic representations, and verbal descriptions were made available in modern digital media (CDC, 2020; Falcone, 2020; Kaufman et al., 2020; Marty et al., 2020; NMC, 2020; Pondaven-Letourmy et al., 2020; Sananès et al., 2020) . They are based on traditional representations of the upper respiratory tract as displayed in anatomical and clinical textbooks (Drake et al., 2015; Logan et al., 2016; Netter, 2019; Sobotta et al., 2008) . For estimating the position and topology of the palate, choana, and nasopharynx from external and thus for guiding the direction in which a swab has to be inserted and advanced, simple anatomical landmarks were suggested. The most important is the ear and the opening of the external acoustic meatus (CDC, 2020; Falcone, 2020; Marty et al., 2020; NMC, 2020) and it is advised to insert swabs toward these structures for a depth of 7-10 cm (Falcone, 2020; NMC, 2020; Pondaven-Letourmy et al., 2020) . The widespread availability of guides describing the swab procedure is in strong contrast to the lack of a sound anatomical justification of potential insertion directions. We therefore set out to carefully characterize and evaluate important landmarks and parameters required for guiding correct and successful advancement of a swab to the nasopharynx. In addition, we aimed at objectively defining the precise direction, in which a swab should be arranged to directly target the nasopharyngeal mucosa without endangering the cribriform plate of the ethmoid bone. Both sides of 157 (85 females, 72 males) head/neck specimens, severed from the bodies of human body donors at the atlanto-occipital transition, were examined. Mean age at time of death was 82 years (50-108). All specimens were derived from Caucasians. They were perfused with 1% formaldehyde/4% carbol for an average of 12-16 h, immersed in 2% formaldehyde/2% carbol for at least 8 months and then pre-dissected during students' dissection classes. In and SPSS (IBM, Version 26.0). Student's t-test was used for assessment of differences in measurement between the left and right sides of specimens (paired) as well as sex-specific variability (independent). All tests were two-tailed at α = 0.05, and the Bonferroni correction was applied in case of multiple testing. The study was in accordance with the declaration of Helsinki and local ethic regulations. All specimens were obtained from body donors, who volunteered and gave written consent to donate their dead bodies to the Division of Anatomy of the Medical University of Vienna for teaching and science prior to decease. In 152 of the 157 head/neck specimens the tip of the probe was successfully and smoothly advanced through the nares and the choana and touched the posterior wall of the pharynx. In 2 (1.27%, 1 female and 1 male) the advancement of the probe/swab was blocked bilaterally, and in 3 (1.91%, 1 female and 2 males) unilaterally (once on the right and twice on the left). These specimens were excluded from statistics. This might be sufficient for a small spectrum of pathologic agents (Rawlings et al., 2013; Ylikoski et al., 1989 ). Yet, it is less sufficient than collecting nasopharyngeal material for pathogens having a high affinity to pharynx mucosa, such as SARS-CoV-2, Epstein-Barr-Virus, and many others (Babady et al., 2018; Yao et al., 1985) . The sensitivity in diagnosing such pathogens is higher if material is collected from the oro-or nasopharynx Heikkinen et al., 2002; LeBlanc et al., 2020; Péré et al., 2020; Vlek et al., 2021) . It is therefore of utmost importance to gain precise knowledge of the anatomy of the upper airways to correctly and unquestionably collect pharynx material by means of nasopharyngeal swabs. Our simulations of 314 nasopharyngeal swabs provide valuable parameters, such as angles and distances in respect to easily identifiable anatomical landmarks and orienting lines. As the most important one we consider the line between nasion und subnasale, since it defines a near coronal plane that is perceived as a "plane representing the face". Of almost equal importance is the often-suggested line between subnasale and tragus, which provides a fairly good estimation of hard palate orientation from outside. However, as our data reveal, suggestions to use the tragus as a landmark for estimating the direction to advance swabs (Marty et al., 2020) , although highly valuable, are only half the message. Our simulations demonstrate that advancement of a swab along the subnasale/tragus line merely in 44.1% succeeds in entering the pharynx. Advancing a swab, while keeping strict contact with the hard palate directs it in an angle of up to 18 (95% interval: 3 -17 ) below this line. Hence advancing the swab in an angle of 18 would always be successful in directing its tip into the lower parts of the nasopharynx. However, our measurements also show that advancement in an angle of 14 is acceptable as well, since it permits at least penetration pharyngis. Therefore, if using the subnasale/tragus line as a guide, we suggest to advance the swab in an angle of 14 below this line until its tip touches the hard palate and then use the hard palate to guide further advancement. We therefore conclude that, independent from anatomical landmarks and orientation lines, the most secure way to successfully perform nasopharyngeal swabs is to advance the swab by keeping constant contact with the hard palate and, ideally, the adjacent septum nasi. In all examined specimens this required pushing the lower rim of the ala nasi slightly upwards with the shaft of the swab. Thus, upward movement of the ala nasi is a simple and easily visible sign for correct swab advancement. As a result of our measurements and analyses, our study now provides three essential lessons for correctly and successfully performing nasopharyngeal swabs ( Figure 5 ): 1. Start with inserting the swab in a steep upward angle for approximately 1 cm into the nares. 2. Push the shaft of the swab upwards, while further advancing, until the tip touches the hard palate and the ala nasi is slightly elevated. 3. Advance the swab by constantly keeping contact with the hard palate until feeling the resistance of the backside wall of the nasopharynx. As an additional visual control, keep sure that the ala nasi is slightly elevated and advance as if targeting an area below the tragus. In 7 of the 314 nasopharyngeal swab simulations, we were unable to advance the probe toward the choana, because of protrusions from the hard palate, which effectively blocked the way along the lower nasal meatus. In 2 head/neck specimens this was bilaterally. In those individuals performing nasopharyngeal swabs would have been entirely impossible. Sceptics of Covid-19 tests quite often argue that during the collection of material from the nasopharynx or nasal cavity, the tips of swabs might end up inside the cranial cavity and destroy basal parts of the forebrain (Sullivan et al., 2020) . The cribriform plate is blamed as potential entry point. Although the cribriform plate is a very thin osseous structure (Figure 1(H) ), we consider it as extremely unlikely to penetrate it with commercial kits for nasopharyngeal swabs. Nevertheless, we decided to make use of the half specimens for researching how a swab has to be advanced to put the cribriform plate in danger. As expected the angle in respect to the subnasale/nasion line is rather steep, and it is similar to the angle in which we suggest the swab should be inserted into the nose for 1 cm when starting a nasopharyngeal swab. Yet, we consider it extremely unlikely that educated F I G U R E 5 Simulation of a secure and successful nasopharyngeal swab in a mediansagittally sectioned head/ neck specimen. (A, B) Swab inserted 1.1 cm following the soft tissue cushion laterally to the subnasale. (C, D) Elevated and advanced swab touching the hard palate with its tip. Note the relation of shaft and ala nasi. (E, F) Swab advanced through the lower rim of choana and touching the posterior wall of nasopharynx. Scale bars, 2 cm personnel will try to advance the swab in such an angle and, if such an angle is accidentally used, it is highly unlikely that the swab is pushed strongly enough to penetrate the cribriform plate. It is more likely that in such a case the swab causes an irritation of the olfactory mucosa and the olfactory nerve, which might result in temporary reduction of olfaction. Our study focuses on simulating nasopharyngeal swabs and defining important anatomical parameters. However, our results also have strong impact on collecting material from the nasal cavity. Since it is considered that also non-medicals and children can perform nasal swabs, they recently became trendy for self-testing for SARS-CoV-2 infections (Péré et al., 2020) . The swabs are suggested to be inserted in a steep upward angle (BMBWF, 2021), which roughly directs toward the cribriform plate. Therefore, the danger for the cribriform plate and the olfactory mucosa is higher when performing nasal swabs compared to performing nasopharyngeal swabs. Our measurements suggest that swabs of nasal testing kits should not be inserted for a distance longer than 3-4 cm into the nasal cavity of adults to avoid temporary reduction of olfaction. The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase mankind's overall knowledge that can then improve patient care. 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