Pneumocephalus as result of nonsurgical peri‐implantitis treatment with an air‐polishing device for submucosal debridement—A case report

Abstract Background A subcutaneous emphysema is an infrequent but potentially life‐threatening complication after dental treatment involving instruments functioning with pressurized air. Emphysemata after the use of high‐speed handpieces and air‐syringes are well documented, however, more recently several reports on emphysemata produced by air‐polishing devices during management of peri‐implant biological complications have appeared. To the best of our knowledge, direct development of pneumocephalus after a dental procedure has never been reported before. Introduction of air likely contaminated with oral bacteria to the intracranial space bares the risk of developing meningitis. Case Presentation This case report describes the spreading of a subcutaneous emphysema into the intracranial space (i.e., development of a pneumocephalus) after treatment of a peri‐implantitis lesion with an air‐polishing device equipped with the nozzle for submucosal debridement. A subcutaneous emphysema was noticed during the use of an air‐polishing device and the subsequent computed tomography (CT) examination revealed a quite unexpected spreading of the emphysema into the intracranial space. The patient was admitted to the hospital for close surveillance, CT follow‐up, and intravenous antibiotics to prevent the development of meningitis due to the introduction of air—likely contaminated with oral bacteria—into the intracranial space. After 3 days, the patient was discharged in good condition without any further complications. Conclusion In case of an extensive subcutaneous emphysema as result of a dental procedure, a more extended radiographic examination including the mediastinal and cranial space should be considered, to assess the risk for potentially life‐threatening complications.


| INTRODUCTION
A subcutaneous emphysema is an infrequent but potentially lifethreatening complication after dental treatment. The first case report describing such a complication was published in 1900 (Turnbull, 1900), and regarded a patient who played a bugle soon after tooth extraction and developed an enormous swelling of the face on the side of extraction. Reviews (Busuladzic et al., 2020;Heyman & Babayof, 1995;McKenzie & Rosenberg, 2009) have summarized published cases of subcutaneous emphysemata in relation to dental treatment, summing up to about 150 cases within the last 60 years (i.e., from 1960 to 2018); most of the reported emphysemata were caused by air-driven handpieces and air syringes.
However, as air-polishing devices are frequently used in the management of peri-implant biological complications (Klinge et al., 2018), it is not surprising that emphysemata have also been reported after their use (Alonso et al., 2017;Bassetti et al., 2014; La Monaca et al., 2021;Lee et al., 2018).
Emphysemata can usually spread into the facial, (peri-)orbital, pharyngeal, cervical, and/or mediastinal regions. Rarely, air can be introduced into the circulatory system causing systemic air embolism, as observed in a case of a subcutaneous emphysema spreading to the mediastinum, that caused cerebral hypoperfusion (Magni et al., 2008).
In most cases, the emphysema resorbs spontaneously within a few days and complete recovery is achieved after 7-10 days, while a surgical intervention is only seldomly required in cases with (suspected) infection and/or incomplete resolution (Busuladzic et al., 2020;Cardo et al., 1972;Lee et al., 2018;McKenzie, & Rosenberg, 2009).
Potentially life-threatening complications are infections due to the introduction of oral bacteria into the fascial spaces (e.g., necrotizing fasciitis, or mediastinitis) and/or the resulting mechanical compression of surrounding tissues/organs due to the associated internal swelling (e.g., pneumopericardium, tracheal compression) (McKenzie & Rosenberg, 2009;Mascarenhas, 2019). Therefore, in most cases antibiotics are prescribed together with analgesic medication for pain control; the additional prescription of steroids and/or 100% O 2 supplementation may also be considered. In severe cases, patients are admitted to the hospital for close surveillance and administration of intravenous antibiotics (Busuladzic et al., 2020;Heyman & Babayof, 1995;McKenzie & Rosenberg, 2009;Lee et al., 2018).
The present case report is-to the best of our knowledge-the first to report on the direct introduction of air into the intracranial space (i.e., pneumocephalus) after a dental procedure, specifically, after submucosal debridement of a peri-implantitis lesion with an airpolishing device.

| CASE REPORT
The present case report follows the CARE guidelines (Riley et al., 2017) (Supporting Information: Appendix S1) and the patient has provided a signed informed consent on publishing the case including clinical pictures and radiographs.

| DISCUSSION
Since 1960, about 150 case reports have been published on the development of a subcutaneous emphysema in relation to a dental procedure (Busuladzic et al., 2020;Heyman & Babayof, 1995; McKenzie & Rosenberg, 2009). These reports described emphysemata in quite diverse locations, spreading from the orbital region to the mediastinum. In the present case, we observed introduction of air into the intracranial space; to the best of our knowledge, direct development of pneumocephalus resulting from a dental procedure has not been reported before.
According to a review (Markham, 1967), summarizing 295 cases with pneumocephalus, the cause for intracranial air accumulation is most often trauma leading to fractures of the skull and especially of the facial skeleton, for example after automobile or motorcycle accidents. Pneumocephalus is also frequently related to neurosurgical F I G U R E 3 The pterygoid canal (a) and the forum rotundum (b) could be considered as potential entry points for the air into the intracranial space; especially within the canal leading to the foramen rotundum several smaller air bubbles were captured on the CT scan (b). CT, computed tomography.
F I G U R E 4 3D reconstruction (a-h) of the emphysema (red) and display of the potential pathways to the intracranial space, i.e., along the inferior orbital fissure and finally via the foramen rotundum (green) and/or via the pterygoid canal (yellow). 3D, three-dimensional.
interventions, neoplasm, and infections involving the skull (Markham, 1967;Schirmer et al., 2010). Rarely, pneumocephalus may also develop in the absence of any fracture and/or visible lacerations on the skin or conjunctiva after compressed-air injury to the eye (Akbari- Kamrani et al., 2020;Bagheri et al., 2018;Hiraoka et al., 2013;Koenig, 1977;Lubniewski & Feibel, 1989;Williams & Frankel, 1999;Yuksel et al., 2007). It is assumed, that compressed air may enter the retrobulbar space via some invisible disruption and micro-lacerations of the conjunctiva or that it may even be able to pass through intact conjunctival tissue (Hiraoka et al., 2013), and that the air enters then the intracranial space via the optic canal (Williams & Frankel, 1999;Yuksel et al., 2007) and/or superior orbital fissure (Lubniewski & Feibel, 1989).
In the present case, where a pneumocephalus developed during submucosal debridement of a peri-implantitis lesion with an airpolishing device, the following pathway for the intracranial entrance of the air is suspected based on the localization of air, registered in the diagnostic CT taken after the procedure. Based on this CT scan, and although it is acknowledged that the detection of a thin buccal bone wall in CT/CBCT scans is largely inaccurate (Domic et al., 2021), it appears that the implant in position 27 had an intact buccal bone at its marginal aspect (Figure 6a). However, it had a very deep periimplant bone defect at its mesial aspect, extending almost to the apex of the implant, that is, into the augmented sinus space (Figure 6b,c).
Additionally, there was a bone defect at the buccal aspect of the sinus wall-most likely a remnant of the lateral window made during the sinus floor elevation procedure-at a similar level as the bottom of the intrabony defect (Figure 7). Hence, as the nozzle was inserted at the mesial aspect of the implant, the compressed air could have A patient diagnosed with pneumocephalus should be immediately admitted to a hospital. Keeping the patient as an inpatient allows close surveillance, including bed rest, and the possibility for appropriate treatment. This can include intravenous administration of antibiotics to prevent the development of meningitis and of antipyretic pain medication to prevent hyperthermia, supplementation with 100% O 2 for a faster resorption rate, and/or serial CT scans to monitor gradual resorption of the intracranial air (Gorissen et al., 2019;Schirmer et al., 2010). It should be noted that antibiotic prophylaxis in case of pneumocephalus to prevent meningitis is controversially discussed, for example, antibiotic prophylaxis is not supported by the literature for patients with basilar skull fractures (Nellis et al., 2014;Ratilal et al., 2015). Nevertheless, the likely introduction of oral bacteria into the intracranial space was regarded as additional risk factor for meningitis, and therefore the current patient received intravenous antibiotics at the admitting hospital.
F I G U R E 5 A CT scan on the next day indicated resolution of the intracranial air and regression of the subcutaneous emphysema. The section plane and level in a-h correspond to the section plane and level presented in a-h of Figure 2. CT, computed tomography.
In previous publications reporting on emphysemata by means of an air-polishing device, during the nonsurgical treatment of periimplantitis, the lack of a buccal bone wall and/or keratinized buccal mucosa have been discussed as potential risk factors for their development (Alonso et al., 2017;Bassetti et al., 2014;Lee et al., 2018), but this was not the case for the current patient (Figures 1 and 6a). Another relevant parameter seems to be the airpressure exiting from the various tips, of the various handpieces, at various power settings, but there is only limited information available on this parameter among the various devices in the market. For example, according to the manufacturer of the device used in this report, the exiting pressure from the disposable nozzle of the subgingival handpiece-within a periodontal/peri-implant pocketcan reach maximum 1.8 bar. Further, treatment time may potentially affect the risk of emphysema development. It seems reasonable to assume that with longer treatment time, close to the bottom of the defect, and at a given power setting, the risk for emphysema development may be higher as larger amounts of pressurized air would be delivered and the tissues might become less resilient.
However, shorter treatment time might result in a less clean implant surface compared to longer treatment time . In perspective, the maximum pressure and/or time of treatment below which no emphysema may occur is currently unknown and probably impossible to estimate. It seems reasonable that the likelihood to develop a subcutaneous emphysema depends on the interplay among local anatomical conditions (e.g., defect extent, tissue consistency), hardware specifications (e.g., exiting pressure, tip-design), and the way of using the device (e.g., appropriate setting adjustment to the specific site, duration of use). Considering the facts that the number of implants placed is increasing and that peri-implant biological complications are frequent, as well as that air-polishing devices are often used in their management (Klinge et al., 2018), it is reasonable to expect that emphysemata may become more frequent. Thus, further research is needed to provide evidence-based recommendations for the safe use of air-polishing devices in the management of peri-implantitis.

| CONCLUSION
The present case of direct development of pneumocephalus from a dental procedure is the first in the literature, and thus it should be regarded as an extremely rare complication. However, it is suggested that in case of an extensive subcutaneous emphysema, a more F I G U R E 6 The implant in position 27 presented with a sufficient buccal bone wall (a), but the peri-implant bone defect (b) extended at the mesial aspect far apically (c) potentially in connection via the augmentation material with the residual bone defect in the lateral sinus wall presented in Figure 7.