Musculus cricoarytenoideus dorsalis
The cricoarytenoideus dorsalis is the most important intrinsic muscle of the larynx. It originates on the dorsal surface of the cricoid cartilage and inserts on the muscular process of the arytenoid cartilage. It is the sole abductor of the arytenoid cartilage and vocal fold, opening the rima glottidis so the horse can inhale large volumes of air during exercise. All other intrinsic laryngeal muscles (except cricothyroideus) are innervated by the recurrent laryngeal nerve (a branch of the vagus, CN X); the CAD is therefore the muscle whose denervation produces the clinical syndrome of roaring. Recurrent laryngeal neuropathy almost always causes left-sided laryngeal dysfunction; the longer left recurrent nerve may contribute to this pattern. The result is progressive atrophy of the left CAD, failure of the left arytenoid to abduct fully, and an inspiratory noise plus exercise intolerance.
Origin: Dorsal surface of the cricoid cartilage
Insertion: Muscular process of the arytenoid cartilage
Action: Abducts (opens) the arytenoid cartilage and vocal fold; opens the rima glottidis for airflow during exercise
Innervation: Caudal laryngeal nerve (recurrent laryngeal nerve branch of CN X, vagus)
Diagnosis is by endoscopy (resting and/or dynamic overground/treadmill). Treatment options include prosthetic laryngoplasty (“tie-back”), ventriculocordectomy, or, in selected cases, nerve-muscle pedicle grafts or other reinnervation techniques. Ultrasound can assess CAD echogenicity.
## Overview After laryngoplasty (tie-back) surgery, the arytenoid cartilage is permanently held open to improve airflow. Because the larynx can no longer close fully during swallowing, there is a lif
Recurrent laryngeal neuropathy (RLN), commonly known as roaring or whistling, is a progressive degeneration of the recurrent laryngeal nerves, mainly affecting the left side and reducing or preventing
A whistling or roaring noise during canter or gallop, especially in a large horse, should be investigated with endoscopy. Do not continue hard training until the airway has been evaluated; performance and safety can be compromised.
## Overview After laryngoplasty (tie-back) surgery, the arytenoid cartilage is permanently held open to improve airflow. Because the larynx can no longer close fully during swallowing, there is a lifelong risk of aspiration. Coughing when eating or drinking is common. Feeding management (no grain in hay nets, feed from the ground) reduces risk. ## Causes The surgical abduction prevents complete laryngeal closure during swallowing. ## Diagnosis History of tie-back surgery and clinical signs of coughing or aspiration. ## Treatment Management changes to reduce aspiration. Treat pneumonia if it occurs. Revision surgery is occasionally needed. ## Recovery and Prognosis Exercise tolerance usually improves, but aspiration risk is permanent and requires lifelong management. ## Prevention Careful feeding practices after surgery. Signs include: coughing when eating or drinking; occasional aspiration pneumonia; improved exercise tolerance; lifelong feeding management needed
Recurrent laryngeal neuropathy (RLN), commonly known as roaring or whistling, is a progressive degeneration of the recurrent laryngeal nerves, mainly affecting the left side and reducing or preventing movement of the left arytenoid cartilage. This results in reduced airway diameter during inspiration and the characteristic inspiratory noise during exercise. It is one of the most important upper airway conditions affecting performance horses. ## What it is The left recurrent laryngeal nerve has a very long course (wrapping around the aortic arch), making it more susceptible to damage than the right nerve. Progressive axonopathy leads to denervation and atrophy of the cricoarytenoideus dorsalis (CAD) muscle, the only abductor of the arytenoid cartilage. As a result, the left arytenoid fails to open fully during exercise, causing turbulent airflow and the classic roaring sound. Laryngeal function is graded I to IV on resting endoscopic examination (Havemeyer system), with higher grades indicating greater impairment of arytenoid movement. ## Signs and symptoms - Inspiratory noise ('roaring' or 'whistling') during exercise that worsens with speed and fatigue - Exercise intolerance or reduced performance - In severe cases, respiratory distress during intense work - Abnormal arytenoid movement on resting or exercising endoscopy - The noise is often absent or minimal at rest and becomes obvious only during exercise ## Causes and risk factors RLN is a distal axonopathy whose exact cause is not fully understood but has a genetic component. It is more common in larger horses (especially Thoroughbreds and drafts) and appears to have a hereditary predisposition. Risk increases with age and size. Clinical disease is predominantly left-sided; the longer left nerve is thought to contribute. ## How it is diagnosed Diagnosis is confirmed by endoscopic examination of the larynx, ideally during exercise (dynamic endoscopy) to assess arytenoid function under stress. Resting endoscopy can grade the degree of paralysis but may underestimate the severity. The Havemeyer grading system (I to IV) is used to classify the severity based on arytenoid movement and position. ## Treatment and management Treatment depends on the grade and the horse's intended use. Horses with Grade I to II laryngeal function may not require intervention. For performance horses with Grade III or IV, surgical options include laryngoplasty (tie-back procedure), in which the arytenoid is permanently fixed in an open position, often combined with ventriculocordectomy (removal of the vocal cord and ventricle). Other procedures such as arytenoidectomy are used in selected cases. Post-operative care and rehabilitation are important for success. ## When to call the vet Contact your veterinarian if your horse develops an abnormal respiratory noise during exercise or shows signs of reduced performance. Dynamic endoscopy is the best way to confirm the diagnosis and determine the appropriate treatment. ## Prevention There is no proven way to prevent RLN, but selective breeding away from affected lines may help reduce incidence over time. Endoscopic assessment of laryngeal function can help guide decisions about whether intervention is needed. ## Frequently asked questions **Can a horse with roaring still compete?** Many horses return to successful competition after laryngoplasty (tie-back), though some degree of noise may remain and results vary. **Is roaring painful?** No. RLN itself is not painful, but the reduced airway can limit performance and, in severe cases, cause respiratory distress. **Does the tie-back surgery last forever?** The surgery provides long-term improvement in most horses, but complications such as implant failure or aspiration can occur in some cases. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Inspiratory noise ('roaring' or 'whistling') during exercise that worsens with speed and fatigue; exercise intolerance or reduced performance; in severe cases, respiratory distress during intense work; abnormal arytenoid movement on resting or exercising endoscopy; noise often absent at rest and becomes obvious only during exercise
Diagnosis is by endoscopy (resting and/or dynamic overground/treadmill). Treatment options include prosthetic laryngoplasty (“tie-back”), ventriculocordectomy, or, in selected cases, nerve-muscle pedicle grafts or other reinnervation techniques. Ultrasound can assess CAD echogenicity.
A whistling or roaring noise during canter or gallop, especially in a large horse, should be investigated with endoscopy. Do not continue hard training until the airway has been evaluated; performance and safety can be compromised.
See the Cricoarytenoideus Dorsalis (CAD) on our interactive 3D horse model. Open 3D Model