| Lesion location | Causes | Common concurrent neurologic abnormalities | Diagnostic plan |
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| Brainstem | Neoplasia, encephalitis, vascular, trauma | Altered mental status, ipsilateral hemiparesis, ipsilateral postural reaction deficits | MRI; CSF analysis | | C1–T3 spinal cord | IVDH, trauma, neoplasia, FCE | Ipsilateral or bilateral hemiparesis/plegia, ± reduced reflexes to thoracic limbs, normal mentation | MRI preferred, myelogram also may show lesion. CSF analysis | | T1–T3 nerve roots | Brachial plexus avulsion, peripheral nerve tumor (lymphoma, nerve sheath tumor most common) | Ipsilateral loss of thoracicl imb reflexes,ipsilateral loss of cutneous trunci, ipsilateral monoparesis/plegai, absent postural reactions in affected thoracic limb only | MRI, electrodiagnostic testing | | Sympathetic trunk, cranial cervical ganglion* | Trauma, iatrogenic following jugular venipuncture, mediastinal or thyroid neoplasia | Possibly laryngeal dysfunction | Neck ultrasound, MRI, thoracic radiographs | | Tympanic bulla | Otitis media, polyp (cat), neoplasia, trauma | Ipsilateral vestibular disease, ipsilateral facial nerve paralysis | MRI, CT, bulla radiographs, myringotomy | | Retrobulbar | Neoplasia, abcess, trauma | None, or dysfunction of CN II, III, IV, and VI. | MRI, orbital ultrasound |
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