Soft Tissue Neck X-Ray Positioning: AP & Lateral Upper Airway Views
"Soft tissue neck — rule out foreign body." Or worse: a two-year-old with stridor, sitting bolt upright, drooling, refusing to lie down. Few exams reward calm, precise positioning more than the soft tissue neck, and few are more stressful when the airway is genuinely compromised.
The soft tissue neck study (also called the upper airway series) uses the air column as natural contrast to outline the pharynx, larynx, and trachea. It is a different study from the cervical spine series — the target is the airway and its surrounding soft tissues, not the bony vertebral column — and it answers different clinical questions: epiglottitis, croup, retropharyngeal swelling, and radiopaque foreign bodies.
This guide covers the two routine projections — AP and lateral upper airway — plus the cross-table lateral for the patient who cannot sit upright, with centering points, respiration instructions, evaluation criteria, and the registry-high-yield pathology signs. SID, grid, exposure, and the exact projection set must come from the validated facility protocol and technique chart; this guide is educational, not a universal recipe.
Why the Soft Tissue Neck Study Is Different
The cervical spine series is an osseous study: it demonstrates the vertebral bodies, the odontoid, and the zygapophyseal joints to clear trauma. The soft tissue neck study is a soft-tissue study: the air-filled pharynx, larynx, and trachea provide negative contrast that outlines the epiglottis, the aryepiglottic folds, the vocal cords, and the prevertebral soft tissues.
💡 Why It Matters
Air is the contrast agent. Without it, the airway walls blend into the surrounding soft tissues and you see nothing. That is why respiration instructions are the single most important part of this exam: full inspiration distends the tracheal air column on the AP view, and quiet, gentle breathing prevents distortion of the airway on the lateral view.
Three features make the exam high-yield on the ARRT registry:
- The thumb sign — a swollen epiglottis on the lateral view, the hallmark of acute epiglottitis
- The steeple sign — subglottic narrowing on the AP view, the hallmark of croup (acute laryngotracheobronchitis)
- Prevertebral soft tissue measurement — an objective check for retropharyngeal swelling that every technologist should know
Anatomy: What the Air Column Outlines
| Structure | Level | Role in imaging |
|---|---|---|
| Nasopharynx | Above the soft palate | Proximal limit of the air column on the study |
| Hyoid bone | C3–C4 | Landmark; must not superimpose the laryngeal airway when positioned correctly |
| Epiglottis | C3–C4 | Leaf-shaped cartilage guarding the laryngeal inlet; the target of the lateral view |
| Larynx (vocal cords) | C3–C6 | Houses the vocal cords and epiglottis |
| Trachea | C6 → T5 | Air-filled tube from the larynx to the bronchi; begins at C6 |
| Retropharyngeal / prevertebral space | C2–C4 | Soft tissue between the vertebral bodies and the pharyngeal air shadow |
Clinical pearl: the hyoid bone sits at the C3–C4 level and is visible on the lateral view. If the hyoid is superimposed over the airway, the mandible is likely superimposing too — the chin was not elevated enough. Recheck the position before exposing.
AP Upper Airway Projection
The AP projection is the first view of the routine series and the view that demonstrates subglottic narrowing — the hallmark of croup.
Patient Positioning
- SID: 72 inches (180 cm) — the long SID minimizes magnification of the airway
- Patient position: Upright preferred, facing the tube; midsagittal plane (MSP) perpendicular to the IR
- Adjustments: Arms at sides; shoulders depressed; chin elevated slightly
- CR: Perpendicular to the IR at the level of C4 — midway between the laryngeal prominence (Adam's apple) and the jugular notch; top of the IR at the external auditory meatus (EAM)
- Respiration: Deep breath in and hold — full inspiration fills the airway with air; expose on full inspiration
- Shielding: Gonadal shielding where applicable (Merrill's)
📌 Exam Tip
Full inspiration is not optional on the AP view — it expands the tracheal air column, which is what lets you see the subglottic region. An AP soft tissue neck taken on expiration can look falsely narrowed.
Evaluation Criteria (AP)
- Coverage: air-filled trachea and larynx from the nasopharynx through the proximal trachea included
- Rotation check: sternoclavicular joints equidistant from the spine — no rotation
- Motion check: sharp soft-tissue and bony margins — no swallowing motion
- Technique check: air column visible through the larynx and trachea without over-penetration of the cervical spine
- Clinical aim: airway patency; identify narrowing, obstruction, or foreign body
Lateral Upper Airway Projection
The lateral projection is the most important view in suspected epiglottitis — it best demonstrates the swollen epiglottis (the "thumb sign"). It is also the view used for the prevertebral soft tissue measurement.
Patient Positioning
- SID: 72 inches
- Patient position: Upright preferred, left lateral (or right — the side facing the tube is protocol-dependent); midcoronal plane (MCP) perpendicular to the IR
- Adjustments: Shoulders depressed and pulled back; chin elevated slightly to avoid mandible superimposition
- CR: Perpendicular to the IR at the level of C4; top of the IR at the EAM
- Respiration: Quiet inspiration or slow, gentle breathing — especially if epiglottitis is suspected; expose during inspiration
- Shielding: Gonadal shielding where applicable
⚠️ Epiglottitis Caution
A patient with suspected epiglottitis must remain upright and calm — never force them supine, and never position in a way that distresses them. Epiglottitis can progress rapidly to complete airway obstruction; the technologist's job is a quick, gentle lateral view and immediate communication with the clinical team.
Evaluation Criteria (Lateral)
- Coverage: air-filled upper airway from the nasopharynx through the proximal trachea
- Rotation check: cervical vertebrae in true lateral alignment
- Motion check: clear, sharp soft-tissue outlines without blur
- Technique check: mandible and hyoid bone not obscuring the airway; tracheal air column visible
- Clinical aim: demonstrate the epiglottis, larynx, and upper trachea for airway pathology
Why upright? Upright positioning prevents airway collapse, reduces aspiration risk, and improves visualization of the air column. For maximal airway distention, the child is typically imaged with the neck extended and breath held in inspiration — together these minimize prevertebral soft tissue redundancy and maximally distend the airway.
Cross-Table Lateral (Trauma or Critical Airway)
When the patient cannot sit or stand — trauma, or a critically compromised airway — the cross-table lateral is the alternative:
- SID: 72 inches
- Patient position: Supine or seated if unable to stand; IR placed vertically beside the neck
- Adjustments: Do not move the neck if trauma is suspected; align the CR perpendicular to the IR at C4
- Respiration: Quiet breathing if possible; do not disturb the patient's airway
- Exposure: On inspiration
Evaluation criteria: coverage from nasopharynx through proximal trachea; posterior cervical spine superimposed; air column margins distinct with no swallowing or breathing blur.
Normal Prevertebral Soft Tissue Measurements
The lateral view is also where you measure the prevertebral (retropharyngeal) soft tissues — the space between the anterior vertebral bodies and the posterior airway wall. This is a classic objective check:
| Location | Normal upper limit |
|---|---|
| Nasopharyngeal space (C1) | 10 mm (adult) |
| Retropharyngeal space (C2–C4) | < 7 mm (any age) |
| Retrotracheal space (C5–C7) | < 22 mm (adult); < 14 mm (child < 15 y) |
- Measurement: from the anterior cortex of the vertebral body to the posterior airway wall, on a true lateral
- If the space between the lower anterior border of C3 and the pharyngeal air shadow is > 7 mm, suspect retropharyngeal swelling — e.g., hemorrhage, often an indirect sign of a C2 fracture in trauma
- The retrotracheal space should be less than the width of one vertebral body
- After trauma, prevertebral swelling is usually due to hematoma from an occult fracture — even with normal-appearing bone, widening should prompt further imaging
⚠️ Pseudo-Thickening Pitfall
Flexion, expiration, or crying (in children) artificially widen the prevertebral space and mimic pathology. Only measurements on a true lateral with the neck in neutral extension during inspiration are valid — a point worth knowing for the registry and for avoiding a false-positive read.
Recognizing the Pathology Signs
Thumb Sign — Epiglottitis (Lateral View)
Acute epiglottitis causes severe inflammation and marked edema of the epiglottis and aryepiglottic folds. On the lateral radiograph, the epiglottis loses its normal thin, leaf-like appearance and becomes thick and rounded — the thumb sign. Thickened aryepiglottic folds accompany it.
- Classic presentation: rapid onset stridor, drooling, tripod posture (leaning forward, chin thrust out), sore throat out of proportion to exam findings
- The patient is an airway emergency — keep upright, keep calm, and do not attempt throat examination or supine positioning
- Historically most common in children (Haemophilus influenzae type b, now largely prevented by vaccination); can occur in adults
Steeple Sign — Croup (AP View)
Croup (acute laryngotracheobronchitis) produces subglottic edema. Because the subglottis is the narrowest part of the pediatric airway, even small amounts of edema cause marked narrowing. On the AP view, the subglottic tracheal air column appears progressively narrowed and tapered — the steeple sign. Overdistension of the hypopharynx may also be seen.
- Registry discrimination: steeple = AP view (croup); thumb = lateral view (epiglottitis)
- Croup is typically viral, gradual in onset, with a barking cough; epiglottitis is bacterial, acute, and the child looks toxic
Foreign Bodies
Most swallowed foreign bodies are radiopaque (coins, batteries, pins) and visible on plain films. Two orthogonal views (AP + lateral) allow triangulation of the object's position — a coin in the esophagus vs. the trachea is a classic example. For radiolucent foreign bodies, a slight increase in mAs enhances soft tissue contrast to visualize airway shape changes. Never overlook the lateral view: an object positioned in the AP view may project over the spine and be missed without the second view.
Technique Notes
- kVp: a lower kVp than the routine cervical spine — roughly 65–70 kVp — is commonly used to enhance soft tissue contrast so the air–soft tissue interface is visible; the cervical spine should be faintly visible but not dominant
- mAs: higher mAs compensates for the lower kVp; increase slightly for radiolucent foreign bodies
- SID: 72 inches is standard to minimize magnification
- Grid: use per department protocol; at 72" SID many departments image without a grid
- Technique check: the air column is visible through the larynx and trachea without over-penetration — if the cervical spine is black and the airway is washed out, the kVp was too high
📌 Exam Tip
The single most common technical error on this exam is treating it like a cervical spine: too high a kVp, which destroys the soft tissue contrast. Think of the soft tissue neck as a low-kVp, high-contrast study.
Internal Linking — Build Your Knowledge
This soft tissue neck positioning guide is part of the complete head, spine, and thorax positioning library:
- Cervical Spine X-Ray Positioning — the osseous study of the same region; AP, lateral, Swimmer's, obliques, and flex-ext views
- Skull X-Ray Positioning — adjacent head projections, including the Towne view that shares the orbito-meatal baseline
- Chest X-Ray Positioning — the trachea continues into the thorax; the PA chest shows the tracheal air column from above
- Fluoroscopy Procedures and Safety — how dynamic airway evaluation (swallow studies) complements plain films
- X-Ray Modality Overview — general radiography technique and physics
- CT Scan Modality Overview — CT is often the definitive study for deep neck infections and complex foreign bodies
Test Your Knowledge — Educational Practice Questions
📝 Practice Questions
Question 1: Which projection and sign pair correctly describes croup on the soft tissue neck study?
Question 2: At what level is the central ray directed for the upper airway on both the AP and lateral soft tissue neck projections?
Question 3: What is the normal upper limit of the retropharyngeal space (C2–C4) on a lateral soft tissue neck radiograph?
Question 4: Why is the lateral soft tissue neck performed upright rather than recumbent whenever possible?
Question 5: A patient with suspected epiglottitis arrives in your department. Which of the following is the correct technologist action?
Quick Reference — Soft Tissue Neck Positioning Checklist
Use this checklist before every soft tissue neck X-ray exam:
- ✅ Confirm the order is soft tissue neck (upper airway), not cervical spine
- ✅ Upright position preferred — never force supine if epiglottitis is suspected
- ✅ SID 72 inches; top of IR at the EAM; CR at C4 (level of laryngeal prominence)
- ✅ AP view — shoulders depressed, chin elevated, full inspiration breath hold
- ✅ Lateral view — shoulders depressed and pulled back, chin elevated to clear the mandible, quiet inspiration (gentle breathing)
- ✅ No rotation — SC joints equidistant on AP; cervical vertebrae in true lateral
- ✅ Low kVp technique (~65–70 kVp) for soft tissue contrast; airway visible without over-penetration
- ✅ Prevertebral space check: C2–C4 < 7 mm; C6 < 22 mm adult / < 14 mm child — true lateral, inspiration only
- ✅ Two orthogonal views for foreign body triangulation
- ✅ Epiglottitis: quick lateral, calm patient, notify the team immediately
Authoritative Sources
- UMSystem Clinical Preceptor Reference Guide for Student Radiographers, "Soft Tissue Neck" chapter — AP upper airway, lateral upper airway, and cross-table lateral positioning with CR at C4, 72" SID, respiration instructions, and evaluation criteria (accessed 2026-08-07).
- Merrill's Atlas of Radiographic Positioning and Procedures, Workbook Chapter 3 (Soft Tissue Neck) — CR at the level of the laryngeal prominence for the upper airway, manubrium for larynx and superior mediastinum; slow inspiration to fill the trachea with air.
- Introduction to Radiology (University of Virginia), "Imaging of the Cervical Spine — Soft Tissue Space" — prevertebral space normal limits: nasopharyngeal (C1) 10 mm adult; retropharyngeal (C2–C4) 5–7 mm; retrotracheal (C5–C7) 14 mm child / 22 mm adult; C3 > 7 mm suggests retropharyngeal swelling (accessed 2026-08-07).
- Rojas CA, Vermess D, Bertozzi JC, et al. Normal thickness and appearance of the prevertebral soft tissues on multidetector CT. AJNR Am J Neuroradiol. 2009;30(1):136–41 — normal prevertebral thickness values and the flexion/expiration pseudo-thickening pitfall.
- Pediatric Imaging (pediatricimaging.org), "Epiglottitis" and "Croup" reference articles — thumb sign, steeple sign, and hypopharyngeal overdistension (accessed 2026-08-07).
- ARRT Examination Content Specifications — official exam scope; not a facility protocol.
Radiography 101 Clinical Team
Educational resource for radiologic technology students and professionals. This guide is for educational purposes and does not replace the imaging order, clinical assessment, or institutional protocol.