Ipsilateral

Ipsilateral refers to structures or effects that occur on the same side of the body as a reference point. The term comes from Latin, with ipsi meaning “same” and latus meaning “side.” It is commonly used in anatomy, physiology, and clinical medicine to describe spatial relationships, in contrast to contralateral, which means on the opposite side, and to unilateral or bilateral, which describe one side or both sides, respectively.

In clinical and anatomical contexts, ipsilateral is used to localize symptoms and lesions. For example, a peripheral facial nerve (cranial nerve VII) lesion causes ipsilateral facial weakness, affecting the same side as the nerve injury. In spinal cord syndromes, Brown-Sequard syndrome typically presents with ipsilateral motor loss and loss of vibratory/proprioceptive sensation, along with contralateral loss of pain and temperature below the level of the lesion. In ophthalmology, damage to the optic nerve results in ipsilateral blindness in the affected eye.

Understanding ipsilateral versus contralateral relationships aids in diagnosing and localizing pathology. Some conditions may involve both concepts depending on the anatomical pathways involved; for instance, many motor pathways decussate, leading to contralateral body symptoms, while certain cranial nerve–level or localized lesions yield ipsilateral signs.

See also: contralateral, unilateral, bilateral, decussation.