Ipsilaterally

Ipsilaterally is an adverb used in anatomy and medicine to indicate that a structure or finding occurs on the same side of the body as another reference point. The term derives from Latin ipsilateral, meaning “on the same side” (ipsi = same, lateralis = side). In clinical descriptions, ipsilateral is often contrasted with contralateral, meaning on the opposite side.

In practice, ipsilateral is used to describe relationships between anatomical structures or symptoms relative to a known lesion or landmark. For example, a facial nerve palsy is described as ipsilateral when the weakness occurs on the same side as the affected nerve. In neuroscience, many brain injuries produce contralateral motor or sensory deficits, but certain brainstem or cranial nerve injuries can cause ipsilateral cranial nerve findings. Imaging and surgical planning may reference an ipsilateral approach or findings on the ipsilateral side of a lesion.

Ambiguity can arise when the reference point is not explicit; writers should specify the reference structure (for example, “ipsilateral to the lesion” or “ipsilateral to the right hemisphere”) to avoid confusion. Related terms include contralateral and bilateral. Ipsilateral descriptions are common across clinical specialties, including neurology, radiology, and surgery, where side-specific localization informs diagnosis and treatment.