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...

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...

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