Retrospective Observational Study of Computed Tomography-Based Vascular Risk Assessment During Needle Drainage of Peritonsillar Abscess

Summary

The purpose of this protocol is to measure the distances of peritonsillar abscesses from the Internal Carotid Artery (ICA), External Carotid Artery, and Internal Jugular Vein using contrast-enhanced Computed Tomography, to detect ICA course anomalies, and to assess the risk of vascular injury during drainage quantitatively.

Abstract

Peritonsillar abscess (PTA) is a common deep neck infection in which bedside drainage is performed close to major cervical vessels. Although catastrophic vascular complications are rare, clinicians have limited quantitative information on how far the internal carotid artery (ICA), external carotid artery (ECA), and internal jugular vein (IJV) lie from the abscess in individual patients. This protocol describes a contrast-enhanced computed tomography (CT)-based workflow to confirm unilateral PTA, acquire neck CT images under standard clinical settings, measure linear distances from the anterior and posterior abscess capsule to the ipsilateral ICA, ECA, and IJV, compare these distances with the contralateral healthy side as an internal control, and classify the theoretical risk of ICA injury during needle drainage using a modified Pfeiffer system. The procedure includes patient selection, safety screening for iodinated contrast, contrast-enhanced CT acquisition, standardized axial image review by a head and neck radiologist, and structured data recording and analysis. In a retrospective cohort of 94 adult patients, PTA consistently displaced the ICA, ECA, and IJV away from the tonsillar space, increasing both anterior and posterior distances compared with the healthy side. The mean posterior PTA-ICA distance was approximately 14 mm, whereas the contralateral tonsil-ICA distance was about 9 mm. ICA course anomalies (tortuosity or coiling) were detected in a minority of patients, and roughly one in seven cases met moderate-risk criteria because of shorter distances and/or aberrant ICA anatomy. Age, sex, and abscess volume did not significantly alter these relationships. This CT-based protocol provides a reproducible method to quantify PTA-vessel distances and identify patients with potentially higher vascular risk anatomy prior to drainage. It supports cautious, controlled-depth needle aspiration in most cases and highlights scenarios in which image-guided or operating-room drainage may be preferable.

Introduction

Peritonsillar abscess (PTA) is a collection of pus between the palatine tonsillar capsule and the superior pharyngeal constrictor muscle, most often arising as a complication of acute tonsillitis. It is the most common deep neck infection and a frequent otolaryngologic emergency, particularly in young adults, with an incidence of approximately 18-30 cases per 100,000 population and a peak in the 20-40-year age group¹. Patients typically present with severe unilateral sore throat, fever, hot-potato voice, trismus, dysphagia, and pooling of saliva. Prompt recognition and drainage, together with appropriate antibiotics, are essential to prevent airway compromise and spread of infection to deeper neck spaces, which may lead to mediastinitis, jugular vein thrombosis, sepsis, and other life-threatening complications^2,3. Because the palatine tonsil is in proximity to the internal carotid artery (ICA), external carotid artery (ECA), and internal jugular vein (IJV), drainage of PTA carries a theoretical risk of major vascular injury. The ICA, which courses posterolateral to the tonsillar fossa, is generally regarded as the structure most at risk, whereas the ECA and IJV are usually more lateral. Imaging and anatomical series have described retropharyngeal or medially displaced ICAs, in which the artery can lie only a few mm behind the pharyngeal wall, making routine pharyngeal procedures potentially hazardous^4,5,6. Case reports of carotid pseudoaneurysm or massive haemorrhage after PTA or its drainage, particularly in atypical or paediatric cases, underline that these complications, although rare, can be catastrophic^5,6.

Imaging-guided techniques have therefore attracted increasing interest. Ultrasound-guided needle aspiration allows real-time visualization of the abscess and adjacent carotid artery, potentially reducing the risk of iatrogenic vascular injury^7,8. Randomized and systematic data indicate that needle aspiration and incision and drainage (I&D) yield similar primary clinical outcomes, with very low overall complication rates; aspiration may be associated with slightly higher recurrence, but is often favored as the initial, less invasive approach^9,10,11.

Despite these concerns, quantitative data on how PTA alters the spatial relationship between the tonsillar region and major neck vessels remain limited. In a CT-based study, Taslı et al.¹² reported that PTA increased the mean posterior PTA-ICA distance to 13.39 ± 3.7 mm compared with approximately 9.6 mm on the contralateral side and found an aberrant ICA course in 17.6% of patients. Unlike the study by Taslı et al., which primarily evaluated posterior PTA-ICA distance and the frequency of ICA anomalies, the present protocol systematically measures both anterior and posterior distances to the ICA, ECA, and IJV on the abscess and contralateral sides. It combines this data with a clinical risk classification (Pfeiffer's system) to generate a CT-based framework for procedural risk assessment.

Major hemorrhagic complications and carotid pseudoaneurysm after PTA drainage are exceptionally rare. Published data are limited to isolated case reports and small series, and even in the largest available systematic review, only a handful of carotid lesions were identified over several decades of studies¹³. As a result, the true prevalence of persistent post-procedural bleeding and carotid pseudoaneurysm cannot be expressed as a reliable percentage. However, these events clearly occur at the case-report level rather than as a common outcome of routine drainage. Nevertheless, their potential severity justifies attempts to optimize drainage techniques and improve procedural safety.

However, detailed measurements for multiple vascular structures and systematic risk stratification based on ICA course in adults with PTA are still scarce. The present CT-based study, therefore, aimed to measure distances between PTA and the ipsilateral ICA, ECA, and IJV relative to the contralateral healthy side, document ICA course anomalies associated with PTA, and classify the theoretical risk of ICA injury during needle drainage using the clinical scheme proposed by Pfeiffer et al.^12,14. Quantitative knowledge of these distances is directly relevant for planning needle trajectory, determining safe penetration depth, and deciding whether imaging-guided or operating-room drainage is warranted in anatomically high-risk patients. However, existing work has largely focused on the ICA alone. It has not systematically quantified distances to all major cervical vessels or integrated these measurements into a practical, CT-based risk stratification scheme for needle drainage in adults with PTA¹⁵.

We hypothesized that PTA would systematically increase the distance between the tonsillar region and adjacent major vessels; however, a subset of patients would exhibit shorter distances and aberrant ICA courses, consistent with a higher theoretical procedural risk.

Protocol

This protocol was applied in a retrospective observational cohort of patients with unilateral peritonsillar abscess (PTA) who underwent contrast-enhanced neck CT as part of their standard diagnostic work-up. The Dicle University Ethics Committee approved this retrospective observational study, which was carried out at a tertiary care facility (Approval number: 06/05/2021, 310). Every procedure followed the Declaration of Helsinki. Given the retrospective nature of the analysis, all participants provided written informed consent at the time of treatment for the use of their data in research.

Study design and patient selection

Identification of eligible patients was done using the following criteria: Clinical diagnosis of unilateral PTA based on otorhinolaryngological examination (peritonsillar swelling, uvular deviation, trismus, hot-potato voice, unilateral sore throat); age ≥ 13 years; availability of a contrast-enhanced neck CT scan performed at presentation. Patients were excluded if they had a history of severe neck trauma, head and neck tumors, tonsillectomy, recent head/neck surgery, or radiotherapy, and/or congenital or acquired conditions that markedly distort cervical anatomy (e.g., large vascular malformations, major skeletal deformities).

Contrast-enhanced CT

Contrast-enhanced CT in PTA patients was done when at least one of the following applied: Inadequate intraoral examination (marked trismus, severe gagging, uncooperative patient) or uncertain diagnosis; suspicion of deep neck space extension, airway compromise, or other complications; failure of initial bedside aspiration or drainage; recurrent, bilateral, or atypical PTA; suspicion of vascular or neoplastic pathology (sentinel bleeding, pulsatile or unusually firm mass, cranial nerve deficits).

For prospective application of this protocol, obtain informed consent in accordance with local regulations and screen for contraindications to iodinated contrast and CT (contrast allergy, renal impairment, pregnancy, where applicable). Contrast-enhanced computed tomography was performed with patients in the supine position, and their heads were maintained in neutral alignment. An 18-20 G intravenous cannula was inserted into an antecubital or forearm vein suitable for power injection, and venous patency was confirmed with saline. All scans were acquired using a multidetector CT scanner with a standard neck imaging protocol. Imaging parameters included a tube voltage of 120 kVp, tube current of approximately 210 mAs or institutional equivalent, slice thickness of 3 mm, pitch of approximately 1.0 with a rotation time of 1 s, and a field of view of approximately 350 mm using a soft-tissue reconstruction kernel. The scan range extended from the skull base to the thoracic inlet. Following intravenous administration of 70-100 mL of non-ionic iodinated contrast at a rate of approximately 2-2.5 mL/s and a subsequent 20-30 mL saline flush, image acquisition was performed with a delay of 40-65 seconds to optimize visualization of cervical soft tissues and vascular structures. Patients were monitored clinically during and immediately after contrast administration, and all examinations adhered to institutional radiation safety standards in accordance with the ALARA principle. Diagnostic-quality contrast-enhanced datasets were obtained in all cases, clearly demonstrating the peritonsillar abscess, palatine tonsils, and bilateral internal carotid artery, external carotid artery, and internal jugular vein.

CT data analysis

All CT datasets were transferred to a picture archiving and communication system with multiplanar reconstruction capability and reviewed using standard soft-tissue window settings, with a window width of approximately 350-400 Hounsfield units and a window level of approximately 40 Hounsfield units. Peritonsillar abscesses were identified as low-attenuation, rim-enhancing collections adjacent to the palatine tonsil, and the affected side was recorded. Abscess dimensions were measured in the anteroposterior, transverse, and craniocaudal planes on orthogonal images, and approximate abscess volume was calculated using the ellipsoid formula when applicable.

On axial images at the level of the abscess, the ipsilateral internal carotid artery, external carotid artery, and internal jugular vein were identified as contrast-enhanced vascular structures located posterolateral to the pharyngeal wall. On the contralateral side, the palatine tonsil and the corresponding vascular structures were identified and used as internal anatomical controls. On the abscess side, the anterior surface was defined as the outer margin of the abscess capsule facing the oral cavity, whereas the posterior surface was defined as the margin facing the pharyngeal wall. On the contralateral side, the anterior and posterior contours of the palatine tonsil at the corresponding axial level served as reference surfaces.

Linear distances were measured from both the anterior and posterior surfaces of the abscess to the nearest point of the internal carotid artery, external carotid artery, and internal jugular vein. Identical measurements were obtained on the contralateral healthy side using the tonsillar contours as reference. Measurements were performed on axial images where the relevant surface and vessel were best visualized, and multiplanar reconstructions were used when necessary to ensure that the minimum distance was recorded. All distances were recorded in mm.

Determining the course of action

The course of the internal carotid artery was evaluated bilaterally at the oropharyngeal level and classified as normal, tortuous, or coiled. Vascular risk on the abscess side was determined using an adapted Pfeiffer classification. Cases with a normal lateral internal carotid artery course and a posterior abscess-to-internal carotid artery distance of 10 mm or greater were categorized as low risk, whereas cases with an aberrant internal carotid artery course and/or a posterior distance of less than 10 mm were categorized as moderate risk. No patient fulfilled the criteria for the high-risk category, which would require severe medial displacement of the internal carotid artery into the pharyngeal space.

For each patient, demographic and clinical variables, including age, sex, and side of the abscess, were recorded. Imaging-derived variables included abscess dimensions and volume when applicable, Friedman tonsil grade on the affected side, all six vessel-to-abscess distance measurements on both sides, internal carotid artery course classification, and vascular risk category. All data were entered into IBM SPSS Statistics version 21.0 or equivalent software. Continuous variables were summarized as mean values with standard deviations and minimum-maximum ranges, and categorical variables were summarized as counts and percentages. Comparisons between the abscess and the contralateral sides were performed using paired Student's t-tests or appropriate non-parametric equivalents. Associations between vascular distances and age or abscess volume were assessed using Pearson or Spearman correlation analyses. The prevalence of aberrant internal carotid artery anatomy and the distribution of vascular risk categories were also reported.

Results

Following these steps yields a reproducible, CT-based protocol for quantifying PTA-vessel distances, detecting ICA course anomalies, and classifying the theoretical risk of vascular injury during needle drainage in patients with peritonsillar abscess.

In routine clinical practice, contrast-enhanced CT is reserved for patients in whom the diagnosis is uncertain or the intraoral examination is limited (e.g., marked trismus, severe gag reflex, or uncooperative patient), deep neck space extension, airway compromise, or other complications are suspected, initial aspiration or drainage fails or yields no pus, the abscess is recurrent or clinically atypical, or vascular, neoplastic, or other unusual pathology is suspected (e.g., sentinel bleeding, a pulsatile or unusually firm mass, or cranial nerve deficits).

A senior radiologist with expertise in head and neck anatomy examines each CT scan on a workstation. Since the same senior radiologist performed all distance measurements, inter-observer reliability was not assessed. Axial images were measured in a standard way for every patient (Figure 1). We measured the minimum distance between each vascular structure (ICA, ECA, and IJV) and the tonsillar region's anterior surface. We also measured the minimum distance between the tonsillar region's posterior surface and each structure. Both the PTA side-the side with the abscess-and the contralateral side, which has the healthy tonsil, were used for these measurements.

The anterior edge of the abscess cavity, facing the oral cavity, was referred to as the anterior surface of the abscess side. In contrast, the posterior edge, facing the pharyngeal wall, was referred to as the posterior surface. The vessels on the healthy side were measured using the tonsil's anterior and posterior bounds, which are analogous points. For each of these six measurement points (anterior-ICA, anterior-ECA, anterior-IJV, posterior-ICA, posterior-ECA, and posterior-IJV), the distances to the internal carotid artery (ICA), external carotid artery (ECA), and internal jugular vein (IJV) were noted. Multiplanar reformation was used to ensure the smallest distance was recorded in cases where the vessel could not be visualized on that slice. Furthermore, we evaluated each side's ICA course by observing any aberration, which is characterized as a coiled or tortuous path that brings the artery closer to the pharynx or medially than usual. In particular, we observed whether the ICA showed coiling (creating a loop or siphon shape) or tortuosity (significant curvature or bending) in the segment next to the oropharynx. The method used to obtain these measurements on CT images is shown in Figure 2.

Clinical characteristics and patient demographics

The study included 94 patients with unilateral peritonsillar abscesses (41 females and 53 males). The mean age of the patients was 30.5 ± 10.7 years, with a range of 13 to 65 years. Table 1 summarizes important clinical and sociodemographic features. Out of all patients, 42 cases (44.7%) of the abscesses were on the left side, while 52 cases (55.3%) were on the right. According to CT measurements, the average abscess volume was 8.1 ± 2.9 cm³, with a range of 2.6 to 14.5 cm³. Patients arrived at the hospital on average 5.3 ± 1.5 days after the onset of symptoms (range 3-9 days). According to Friedman's scale, the majority of patients had significantly enlarged tonsils on the affected side: 37 patients (39.5%) had Grade 2 tonsils, and 57 patients (60.6%) had Grade 3 tonsils¹⁶. The majority of patients (80 patients, or 85.1%) fell into the low-risk category, according to Pfeiffer's risk classification for ICA injury. However, due to their carotid anatomy, 14 patients (14.9%) were categorized as being at moderate risk. The severe medial carotid displacement associated with a high-risk category was not present in any of the patients. Significant vascular variations were present in a few of the moderate-risk patients. Out of all patients, 9 patients (9.6%) had an aberrant ICA course, while 85 patients (90.4%) had no discernible aberration of the carotid artery on the abscess side. In all 9 patients, the contralateral ICA followed a normal course; no bilateral aberration was observed. Three (3.1%) of those 9 aberrant cases were caused by coiling, and 6 (6.3% of the total) were caused by tortuosity of the ICA. These 9 patients had a median age of 28.3 ± 8.5 years (range 18-52); 3 were female, and 6 were male. Out of the 9 cases, 6 aberrant ICAs were on the right and 3 on the left side. These results suggest that although vascular abnormalities are uncommon, a tiny but significant portion of PTA patients do have carotid anatomy that may increase their risk of harm.

According to the data above, the gender distribution of the patient population was about equal, and PTAs were marginally more prevalent on the right side. Although roughly 1 in 7 patients had an anatomical variant that raised concerns, the majority of patients were categorized as low risk for vascular injury, and the majority of abscesses were moderate in size.

Vascular-abscess distances (Healthy side vs. Abscess side)

By comparing the abscess side to the normal side, the study's main conclusions concern the distances between the peritonsillar region and the nearby major blood vessels. A statistical comparison of these distances is shown in Table 2. Compared to the normal anatomy on the opposite side, we discovered that the presence of a PTA in every case resulted in a greater distance between the tonsillar tissue (or abscess capsule) and the vessels. This is held for all three vascular structures (ICA, ECA, and IJV) as well as for the anterior and posterior measurements. With p < 0.05 for every comparison, these differences were statistically significant.

The mean distance on the anterior side between the abscess and the ICA (A-ICA) was 31.2 ± 5.3 mm, while on the healthy side it was 22.7 ± 5.8 mm. Stated differently, the ICA was, on average, ~8.5 mm farther away at the front edge of the abscess than it would be at the same location on a normal tonsil. The other vessels showed a similar pattern: the anterior distance to the IJV (A-IJV) was 36.7 ± 4.6 mm vs. 31.4 ± 4.3 mm normal, and the anterior distance to the ECA (A-ECA) was 26.3 ± 4.6 mm with PTA vs. 21.1 ± 2.5 mm normal. The statistical significance of all these anterior differences was high (p < 0.001).

The abscess provided some increase, but the distances were naturally smaller on the posterior side, where it is closest to the carotid sheath and the pharyngeal wall. On average, there was a 5 mm increase in the mean distance between the posterior abscess wall and the ICA (P-ICA) from 14.1 ± 3.5 mm to 9.1 ± 1.7 mm on the healthy side. The posterior distance to IJV (P-IJV) was 18.6 ± 4.2 mm compared to 15.2 ± 3.3 mm normal, and the posterior distance to ECA (P-ECA) was 10.3 ± 2.9 mm with PTA vs. 7.4 ± 1.3 mm standard. Once more, every one of these posterior differences was significant (p < 0.001). These findings support the notion that, in comparison to an unaffected tonsil, a peritonsillar abscess tends to push the carotid artery and other vessels outward (laterally or posteriorly), increasing the cushion of space between the abscess and the vessels. The mass effect of the abscess and inflammatory swelling is probably the cause of this phenomenon.

Interestingly, the absolute values still show that the carotid artery can stay relatively close to the abscess in some patients, even with these increases in mean distances. For example, although the mean distance here was 14.1 mm, the minimum observed distance from PTA to ICA posteriorly was only 7 mm. This emphasizes the need for caution because some patients had little space between the ICA and the abscess wall. The previously mentioned risk classification considered both distance and any abnormal ICA routing; 14 patients were classified as moderately risk, primarily due to their carotid arteries being tortuous or closer than usual (some of these had distances on the lower end of the observed range).

In conclusion, Table 2 shows that the abscess side had greater measured distances to the three main vascular structures than the normal side. This suggests that the abscess typically pushes the external carotid, jugular vein, and carotid artery outward due to its mass effect. The posterior-to-ECA distance (~10 mm with PTA) had the smallest absolute gap, whereas the anterior-to-IJV distance (averaging ~37 mm with PTA) had the largest. The healthy side distances show how close these vessels normally lie to the tonsillar capsule under normal circumstances, especially posteriorly (for example, on a healthy side, the ICA can be, on average, only ~9 mm from the posterior tonsillar wall). The consistent increase in distance caused by the abscess across the patient sample is confirmed by the highly significant p-values.

Gender differences

Next, we looked at whether the patient's gender impacted the abscess-to-vessel distances. The distances on the PTA side, broken down by gender (41 females vs. 53 males), are summarized in Table 3. The mean distances in the male and female subgroups were comparable, and statistical analysis revealed that none of the six distance measurements differed significantly between the sexes (all p > 0.05). For example, the average A-ICA distance for female patients was 30.7 ± 4.7 mm, while the average for male patients was 31.6 ± 5.6 mm (p > 0.05). P-ICA was also 14.5 ± 3.7 mm for females and 13.7 ± 3.4 mm for males (p > 0.05). These small variations lacked statistical significance. Additionally, no gender effect was observed for either IJV or ECA distances. This implies that the proximity of the abscess to these vessels was not substantially impacted by differences in male and female anatomy (such as body size or neck circumference) within the sample. The outward displacement of vessels caused by the abscess was similar in both men and women.

Age and Abscess Volume Correlation

The potential effect of patient age on abscess-to-vessel distances was also evaluated, based on the hypothesis that older patients might exhibit increased vascular tortuosity or atherosclerotic changes that could alter anatomical relationships. Correlation analysis demonstrated that age was not significantly associated with any of the measured distances, including anterior and posterior distances to the internal carotid artery, external carotid artery, and internal jugular vein. Pearson correlation coefficients were uniformly low, and no statistically significant correlations were observed (all p values > 0.1). Within the age range of the cohort (13-65 years), patient age therefore had no discernible impact on the spatial relationship between the peritonsillar abscess and adjacent cervical vessels, suggesting that individual anatomical variation and abscess-related mass effect were more influential than age-related vascular changes.

In addition, the relationship between abscess volume and vessel displacement was examined. Correlation analyses using Pearson or Spearman tests, as appropriate, revealed no significant association between abscess volume and any of the measured abscess-to-vessel distances. Larger abscess volumes were not associated with either increased or decreased separation from the internal carotid artery, external carotid artery, or internal jugular vein. These findings indicate that abscess size alone did not predict the degree of vascular displacement in this cohort.

In conclusion, this study's findings suggest that a peritonsillar abscess may lessen the immediate risk of vascular damage during drainage by pushing the ICA, ECA, and IJV farther apart than is customary. Nonetheless, 15% of patients had vascular anatomy that might still be moderately dangerous, particularly the ICA course. Age and gender did not significantly alter these distances, suggesting that each patient's anatomy should be evaluated individually (instead of assuming, for instance, that older patients have a higher risk due to closer vessels). These results support our hypothesis that PTA generally displaces the major cervical vessels away from the tonsillar fossa while identifying a minority of patients with persistent high-risk anatomy.

Data availability:

De-identified measurement data (vessel distances, demographic variables, and risk classifications) supporting the findings of this study will be made available in tabular format in the Supplementary Table 1 and Supplementary Table 2 and can also be obtained from the corresponding author upon reasonable request, in accordance with institutional and national data protection regulations. Due to ethical and legal restrictions, the original CT image data cannot be shared publicly, but can be re-analyzed on site under appropriate data-sharing agreements.

Figure 1: CT-based distance measurements between the peritonsillar region and cervical vessels. Representative axial contrast-enhanced neck CT image demonstrating how linear distances were measured from the anterior and posterior surfaces of the peritonsillar abscess (PTA) capsule to the nearest point of the internal carotid artery (ICA), external carotid artery (ECA), and internal jugular vein (IJV) on the affected side; analogous measurements were obtained on the contralateral healthy side using the palatine tonsil contours as reference. Distances were recorded in mm using the PACS caliper tool. Scale bar: 10 mm. Please click here to view a larger version of this figure.

Figure 2: Identification of the ICA course and CT-based risk categorization. Representative contrast-enhanced neck CT images illustrating assessment of the ICA course at the oropharyngeal level (normal vs tortuous vs coiled) and the application of the adapted risk scheme used in this study. Cases were categorized as low risk when the ICA course was lateral/normal, and the posterior PTA-ICA distance was ≥10 mm, and as moderate risk when an aberrant ICA course was present and/or the posterior PTA-ICA distance was <10 mm. Scale bar: 10 mm. Please click here to view a larger version of this figure.

Characteristic	Value
Number of patients	94 (100%)
Age (years)	30.5 ± 10.7 (13–65)
Gender – Male	53 (56.4%)
Gender – Female	41 (43.6%)
Time from symptom onset to admission (days)	5.3 ± 1.5 (3–9)
Side of abscess – Right	52 (55.3%)
Side of abscess – Left	42 (44.7%)
Abscess volume (cm³)	8.1 ± 2.9 (2.6–14.5)
Tonsil size – Grade 2	37 (39.4%)
Tonsil size – Grade 3	57 (60.6%)
Risk classification – Low risk	80 (85.1%)
Risk classification – Moderate risk	14 (14.9%)
ICA course – No aberration	85 (90.4%)
ICA course – Aberration (any)	9 (9.6%)
– Tortuosity of ICA	6 (6.3%)
– Coiling of ICA	3 (3.1%)

Table 1: Clinical characteristics and demographics. Baseline demographics and clinical features of the cohort (N=94), including age, sex, abscess laterality, abscess volume, time to presentation, Friedman tonsil grade, ICA course classification, and adapted vascular risk category. Continuous variables are shown as mean ± standard deviation (SD) with range; categorical variables are shown as n (%). Abbreviations: ICA = internal carotid artery; cm³ = cubic centimeters.

Distance Measure	PTA Side (mm)	Healthy Side (mm)	p-value
A-ICA	31.2 ± 5.3 (20–45)	22.7 ± 5.8 (9–38)	<0.001
P-ICA	14.1 ± 3.5 (7–29)	9.1 ± 1.7 (5–13)	<0.001
A-ECA	26.3 ± 4.6 (20–35)	21.1 ± 2.5 (15–25)	<0.001
P-ECA	10.3 ± 2.9 (6–15)	7.4 ± 1.3 (5–9)	<0.001
A-IJV	36.7 ± 4.6 (27–47)	31.4 ± 4.3 (20–46)	<0.001
P-IJV	18.6 ± 4.2 (11–27)	15.2 ± 3.3 (10–22)	<0.001

Table 2: Vessel distances on the healthy side vs the PTA side. Comparison of anterior and posterior distances from the peritonsillar region to the ICA, ECA, and IJV on the PTA side versus the contralateral healthy side. All measurements are reported in mm (mean ± SD). p-values reflect paired comparisons between sides. Abbreviations: PTA = peritonsillar abscess; ICA = internal carotid artery; ECA = external carotid artery; IJV = internal jugular vein; A = anterior surface; P = posterior surface. Distances are in millimeters (mm).

Distance Measure	Female (n=41)	Male (n=53)	p-value
A-ICA	30.7 ± 4.7 (21–45)	31.6 ± 5.6 (20–42)	0.61 (NS)
P-ICA	14.5 ± 3.7 (8–29)	13.7 ± 3.4 (7–21)	0.45 (NS)
A-ECA	25.9 ± 4.6 (20–35)	26.8 ± 4.6 (20–35)	0.40 (NS)
P-ECA	10.1 ± 2.8 (6–15)	10.6 ± 2.9 (6–17)	0.55 (NS)
A-IJV	35.7 ± 4.4 (27–46)	37.4 ± 4.7 (28–47)	0.08 (NS)
P-IJV	18.3 ± 4.4 (11–27)	18.8 ± 4.1 (10–29)	0.68 (NS)

Table 3: PTA-side vessel distances by sex. PTA-side anterior and posterior vessel distances stratified by sex. Values are reported in mm (mean ± SD), and group comparisons are reported with the corresponding p-values. Abbreviations: ICA = internal carotid artery; ECA = external carotid artery; IJV = internal jugular vein; NS = not significant. Distances are in millimeters (mm).

Supplementary Table 1: Correlation between age and abscess-to-vessel distances. Pearson correlation analysis between age and each abscess-to-vessel distance measurement (A-ICA, P-ICA, A-ECA, P-ECA, A-IJV, P-IJV). Correlation coefficients (r) and p values are reported. Abbreviations: A = anterior; P = posterior; ICA = internal carotid artery; ECA = external carotid artery; IJV = internal jugular vein. Please click here to download of this file.

Supplementary Table 2: Correlation between abscess volume and abscess-to-vessel distances. Correlation analysis (Pearson or Spearman, as appropriate) between abscess volume and each abscess-to-vessel distance measurement (A-ICA, P-ICA, A-ECA, P-ECA, A-IJV, P-IJV). Correlation coefficients (r/ρ) and p values are reported. Pearson or Spearman correlation was applied as appropriate based on data distribution. Please click here to download of this file.

Discussion

Although clinically significant vascular injury during PTA drainage is exceedingly rare, the possibility of ICA puncture remains a major concern among clinicians^15,17. The findings here provide quantitative evidence that PTA generally increases the distance between the tonsillar region and the surrounding vascular structures, particularly the ICA, thereby creating an additional tissue buffer during drainage. The mean posterior PTA-ICA distance was 14.1 ± 3.5 mm vs. 9.1 ± 1.7 mm on the contralateral healthy side, closely mirroring the CT-based measurements of Taslı et al. (13.39 vs 9.6 mm)¹⁵. These concordant data suggest that abscess formation and associated inflammatory swelling tend to displace the carotid sheath laterally or posteriorly, rather than drawing the ICA closer to the drainage field. Beyond reinforcing the clinical safety of standard PTA drainage, the data refine quantitative understanding of tonsillar fossa-vessel relationships in the inflamed adult neck and provide reference values that complement cadaveric and non-PTA imaging studies.

Beyond Taslı's study, few investigations have directly quantified these relationships in PTA. However, large CT and MRI series in non-PTA populations demonstrate that a subset of patients have ICA-pharyngeal wall distances below 10 mm at the oropharyngeal level, emphasizing considerable anatomical variability^18,19.

In the present cohort, the minimum posterior PTA-ICA distance was 7 mm despite the overall lateralizing effect of the abscess, confirming that some individuals retain only a narrow safety margin. Pediatric MRI data further show that the tonsillar fossa-ICA distance in children may be only 10-15 mm²⁰. Taken together, these findings indicate that most patients have a comfortable separation between the tonsil and carotid artery, but a small minority have intrinsically high-risk anatomy that persists even in the presence of an abscess.

To better characterize this risk, we applied the clinical classification of aberrant ICA described by Pfeiffer et al.²¹. None of the patients met the criteria for the highest-risk category, in which the ICA virtually abuts the tonsillar fossa; however, 14.9% were classified as moderate-risk due to shortened distances and/or tortuous or coiled ICA courses. These variations occurred in a relatively young cohort (mean age ~30 years), suggesting that developmental or congenital factors, rather than degenerative vascular changes, may predominate. Although we observed no vascular injuries, recognition of such variants on pre-procedural imaging should prompt heightened caution and consideration of modified drainage strategies, such as controlled-depth needle aspiration or image-guided procedures.

During the study period, the institutional practice was to perform needle aspiration as the first-line drainage technique in all 94 PTA cases, with incision and drainage (I&D) reserved for cases of incomplete decompression or recurrent collections. None of the patients required immediate abscess tonsillectomy, which aligns with the view that quinsy tonsillectomy should be reserved for selected refractory or high-risk cases¹³. The present quantitative data support this pragmatic approach: even for moderately sized abscesses, the posterior PTA-ICA distance was usually ≥10 mm, and we did not encounter carotid or other major vascular injuries.

Needle aspiration is attractive because it is simple, can often be performed under local anesthesia, and, according to a Cochrane review, has a very low complication rate, with efficacy comparable to I&D⁹. Concerns about inadvertent carotid puncture during aspiration are largely theoretical and are not supported by either the presented measurements or clinical series in other studies in which no ICA injuries were detected^6,22. Based on this CT data, we propose a simple CT-informed modification of the conventional needle drainage technique. First, in patients with limited mouth opening, previous pharyngeal surgery, marked lateral pharyngeal swelling, or suspected deep neck infection, we recommend contrast-enhanced CT or ultrasound before blind drainage to define a safe needle corridor. Second, during bedside aspiration, the needle should be advanced predominantly in the sagittal plane from the superior pole of the tonsil, avoiding a posterolateral trajectory toward the carotid sheath. Third, a controlled needle depth of approximately 10-15 mm from the mucosal surface, achieved by using a needle stop or leaving only 1-1.5 cm of needle exposed, keeps the tip within the abscess cavity in almost all patients, according to published anatomic data¹⁵. Finally, when CT reveals very short posterior distances or a retropharyngeal course of the ICA, drainage should be performed with ultrasound guidance or in the operating room under general anesthesia, and bedside blind puncture should be avoided. Safety can be further enhanced by limiting needle penetration (e.g., ≤2.5 cm), using guarded needles, and, where available, incorporating real-time ultrasound guidance to visualize the abscess and carotid artery¹⁰.

In line with the general experience documented in the literature that such events are extremely rare and largely confined to individual case reports, we did not observe any vascular injury in any of the cases. In the systematic review by Klug et al., only a small number of hemorrhagic events and carotid complications were identified over several decades of PTA reports, and the authors concluded that a precise prevalence could not be calculated. However, the absolute risk appears very low in modern practice¹⁷.

For patients with unfavorable vascular anatomy on imaging-such as short PTA-ICA distances, a retropharyngeal or looping ICA, or suspicion of pseudoaneurysm-a more cautious strategy is warranted. In these settings, options include ultrasound-guided aspiration, drainage in the operating room with vascular control readily available, or, in rare instances, planned abscess tonsillectomy in collaboration with vascular surgery or interventional radiology teams^13,16,22. Such approaches are seldom required in routine adult PTA but may be lifesaving in exceptional cases.

Overall, the findings, together with recent emergency-department data from Jufara et al.²³ suggest that when standard techniques are appropriately applied, PTA drainage is very safe with respect to major vascular injury. Nonetheless, clinicians should remain aware of the small but real risk associated with anatomical variants. We recommend using imaging when the anatomy is unclear, when drainage attempts fail, or when atypical features are present; employing controlled-depth or ultrasound-guided needle aspiration in higher-risk cases; and being prepared to terminate the procedure and seek urgent surgical or interventional support if unexpected bleeding occurs. In the great majority of patients, prompt drainage combined with appropriate antibiotics leads to rapid symptom relief and excellent outcomes, with very low rates of serious complications or recurrence^14,24. Therefore, we advise clinicians who treat PTA to remain cautious: when bedside examination does not allow the operator to clearly identify the location and extent of the collection or its relationship to the tonsillar pillars and suspected vascular structures-for example in patients with severe trismus, prior tonsillar surgery, very bulky lateral or inferior pharyngeal swelling, or suspected deep-space extension-cross-sectional imaging (contrast-enhanced CT) or ultrasound should be obtained before attempting drainage; similarly, if an initial drainage attempt fails, imaging is recommended, and an ultrasound-guided approach or a needle with controlled depth should be considered, with readiness to stop the procedure and obtain prompt surgical consultation if unusual bleeding occurs.

This study, to our knowledge, is the first to operationalize a CT-based protocol that simultaneously quantifies anterior and posterior distances from the PTA to the ICA, ECA, and IJV bilaterally, and integrates these measurements with a clinical ICA risk classification to generate a practical pre-procedural risk assessment framework.

Future research

Several lines of research could further develop and validate this CT-based approach. Prospective, imaging-guided studies are needed to correlate CT-derived risk categories with actual procedural outcomes, including bleeding events and drainage success. Larger, multicenter cohorts help confirm distance thresholds and refine risk stratification across different populations and practice settings. Complementary MRI- or ultrasound-based studies, particularly in younger patients or those with contraindications to iodinated contrast, could validate and extend the distance measurements obtained on CT. Finally, dedicated investigations in pediatric and bilateral PTA cohorts are warranted to clarify age- and laterality-dependent variations in PTA-vascular relationships and their implications for drainage strategy. Future work could employ high-resolution MRI, 3D CT angiography, or intraoperative ultrasound to capture dynamic vessel movement and three-dimensional trajectories, complementing the static axial CT measurements used here.

Beyond immediate clinical decision-making, the CT-based measurements and images generated by this protocol may support head and neck anatomy teaching, surgical simulation and planning (e.g., virtual PTA drainage), radiology training modules, and computational risk modelling of vascular injury during pharyngeal procedures.

Limitations

It is crucial to acknowledge certain limitations of the method that may impact on how safety is interpreted. The patient was at rest when we took the measurements on CT scans, so actual distances and positions may vary slightly during live procedures because of patient positioning or movements (e.g., during respiration or if the patient is struggling). The angle or trajectory to reach an abscess is also important, even though we measured distances (a carotid might be safely 1 cm behind, but if one's instrument is angled incorrectly, even that distance could be traversed). We did not evaluate carotid deviation angles, which have been examined by others using 3D imaging⁷. Third, because this study was retrospective and only included patients who had CT scans, there may have been some bias introduced (perhaps CT was performed in more difficult cases or those with atypical features). However, CT provided us with a consistent method of measurement because it was available for all included patients. Since a single reader performed the measurements, inter-observer reliability could not be assessed. The single-observer design prevented inter-reader heterogeneity but did not allow for the formal assessment of inter-observer variability. Lastly, pediatric anatomy may differ (children's carotids may be more elastic and easily displaced, but their spaces are smaller), and the findings may not apply to children or to those with uncommon bilateral abscess cases (we had none bilateral at presentation). These findings could be expanded upon by larger cohort studies or prospective imaging before and after drainage.

Conclusions

Vascular injuries in PTA drainage are uncommon but not impossible, and specific anatomical factors may increase the risk. Emergency physicians and otolaryngologists should be aware that the carotid artery may lie relatively close or take an unusual path in approximately 1 out of 7 patients, necessitating careful attention²⁵. Imaging methods, such as point-of-care ultrasound or contrast CT (which we used), can be very helpful in determining the relationship between the abscess and vessels in advance. The majority of patients can safely have the abscess removed using standard procedures, such as needle aspiration or a small incision. To reduce potential risks, it is wise for people with higher-risk anatomy to think about ultrasound guidance or even to have a tonsillectomy under controlled circumstances²⁶.

The results confirm that, with regard to major vascular structures, the great majority of PTA drainage procedures can be carried out safely. Adherence to appropriate technique and meticulous pre-procedural evaluation are crucial. Clinicians can further reduce the already low risk of vascular injury by accounting for anatomical variations (like carotid tortuosity or medialization) and using the technology that is currently available for guidance. Vascular complications are extremely rare, as evidenced by the fact that none happened in this cohort. Rare instances of serious vascular complications have been reported, though, serving as a reminder to never settle for less. Critical vessels will be protected during abscess drainage with careful attention to detail, solid anatomical knowledge, and customized planning for PTA patients.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
18–20 G Intravenous Cannula	BD (Becton, Dickinson and Company)	Varies by size
Contrast Injector System	Medrad (Bayer Healthcare)	Stellant CT
Digital Caliper Tool (PACS)	GE Healthcare	AW Server
Head and Neck CT Workstation	GE Healthcare	AW Server
Iodinated Contrast Agent (Nonionic)	Bayer Healthcare	Ultravist 300
Multidetector CT Scanner (64-slice)	GE Healthcare	Revolution EVO
PACS Software	GE Healthcare	Centricity PACS
Saline Flush (0.9% NaCl)	Baxter	FKE1323
SPSS Statistics Software	IBM	Version 21.0