This present study displays the largest detailed investigation of etiology, microbiological spectrum, and surgical as well as anti-infective treatment strategies of PA, addressing a clinical challenge in head and neck surgery.
In terms of demographics, our study showed a similar sex distribution with a male predominance compared to prior literature [9]. However, the age distribution slightly differed, with the mean age in this study being 57.5 years compared to the 4th or 5th decade reported by Saibene et al. [9]. The results affirm that PA can arise across all age groups.
Overall, 14.1% of all patients in our study displayed impairment of the immune system. These findings align with prior research, which showed that immunocompromising conditions were a predisposing factor for parotid abscess [10–12]. Furthermore, oro-dental issues [13], autoimmune disorders [14], ductal and/or parenchymal disorders [11,12,15], superinfected adenolymphoma [16], specific disseminated diseases including melioidosis and tuberculosis [17,18], and immunodeficiency due to conditions like HIV infection or diabetes mellitus [15,17,19] have been described as predisposing factors. Interestingly, although immunosuppression seems to predispose to PA, it did not have an impact on clinical course or complication rate in the present study.
Moreover, we showed that patients with chronic parotitis, including Sjögren`s syndrome, exhibited a significantly higher risk of recurrence compared to other etiologies. Previous literature, including the review by Saibene et al., lacked detailed information on various etiologies [9]. In contrast, our study extensively investigated the etiology of parotid abscesses, offering comprehensive results that include the frequency of tumors as a contributing factor and showing that patients with a dental focus of PA had a significantly longer hospital stay than those without for the first time. The latter may be due to a lack of awareness of a dental focus as etiology of a PA despite the close anatomical relationship between the teeth of the upper jaw and the parotid gland, and consequently a delayed dental consultation. Therefore, the present data support routinely ruling out a dental focus in case of first diagnosis of PA.
Therapeutic management strategies involve both the drainage of pus and the administration of an appropriate antibiotic therapy [10,13,20–22]. Our study found abscess incision and drainage to be the most common treatment strategies, followed by aspiration either with or without radiological guidance, according to prior literature [9]. There is no study investigating differences in the type of anesthesia performed in PA. In this study a relevant number of patients underwent surgery under local anesthesia and there was no significant correlation between type of anesthesia and length of hospital stay or complication rate. Notably, neither patients treated under general, nor patients treated under local anesthesia showed postoperative impairment of the facial nerve. These results imply that both, general and local anesthesia, can be applied safely and effectively for surgical treatment of PA. Insertion of a wound drain was significantly associated with a longer hospital stay in the present study. On the other hand, patients without a drain did not show a higher rate of recurrences, more complications or a longer period of antibiotic administration compared to those with intraoperative drain insertion. However, it has to be mentioned that only 2 out of 79 surgically treated patients did not receive a drain. Therefore, the results are not sufficient to answer the question of the necessity of wound drain insertion in the surgical treatment of PA.
Furthermore, we demonstrated a mean hospital stay of 7.3 ± 4.7 days, which was shorter than previously described in literature (13.8 ± 9.1) [10]. The shorter mean hospital stay seems justifiably against the background of a low recurrence rate of only 5.2% in the present series. Nevertheless, the length of hospital stays and the length of administration of intravenous antibiotics have to be determined depending on clinical and laboratory findings in each individual case.
In literature, antibiotic therapy typically involves aminopenicillin alone or in combination with a beta-lactamase inhibitor or clindamycin combined with third or fourth generation cephalosporins for patients with a high incidence of gram-negative bacterial infections [3,9–11,13,20]. This is consistent with our findings, where most patients received an aminopenicillin alone or in combination with a beta-lactamase inhibitor as empiric antibiotic therapy. The mean antibiotic therapy duration was 9.8 days, consistent with prior literature recommending 10-14 days [4].
In our study, the most frequent postoperative complications were salivary fistulas agreeing with literature findings [9]. Our study revealed no new cases of facial nerve palsy during and after treatment, which was one major, but rare complication described in literature [3,9,10]. Furthermore, previous studies reported wound healing problems, which were not observed in our study [9]. Severe complications such as jaw osteomyelitis, temporal lobe abscess [23] craniocervical necrotizing fasciitis [24], descending mediastinitis [25], airway obstruction, septicemia, and septic shock [11,25,26] did not occur during the follow-up of our patients.
Prior microbiological profiling of PA revealed common pathogens like Staphylococcus spp., anaerobic bacteria, and Streptococcus spp. [3,10,11,27], consistent with our findings. Furthermore, Klebsiella spp., Haemophilus spp., Enterobacter spp., Prevotella spp., Parvimonas spp., Burkholderia spp., Pseudomonas spp., Mycobacterium spp., non-Mycobacterium spp., Propionibacterium spp., and Brucella spp. have also been isolated in reported cases of PA [3,5,6,11,14,15,18,20,21,28]. In addition to the previously mentioned pathogens, our study identified Aggregatibacter aphrophilus, Corynebacterium kroppenstedtii, various Candida species, a single instance of methicillin-resistant Staphylococcus aureus (MRSA), and Francisella tularensis – a zoonotic pathogen typically associated with wild animals. It is noteworthy that these pathogens have not been previously detected in cases of parotid abscess according to our knowledge. The high number of specimens containing no microorganisms is consistent with prior findings. One study found 14 of 25 cases of PA with negative bacterial cultures [4]. Prior antibiotic treatment may be the reason for the high number of specimens without detection of microorganisms. Therefore, starting systemic antibiotics after collection of the microbiological specimen may be beneficial to achieve a higher detection rate. Additionally, microbiological analysis of tissue samples instead of swabs could potentially improve the detection rate as well.
We evaluated antibiograms of the examined patients. Among cases where an antibiogram was generated, the empirically selected antibiotic agent aligned with the antibiogram results predominantly. However, in seven instances, the antibiotic therapy had to be modified following the antibiogram, which emphasizes the need of intraoperatively obtaining a microbiological specimen in order to gain precise knowledge about local species distribution and antibiotic resistances in PA. This is of special relevance since in one patient MRSA was isolated.
Moreover, the histopathologic specimen taken during surgical therapy of PA revealed a superinfected neoplasm in ten cases (five adenolymphomas, four parotid cysts, and one squamous cell carcinoma). We therefore strongly advocate considering an infected neoplasm as a differential diagnosis for PA and to routinely obtain a histological specimen in PA in order to exclude a tumorous etiology.
A limitation of this study is the retrospective study design. Additionally, factors as abscess size and the patient’s clinical condition were not considered, which could have influenced the decision of surgical technique and to opt for drainage. Moreover, we were unable to retrospectively ascertain whether antibiotic therapy had been initiated prior to microbiological examination. Further, this study exclusively contained patients with surgically treated PA. Consequently, patients with small PA which have not been captured by ultrasound imaging (i.e., in the deep parotid lobe) and have improved with medical therapy alone are not included. It therefore stays unclear if empirical medical treatment alone may be sufficient for small PA. Despite having a significantly larger case count than previous investigations, the collective size still may not adequately address rarer complications and etiologies, warranting further research in this domain. Larger multicenter studies are recommended for future research to validate and expand upon these results.
To sum up, the present study presents data on the largest described series of patients treated for PA including a comprehensive analysis of microbiological and clinical data. The study confirms that antibiotic agents and drainage are the two crucial pillars of treatment for PA being sufficient to avoid major complications. The results support the safety of surgical therapy of PA under local anesthesia. A dental examination should routinely be performed in case of PA to rule out a dental focus. Obtaining a microbiological specimen in order to modify antibiotic therapy if necessary and obtaining a histopathological specimen to rule out a tumorous etiology seems obligate.