Avellis syndrome

Overview

Avellis Syndrome is a rare neurological condition resulting from a lesion in the lateral part of the medulla oblongata—part of the brainstem. It is a type of brainstem syndrome characterized by a unique combination of cranial nerve and spinal cord findings. Specifically, Avellis syndrome presents with a paralysis of the soft palate and vocal cords on the same side (ipsilateral) and a loss of pain and temperature sensation on the opposite side (contralateral) of the body.

This condition is typically caused by a vascular event such as a stroke involving the posterior inferior cerebellar artery (PICA) or vertebral artery. Due to its medullary location, Avellis Syndrome shares overlapping features with other lateral medullary syndromes, such as Wallenberg syndrome.

Causes

Avellis Syndrome arises from damage to specific structures in the lateral medulla, including the nucleus ambiguus (affecting cranial nerves IX and X) and the spinothalamic tract (involved in pain and temperature sensation). The most common causes include:

• Ischemic stroke due to occlusion of the posterior inferior cerebellar artery (PICA) or vertebral artery

• Brainstem tumors or lesions compressing the lateral medulla

• Demyelinating diseases such as multiple sclerosis (less common)

• Trauma or brainstem surgery affecting the medullary region

Symptoms

The hallmark of Avellis Syndrome is the combination of ipsilateral cranial nerve dysfunction and contralateral sensory deficits. Typical symptoms include:

Ipsilateral symptoms (same side as lesion):

• Paralysis of the soft palate – causing nasal speech and dysphagia (difficulty swallowing)

• Vocal cord paralysis – resulting in hoarseness or loss of voice (dysphonia)

• Deviation of the uvula away from the affected side

• Absent gag reflex on the affected side

Contralateral symptoms (opposite side of lesion):

• Loss of pain and temperature sensation on the body (but not the face), especially affecting the arm and leg

Facial pain and temperature sensation are usually spared, distinguishing it from more extensive medullary syndromes.

Diagnosis

Diagnosis of Avellis Syndrome relies on clinical neurological examination combined with neuroimaging to localize the lesion in the lateral medulla.

Diagnostic steps include:

• Neurological exam: Identifies asymmetrical cranial nerve deficits and sensory loss

• Magnetic Resonance Imaging (MRI): Best imaging modality to detect infarcts, demyelination, or tumors in the medulla

• Magnetic Resonance Angiography (MRA) or CT angiography: To evaluate vascular occlusion or stroke

• Brainstem auditory or evoked potentials: May be used in certain cases

Treatment

Treatment of Avellis Syndrome depends on the underlying cause and severity of symptoms. Management is both acute and supportive.

Acute treatment (for stroke-related cases):

• Thrombolytic therapy: If within the window period for ischemic stroke

• Antiplatelet agents: Such as aspirin or clopidogrel

• Anticoagulation: If cardioembolic source is suspected

Supportive and rehabilitative care:

• Speech and swallowing therapy: For dysphagia and dysphonia

• Nutritional support: Including feeding tube if necessary during recovery

• Pain management: For neuropathic pain if present

• Physical therapy: To manage contralateral motor or sensory deficits

Prognosis

The prognosis of Avellis Syndrome varies based on the extent of the brainstem lesion and the speed of diagnosis and treatment. Some patients recover partially or fully over time, while others may have persistent deficits.

Prognostic considerations:

• Recovery: Speech and swallowing function may improve with therapy over weeks to months

• Complications: Risk of aspiration pneumonia from impaired swallowing

• Rehabilitation: Plays a critical role in maximizing recovery and functional independence

Early diagnosis and intervention, especially in stroke cases, can significantly improve outcomes and reduce long-term disability.