Head and Neck Ultrasound – Comprehensive Notes (POCUS)

Head and Neck Ultrasound – Comprehensive Notes

  • Background and Scope

    • Point-of-care ultrasound (POCUS) for head and neck can rapidly identify and evaluate: bony and soft tissues of the hypopharynx and anterior neck, epiglottis, thyroid, cricothyroid membrane (CTM), tracheal cartilages, lymphatic system, and sinuses.
    • Superficial location and differing echogenicities make these structures well-suited for sonography.
    • Indications include evaluation of undifferentiated masses, painful regions, and pre-procedural planning to understand underlying anatomy.
    • POCUS as adjunct for airway assessment and intubation confirmation.
    • Airway management is critical in emergency resuscitation; POCUS increasingly used in diagnosis and management of airway-related disorders.
    • American Heart Association Adult Advanced Cardiovascular Life Support guidelines support POCUS as adjunct for evaluation of airway placement.
    • As POCUS practice evolves, more applications and techniques have expanded at the bedside.
    • This chapter reviews sonographic assessment of head/neck structures and the following pathologies: epiglottitis, angioedema, vocal cord dysfunction, sialolithiasis, parotitis, PTA (peritonsillar abscess), sinusitis, thyroid disorders, thyroid cysts, thyroglossal duct cysts, branchial cleft cysts, lymphadenitis, lymphadenopathy, and airway management.

  • Indications for POCUS in Head/Neck (key triggers)

    • Airway management
    • Dyspnea
    • Dysphagia
    • Dysphonia
    • Inability to manage secretions
    • Jaw pain/facial swelling
    • Neck pain
    • Neck mass
    • Supplementary information: Online supplement available at the DOI link provided

  • Diagnoses Covered (high-yield list)

    • Epiglottitis
    • Angioedema
    • Vocal cord dysfunction
    • Sialolithiasis
    • Parotitis
    • Peritonsillar abscess (PTA)
    • Sinusitis
    • Thyroid dysfunction (e.g., De Quervain’s, Hashimoto’s, Graves’ Disease)
    • Thyroid cysts/nodules
    • Thyroglossal duct cysts
    • Branchial cleft cysts
    • Lymphadenitis
    • Lymphadenopathy

  • Core Views and Techniques (overview)

    • Core Views are typically obtained in transverse and longitudinal planes; oblique views may be needed for non-midline esophagus/branchial cleft cysts.
    • For subglottic structures, a short-axis approach can be used with the probe in the submandibular region.
    • Superficial structures are imaged with a high-frequency linear probe; wider field-of-view can be obtained with extended field of view or a curvilinear probe.

  • Core View 1A and 1B: Epiglottis

    • Approach: Sniffing position. Place probe on anterior neck, inferior to the hyoid bone, in sagittal plane; rotate 90° to transverse between hyoid (superior) and thyroid cartilage (inferior).
    • Appearance analogy: epiglottis and strap muscles resemble a frog/sloth face.
    • Structures visualized: hyoid bone, thyroid cartilage, thyrohyoid membrane, strap muscles, epiglottis.
    • Core View 1A (Sagittal epiglottis) shows hyoid (yellow star) and epiglottis (red arrowhead).
    • Core View 1B (Transverse epiglottis) shows strap muscles (yellow stars) and epiglottis (red arrowhead).

  • Core View 2: Tongue

    • Approach: Submandibular space with curvilinear probe in sagittal orientation; rock and fan to center tongue; rotate 90° to transverse.
    • Structures visualized: lingual arteries, tongue, palate.
    • Core View 2A (Sagittal tongue): oral cavity measured in blue; tongue thickness in orange.
    • Core View 2B (Transverse tongue): oral cavity in blue; tongue thickness in orange.

  • Core View 3: Vocal cords

    • Technique: Best visualized in transverse orientation starting at thyroid cartilage and moving caudally.
    • Confirmation: have patient vocalize or hum to confirm movement.
    • Structures visualized: true vocal cords, thyroid cartilage.

  • Core View 4: Submandibular and Sublingual Glands

    • Approach: Probe under the medial mandible in sagittal orientation; fan to visualize hood-like hyperechoic gland; add color Doppler to assess hypervascularity.
    • Structures visualized: submandibular glands, sublingual glands.

  • Core View 5: Parotid Gland

    • Approach: Linear probe in preauricular space in coronal orientation; rotate 90° to transverse view.
    • Appearance: parotid gland is hyperechoic and superficial.
    • Structures visualized: parotid gland, mandible.

  • Core View 6: Maxillary Sinuses and Thyroid

    • Maxillary sinus: place linear probe anterior face over the maxilla, sagittal orientation just inferior to orbit; rotate to transverse; sinus appears as a thin, hyperechoic linear line.
    • Thyroid: begin supine with neck extended; place probe transversely just superior to suprasternal notch, slide superiorly to visualize thyroid lobes; rotate to visualize each lobe; landmarks include SCM, CA (carotid artery), JV (jugular vein), and isthmus.
    • Structures visualized: right thyroid lobe, left thyroid lobe, SCM, carotid artery, jugular vein, isthmus.

  • Core View 7: Lateral Neck Anatomy (Long/Short Axis)

    • Approach: transverse plane and then oblique to visualize lateral neck structures; visualize lymph nodes and surrounding soft tissues.
    • Structures visualized: lymph node and surrounding soft tissue structures.

  • Core View 8: Lymph Node

    • Approach: place probe over suspected node; rotate 90° to view in both planes; use color Doppler to assess for hypervascularity.
    • Structures visualized: lymph node; surrounding soft tissue structures.

  • Practical Guidance on Core Views

    • Core views are typically obtained in transverse and longitudinal planes.
    • An oblique orientation may be needed for esophagus/branchial cleft cysts.
    • For subglottic structures, a short-axis approach in the submandibular region may be used.
    • Superficial location favors a linear probe; for a wider field of view, use extended field-of-view or curvilinear probe as needed.

  • Clinical Applications: Epiglottitis

    • Epiglottitis is a time-sensitive emergency; often a clinical diagnosis with overlap with other diseases.
    • POCUS is valuable: rapid, repeatable, bedside without patient transport or repositioning.
    • Epiglottis thickness thresholds from studies:
    • One study showed upper normal epiglottic AP thickness around 3.2 mm; epiglottitis group had ≥3.6 mm at lateral margins, with significant anteroposterior diameter difference.
    • Inter-rater reliability issues: intraclass correlation ~0.57 for epiglottic thickness measurements across clinicians; preepiglottic space showed better reliability.
    • The “alphabet P sign”: sagittal view with edematous half-circle inferior to hyoid bone.

  • Angioedema

    • Angioedema can require emergent endotracheal intubation in about 10–34% of ED patients.
    • Determining immediate airway need is challenging; fiberoptic nasopharyngoscopy may not be readily available.
    • Evidence for submandibular/anterior neck ultrasound predicting airway intervention is limited.
    • Observational data suggest tongue size, oral cavity dimensions, and tongue-to-cavity ratios may help predict airway difficulty, but normal tongue thickness is variable (means reported ~3.0 to 6.4 cm).
    • Laryngeal edema can be visualized in transverse view starting at thyroid cartilage and sliding inferiorly to identify vocal cords; look for asymmetry in arytenoids and surrounding soft tissues to predict intervention needs.

  • Vocal Cord Dysfunction (VCD)

    • VCD can mimic life-threatening conditions; symptoms include stridor, increased work of breathing, and respiratory distress.
    • VCD assessment with a linear probe; commonly affects pediatric patients, females, and those with prior neck surgery/trauma.
    • Gold standard is fiberoptic nasopharyngoscopy, but POCUS offers a noninvasive bedside option.
    • Normal vocal cord function: symmetric and coordinated motion; visualize by having patient phonate (e.g., prolonged "eeeee" or "aaaah").
    • Findings suggestive of VCD: laterally displaced, shortened, or thinned vocal cord; absence of movement during phonation; or glottic closure displaced from midline.
    • Additional tips: lateral neck view with cranial-caudal orientation can improve sensitivity/specificity for movement assessment.
    • Paradoxical vocal cord movement: cords close during inspiration; some reports show high accuracy with certain maneuver tests.

  • Sialolithiasis

    • Often presents with neck/jaw pain and meals-related swelling; diagnosis is typically clinical but ultrasound adds rapid confirmation.
    • Ultrasound findings: hyperechoic stones with posterior shadowing within submandibular region; dilated ducts; gland enlargement; surrounding inflammatory changes (cobblestoning and hyperemia).
    • Sensitivity/specificity for stones ≥2 mm: ~89.9% sensitivity and ~96.6% specificity (systematic review, 2022).
    • For stones <3 mm: sensitivity ~77% and specificity ~95%; false negatives more likely with small ( <3 mm ) stones in non-dilated or dilated ducts; false positives often due to ductal stenosis with wall fibrosis.
    • POCUS can confirm sialolithiasis and guide management; stones commonly seen echogenic with twinkling artifact near gland; associated abscess or sialocele may appear as anechoic fluid collection.
    • Sialolithiasis may coexist with sialadenitis; gland enlargement and ductal dilation are common.

  • Parotitis

    • Facial swelling prompts ultrasound to assess parotid enlargement, stones, and inflammatory changes.
    • Normal parotid: homogeneous echotexture; flow pattern similar to lymph node hilum.
    • Size varies with age and body habitus; adult ranges roughly 0.7–3.7 cm in width and 4.6 cm in height.
    • Inflammation: gland enlarges, ducts dilate, tissue becomes hyperemic; described visually as a “pomegranate” sign due to vascular/tissue changes.

  • Peritonsillar Abscess (PTA)

    • Indications: sore throat with unilateral posterior oropharyngeal swelling; asymmetry and surrounding hyperemia may be present.
    • Two ultrasound approaches:
    • Intraoral technique: covered endocavitary probe inside affected tonsil; identify tonsil and any associated fluid collection; assess proximity to carotid artery with color Doppler; measure lesion; look for hyperemia around the collection but no internal color flow.
    • Transcervical technique: curvilinear probe sagittal near mandible; target tonsillar area from posterior approach; visualize PTA in two planes and assess carotid proximity with color Doppler; drainage can be performed in-plane.
    • Drainage guidance: intraoral or transcervical in-plane drainage possible.
    • Diagnostic performance (POCUS): PTA sensitivity ~74% and specificity ~79% when combining intraoral and transcervical techniques; intraoral alone ~91% sensitive and 75% specific; transcervical ~80% sensitive and 81% specific; pediatric data show similar trends.
    • POCUS can reduce length of stay and may improve drainage outcomes; post-procedure assessment of drainage adequacy is possible; case reports of post-procedural hematoma visualization exist.

  • Sinusitis

    • Often clinical; objective documentation of sinus inflammation can be via rhinoscopy, nasal endoscopy, or CT.
    • Ultrasound utility varies; sensitivity ~72.7%–96.4%; specificity ~25%–93.2% across studies.
    • Pediatric maxillary sinusitis: sensitivity ~64%, specificity ~95%.
    • Technique: place probe over the sinus with depth ≥4 cm to visualize posterior wall; assess for mucosal thickening, mobile air-fluid levels with position changes, or complete opacification with visible posterior wall.
    • Posterior wall visibility is limited unless fluid is present.

  • Thyroid Gland and Thyroid Disorders (US as main imaging modality)

    • Normal thyroid dimensions: transverse diameter ~4–6 cm; anteroposterior diameter ≤2 cm; volume ~10–15 mL.
    • Hashimoto’s thyroiditis (chronic lymphocytic thyroiditis): hypoechoic gland with micronodules and degraded margins.
    • De Quervain’s thyroiditis (subacute): enlarged, slightly hypoechoic, heterogeneous with normal or reduced vascular flow.
    • Graves’ disease: enlarged thyroid (often 2–3× normal volume); mixed echogenicity; hypervascular on color Doppler.
    • Thyroid cysts/nodules: nodules are common; ultrasound sensitive for detection but limited for ruling out malignancy; fine-needle aspiration biopsy (FNA) is used for malignancy assessment.
    • Nodule risk features (malignancy): echogenicity, calcifications, margins, and vascularity.
    • Benign lesions: isoechoic or hyperechoic, with halo, smooth margins, peripheral vascularity; cystic or spongiform characteristics.
    • Suspicious nodules: hypoechoic, irregular margins, microcalcifications, intranodular flow; examples shown as intermediate and high-suspicion nodules.
    • Thyroglossal duct cysts: fluid-filled, located between strap muscles; move with tongue protrusion or swallowing; irregular with mixed internal echogenicity.
    • Branchial cleft cysts: typically along anterior border of sternocleidomastoid; well-defined margins; uniform anechoic fluid contents.
    • Growth patterns and prevalence: thyroglossal duct cysts common congenital neck masses; branchial cleft cysts less common; both benign.

  • Thyroid and Neck Masses – Additional Context

    • Hashimoto’s and De Quervain’s thyroiditis share imaging characteristics of hypoechogenicity and heterogeneity with micronodules; Hashimoto’s is autoimmune and a common cause of hypothyroidism; De Quervain’s typically follows a viral infection.
    • Graves’ disease shows hypervascularity and diffuse enlargement; nodular goiters may be multicystic with variable vascularity.
    • Lymph nodes: the neck contains nearly half of the body's lymph nodes.
    • Normal nodes: <1 cm in adults; <2 cm in pediatric patients.
    • Benign lymphadenopathy/lymphadenitis: midrange size (~1–2 cm) with increased flow.
    • Malignancy: nodes that are immobile, matted, or >1.5 cm require further evaluation; malignant nodes are often hypoechoic, round, heterogeneous, and may show cystic necrosis.

  • Lymph Nodes – Detailed Characteristics

    • Lymphadenopathy is a general term for enlarged nodes; infection is the most common cause.
    • Ultrasound sensitivities for detecting malignancy range from ~75% to ~98%; specificities range from ~41% to ~91.5% across studies.
    • Features suggesting malignancy: hypoechoic, round shape, heterogeneity, cystic necrosis.
    • Nodes >1.5 cm that are mobile or matted require more evaluation; in patients >40 years, persistent lymphadenopathy >4 weeks, >2 cm, progressive swelling, systemic symptoms, or diffuse enlargement increases concern for malignancy.

  • Airway Management and POCUS

    • Emergent airway management is a cornerstone of acute/critical care; >10% of emergent intubations have adverse events.
    • POCUS can help predict difficult airway, guide endotracheal tube (ETT) size, confirm ETT location.
    • DOPES framework (Sono-DOPES is a POCUS-enhanced extension): Dislodgement, Obstruction, Pneumothorax, Equipment malfunction, Breath stacking.
    • Diagnostic sequence (Sono-DOPES) includes transtracheal ultrasound for ETT location/depth, bilateral lung sliding for ventilation, and monitoring diaphragmatic movement.
    • If no lung sliding with ETT in the proper location, ventilate and reassess; if unilateral sliding, consider pneumothorax; use lung pulse to differentiate single-lung issues from pneumothorax.
    • Static vs dynamic approaches for ETT confirmation:
    • Dynamic: observe flutter-like movement of ETT during intubation (snowstorm sign).
    • Static: post-intubation assessment of trachea and esophagus; ETT within trachea appears as a second thin line posterior to trachea; esophageal intubation shows a second air-mucosa interface lateral/posterior to trachea (double tract sign).
    • ETT depth assessment after initial confirmation: rotate probe to sagittal to view second tracheal ring; remove cuff air and instill 5–10 mL saline to enhance visualization; measure distance from ETT cuff to second tracheal ring.
    • If anterior margin of cuff is above second ring, ETT is too high and should be advanced.
    • If cuff is between the second and sixth rings, ETT is in the correct location.
    • If cuff is below the sixth ring or not visualized, ETT is too deep and should be withdrawn.
    • Techniques can be performed statically or dynamically depending on clinical circumstance and operator availability.

  • Sono-DOPES Algorithm (Table 17.2 recap)

    • Diagnostic assessment aligned with potential etiologies:
    • Dislodged ETT
    • Obstruction of the tube
    • Pneumothorax
    • Equipment malfunction
    • Breath stacking
    • Imaging steps:
    • Transtracheal ultrasound to assess ETT location and depth.
    • Bilateral lung sliding assessment to confirm air entry into lungs.
    • If unilateral lung sliding is present, continue evaluation; if absent, assess for pneumothorax with additional signs such as lung pulse.
    • If there is no lung sliding and ETT is in the proper location, disconnect from ventilator and reassess with manual ventilation; then re-check lung sliding and diaphragm movement.
    • The table emphasizes a systematic, ultrasound-guided approach to acute airway problems.

  • Cricothyroidotomy and CTM Identification (POCUS-guided landmarks)

    • Cricothyroidotomy is a time-sensitive procedure used when intubation is not possible.
    • POCUS improves CTM identification: up to 2× improvement in average anatomy; 5–10× improvement in poorly defined anatomy; often can be performed in under 30 seconds and with minimal training.
    • Pre-procedure planning: position the patient for cricothyroidotomy; ultrasound landmarks help identify CTM before incision.
    • Landmark anatomy for CTM identification:
    • Transverse view: place probe over thyroid cartilage; find the triangular thyroid cartilage (“taco” shape); slide caudally to the air line at the CTM with reverberation artifact deep to the CTM; move further caudally to the cuff prior to ultrasound to guide incision.
    • Longitudinal view: starting at central neck below thyroid cartilage; identify tracheal rings as bright hypoechoic rings with A-lines; identify cricoid cartilage just cranial to the trachea; identify hyperechoic cricothyroid membrane; identify thyroid cartilage above.
    • Mark the CTM on skin in the planned procedure position; or if premarking is not possible, use a saline-filled needle as a guide (Seldinger-like approach).

  • Pearls and Pitfalls (practical tips)

    • Superficial head/neck anatomy makes high-frequency linear probes ideal; apply appropriate pressure to optimize image quality without compressing delicate structures.
    • Epiglottis is not routinely visible in the long axis in healthy individuals.
    • Incidental findings during scanning of thyroid, lymph nodes, etc., are common; inform patients and arrange follow-up imaging as indicated.
    • If intraoral PTA assessment is limited by trismus, an extraoral submandibular approach with a lower-frequency probe can be used.
    • Ultrasound can assess ETT location/depth and ventilator-related complications.
    • Various approaches to endotracheal assessment (dynamic vs static) are valid; tailor approaches to clinical context and resource availability.
    • For anticipated difficult airways requiring intubation, ultrasound can help identify the CTM as part of pre-procedural planning and may guide needle/scalpel in real time.

  • Key Ultrasound Findings (summary table insights)

    • Epiglottitis: thickened epiglottis; alphabet P sign; edema around inferior epiglottis.
    • Angioedema: tongue/laryngeal edema; variable tongue thickness; potential airway compromise.
    • Vocal cord dysfunction: abnormal cord movement patterns; paralyzed or misdirected movement; asymmetric cords.
    • Sialolithiasis: hyperechoic stones with posterior shadowing; dilated ducts; gland enlargement; twinkling artifact.
    • Parotitis: enlarged gland with ductal dilation and hyperemia; parotid vascular changes (pomegranate sign).
    • PTA: abscess fluid collection with surrounding hyperemia; color Doppler to assess proximity to carotid vessels; two approaches described (intraoral and transcervical).
    • Sinusitis: mucosal thickening, mobile air-fluid levels, posterior wall opacification; posterior wall visibility may require fluid presence.
    • Thyroid disorders: varied echogenicity; Hashimoto’s shows micronodules with hypoechogenicity and margin degradation; De Quervain’s shows enlarged, heterogeneous, hypoechoic gland with reduced flow; Graves’ shows diffuse enlargement with hypervascularity.
    • Thyroid nodules: benign patterns (isoechoic/hyperechoic, halo, smooth margins, peripheral vascularity); suspicious features (hypoechoic, irregular margins, microcalcifications, intranodular flow, extrathyroid extension, taller-than-wide geometry).
    • Thyroglossal duct cysts: fluid-filled, midline or suprahyoid location, tongue movement-related mobility; irregular contents.
    • Branchial cleft cysts: lateral neck location along anterior SCM; well-defined margins; uniform anechoic content.
    • Lymph nodes: size thresholds, shape, margins, vascularity; malignancy signs (hypoechoic, round, heterogeneous, cystic necrosis).
    • ETT assessment and depth: tracheal/tracheal ring visualization; cuff depth relative to second/6th rings; dynamic vs static assessments; snowstorm and double tract signs for intubation events.
    • CTM identification: TACA technique for quick and robust landmarking.

  • Numerical and Statistical Highlights (selected values in context)

    • Epiglottitis thickness thresholds and reliability:
    • Upper normal ap thickness: ~3.2 ext{ mm}; epiglottitis threshold at lateral margins: ~3.6 ext{ mm}.
    • Inter-rater reliability for epiglottic thickness: intraclass correlation ~0.57.
    • Epiglottitis sign:
    • Alphabet P sign visualized as edematous inferior half-circle to hyoid shadow on sagittal view.
    • Angioedema
    • Proportion requiring emergent intubation: 10 ext{–}34 ext{ extpercent} of patients.
    • Tongue and airway predictors (for difficult airway)
    • DSE (distance from skin to epiglottis): threshold > 2.54 ext{ cm}; sensitivity Se = 0.82; specificity Sp = 0.91.
    • DSVC (distance from skin to vocal cords): Se = 0.75; Sp = 0.75.
    • Hyomental distance (HMD): HMD < 4.0 ext{ cm} predicts difficult airway.
    • HMD extension/neutral ratio: threshold rac{HMD{extension}}{HMD{neutral}} = 1.2 with reported high sensitivity (close to 100%) and specificity around 90.5%.
    • Tongue thickness: greater than 6.1 ext{ cm} increases risk of difficult intubation; reported sensitivity ≈ 71 ext{ extpercent}; specificity ≈ 75 ext{ extpercent}.
    • PTA diagnostic performance (POCUS)
    • Combined intraoral and transcervical: ext{Sensitivity}
      oughly 74 ext{ extpercent}; ext{Specificity}
      oughly 79 ext{ extpercent}.
    • Intraoral alone: Se ext{ ~} 91 ext{ extpercent}, Sp ext{ ~} 75 ext{ extpercent}.
    • Transcervical alone: Se ext{ ~} 80 ext{ extpercent}, Sp ext{ ~} 81 ext{ extpercent}.
    • Sinusitis ultrasound performance varies; pediatric maxillary sinusitis: sensitivity ext{S} ext{~} 64 ext{ extpercent}, Sp ext{~} 95 ext{ extpercent}. Overall sinusitis ultrasound sensitivity 72.7%–96.4%; specificity 25%–93.2% across studies.
    • Thyroid imaging benchmarks: normal thyroid dimensions and nodularity prevalence (nodule present in ~one-third of general population);
    • Nodule risk stratification features: taller-than-wide, irregular margins, microcalcifications, extrathyroidal extension, vascular patterns.
    • ETT depth depth-criteria: ETT cuff distance to second tracheal ring used to assess placement; ideal cuff-to-ring distance corresponds to cuff between 2nd and 6th rings (inclusive).

  • Important Figures and Descriptions (textual references)

    • Epiglottis and frog/sloth-face appearance in sagittal and transverse planes.
    • Vocal cords visualization with motion during phonation; normal symmetric vibration; examples of abnormal cord movement in VCD.
    • Sialolithiasis images show hyperechoic stones with shadowing; thymus of glands with twinkling artifacts.
    • PTA views with intraoral and transcervical approaches showing fluid collection margins, carotid proximity, and drainage guidance.
    • Parotid gland ultrasound appearances including pomegranate sign in inflamed parotid.
    • Thyroglossal duct cysts and branchial cleft cysts imaging characteristics and typical locations.
    • Lymph node ultrasound findings including malignant features: roundness, hypoechogenicity, heterogeneity, cystic necrosis.

  • Practical Takeaways for Exam Preparation

    • POCUS provides rapid, bedside assessment of head/neck anatomy and common pathologies, with a focus on airway adjuvancy, diagnostic accuracy, and procedural guidance.
    • Understand the key core views and what pathologies they help assess (epiglottis, tongue, vocal cords, salivary glands, thyroid, lymph nodes).
    • Memorize characteristic ultrasound findings for each pathology and the relative advantages of intraoral vs transcervical PTA approaches.
    • Be familiar with airway ultrasound metrics (DSE, DSVC, HMD, HMD ratio, tongue thickness) and their clinical thresholds for predicting difficult intubation.
    • Know the ETT confirmation and depth assessment techniques, including dynamic (snowstorm) and static signs, and how to measure cuff depth to second tracheal ring.
    • Recognize CTM landmarks and the TACA rule to identify cricothyroid membrane quickly in urgent airway situations.
    • Review the Sono-DOPES framework for systematic airway troubleshooting with ultrasound.

  • References and Further Reading

    • Foundational text and chapter authors: Bales, Boulger, Boyd; Advanced Point-of-Care Ultrasound, Springer Nature Switzerland AG, 2025.
    • Selected references cited in the chapter include guidelines and ultrasound-focused airway management studies (e.g., bed-side diagnosis of acute epiglottitis, airway management ultrasound studies, PTA ultrasound techniques).

  • Quick Summary of Key Formulas and Thresholds (for quick recall)

    • Epiglottitis thickness threshold (lateral margins): ext{epiglottic thickness} o ext{epiglottitis with } ext{upper margin} ext{around } 3.6 ext{ mm}
    • DSE threshold for difficult airway: DSE > 2.54 ext{ cm}, ext{Se }=0.82, ext{Sp }=0.91
    • DSVC: Se = 0.75, Sp = 0.75
    • Hyomental distance (HMD): HMD < 4.0 ext{ cm} o ext{difficult airway predicted}
    • HMD extension / neutral ratio: rac{HMD{extension}}{HMD{neutral}} = 1.2 (high sensitivity and specificity reported)
    • Tongue thickness for difficult intubation: ext{tongue thickness} > 6.1 ext{ cm}
    • PTA diagnostic performance: ext{Se} ext{ ~} 0.74, ext{Sp} ext{ ~} 0.79 ext{ (combined intraoral + transcervical)}
    • Sinusitis ultrasound performance ranges: S ext{ ~} 0.727 ext{–}0.964, Sp ext{ ~} 0.25 ext{–}0.932
    • Thyroid nodule risk features include: taller-than-wide geometry, irregular margins, microcalcifications, extrathyroid extension, irregular vascularity.