Brown-Séquard syndrome

**Pathophysiology (tract anatomy is the key to the question):** - **Dorsal columns (fasciculus gracilis/cuneatus):** carry fine touch, vibration, and proprioception. They ascend ipsilaterally and decussate in the medulla. A lesion causes **ipsilateral** loss below the lesion. - **Lateral corticospinal tract:** carries motor fibers that decussate in the caudal medulla (pyramids). A lesion causes **ipsilateral** spastic paralysis below the lesion (UMN signs: hyperreflexia, increased tone, positive Babinski). - **Spinothalamic tract:** carries pain and temperature (and crude touch). Fibers enter and decussate within 1-2 segments via the anterior white commissure, then ascend. A lesion causes **contralateral** loss of pain and temperature, starting 1-2 levels below the lesion.

**Findings at the level of the lesion (ipsilateral):** - LMN signs: flaccid paralysis, atrophy, and loss of reflexes in that myotome (anterior horn or root damage). - Loss of all sensory modalities in that dermatome (dorsal root or entry zone damage). - Band of segmental anesthesia. - If the lesion is at T1 or above, ipsilateral Horner syndrome (ptosis, miosis, anhidrosis) from damage to descending sympathetic fibers.

**Findings below the lesion:** - Ipsilateral: spastic weakness/paralysis, loss of proprioception, vibration, and fine touch. - Contralateral: loss of pain and temperature. - Light (crude) touch is usually preserved overall because it travels in both the dorsal columns and the spinothalamic tract.

**Etiologies:** - Penetrating trauma (stab or gunshot wounds) is the classic cause. - Extramedullary compressive lesions: tumors (e.g., meningioma, schwannoma, metastases), disc herniation, epidural hematoma or abscess, vertebral fracture. - Multiple sclerosis and other demyelinating disease. - Radiation myelopathy, decompression sickness, and transverse myelitis (less common). - A pure hemisection is rare; most cases are "Brown-Séquard-plus" (incomplete).

**Diagnosis and management:** - MRI of the spine is the imaging test of choice. - Treat the underlying cause: surgical decompression for compression, high-dose steroids for demyelination/inflammation, and antibiotics plus drainage for abscess. - Rehabilitation is important. Prognosis is relatively good compared with other incomplete cord syndromes, and most patients regain ambulation.

**Differentiating from other cord syndromes (high-yield):** - **Anterior cord syndrome:** loss of motor, pain, and temperature bilaterally below the lesion, with preserved dorsal column function (vibration, proprioception). Caused by anterior spinal artery infarct. - **Central cord syndrome:** "cape-like" loss of pain and temperature, with greater weakness in the upper than lower extremities. Seen with hyperextension injury in older adults with cervical spondylosis, and with syringomyelia. - **Posterior cord syndrome:** isolated loss of proprioception and vibration (e.g., tabes dorsalis in tertiary syphilis, vitamin B12 deficiency/subacute combined degeneration). - **Cauda equina syndrome:** LMN signs, saddle anesthesia, urinary retention.

**Board pearl:** Remember that the lesion is ipsilateral for everything except pain and temperature, which are contralateral. A stem describing a stab wound to the back with ipsilateral leg weakness and loss of vibration sense, plus contralateral loss of pinprick, is Brown-Séquard until proven otherwise.