Correct Answer: A. Carotid body tumor
Lyre's sign (or Lyon's sign) is the pathognomonic clinical finding in carotid body tumor—lateral and medial displacement of the carotid artery bifurcation on angiography or ultrasound, creating a characteristic "lyre" or "splayed" appearance. The carotid body is a chemoreceptor organ located at the carotid bifurcation, derived from neural crest cells (paraganglioma). These tumors present as a slowly growing, painless, pulsatile mass at the angle of the mandible (the anatomical site of the carotid bifurcation). On clinical examination, the mass is mobile laterally but restricted vertically (Fontaine's sign). The diagnosis is confirmed by imaging—ultrasound shows splaying of the carotid bifurcation; CT/MRI demonstrates a hypervascular mass; angiography reveals the characteristic "lyre" sign. Most carotid body tumors are benign (95%), though 5% are malignant. Indian surgical practice follows Bailey & Love guidelines for management: small asymptomatic tumors may be observed; symptomatic or enlarging tumors require surgical excision with careful dissection to preserve carotid vessels and cranial nerves (IX, X, XII). The key discriminator is the combination of location (carotid bifurcation), slow growth, painlessness, and the pathognomonic Lyre's sign on imaging.
Why the other options are wrong
B. Thyroid nodule — Thyroid nodules arise from the thyroid gland itself, located lower in the neck (below the larynx). They do not produce Lyre's sign because they do not involve the carotid bifurcation. Thyroid masses move with swallowing and are typically firm, not pulsatile. The angle of the mandible is above the thyroid, making this anatomically incorrect. C. Lymphadenopathy — Lymph nodes are non-pulsatile, firm, and often multiple. They do not produce the characteristic splaying of the carotid bifurcation (Lyre's sign). Lymphadenopathy at the angle of the mandible is usually tender, especially if reactive or infected, whereas carotid body tumors are painless. Imaging would show discrete nodes, not vascular displacement. D. Branchial cyst — Branchial cysts are remnants of the branchial apparatus, typically located anterior to the sternocleidomastoid muscle (anterior triangle), not at the carotid bifurcation. They are fluid-filled, non-pulsatile, and do not cause vascular splaying. Imaging shows a cystic lesion without internal vascularity, not the hypervascular mass with Lyre's sign characteristic of carotid body tumor.
High-Yield Facts
- Lyre's sign = lateral and medial splaying of carotid bifurcation on imaging (pathognomonic for carotid body tumor).
- Fontaine's sign = lateral mobility but vertical restriction of the mass (distinguishes carotid body tumor from other neck masses).
- Carotid body tumor location = angle of mandible at the carotid bifurcation; derived from neural crest (paraganglioma, not true neoplasm).
- 95% of carotid body tumors are benign; malignancy risk increases with size >5 cm and rapid growth.
- Imaging modality of choice = ultrasound (shows splaying) or CT/MRI for surgical planning; angiography reserved for preoperative assessment.
- Surgical risk = cranial nerve injury (IX, X, XII) and carotid artery injury; careful dissection required per Bailey & Love guidelines.
Mnemonics
LYRE = Lateral and medial splaying + carotid bifurcation L = Lateral displacement, Y = bifurcation (Y-shaped), R = carotid artery, E = at angle of mandible. Remembers the pathognomonic sign and location together. CBT = Carotid Body Tumor (slow, painless, pulsatile, at angle) Slow growth + painless + pulsatile + angle of mandible = think carotid body tumor first. Use when you see 'slowly growing neck mass at angle of mandible.'
NBE Trap
NBE may pair "slowly growing neck mass" with thyroid nodule (common neck pathology) to trap students who don't recall the specific anatomical location (angle of mandible = carotid bifurcation, not thyroid). The Lyre's sign clue is the discriminator that separates this from routine thyroid pathology.
Clinical Pearl
In Indian surgical practice, carotid body tumors are often discovered incidentally on ultrasound screening for neck masses. The key bedside finding—pulsatility and lateral mobility—combined with imaging confirmation of Lyre's sign allows confident diagnosis without biopsy (which risks hemorrhage). Most patients tolerate observation if asymptomatic; surgery is reserved for symptomatic or enlarging tumors, with careful preoperative angiography to assess collateral circulation before carotid sacrifice.
_Reference: Bailey & Love's Short Practice of Surgery, Ch. 40 (Neck); Harrison's Principles of Internal Medicine, Ch. 397 (Neuroendocrine tumors)_