Approach to the Examination of the Cranial Nerves

The purpose of the examination of the cranial nerves is
to localize neurologic disease by looking for evidence of cranial nerve
dysfunction that can occur due to disorders of the brain, brainstem, or
cranial nerves themselves.

Assessment of the most diagnostically relevant cranial
nerve functions should be performed on all patients as part of any
standard neurologic examination. The examination elements that should
be checked routinely, the elements that usually can be skipped, and the
elements that need only be performed when specific clinical questions
are being asked are explained in subsequent chapters of this section
and summarized in Chapter 40, Performing a Complete Neurologic Examination.

All of the cranial nerves, with the exception of the
first (olfactory) and second (optic) nerves, have nuclei within the
brainstem and exit the brainstem to innervate their motor or sensory
structures (or both) in the head. The first and second nerves are
different than the others in that they are best thought of as
extensions of the brain; the optic nerves actually are central nervous
system structures.

The specifics of examining cranial nerve function are
described in subsequent chapters of this section. These chapters are
not categorized by individual cranial nerves; instead, each chapter
describes a functional examination

element.
For example, there is no chapter labeled “Examination of the Third
Cranial Nerve.” Instead, the assessment of function of the ophthalmic
nerve is imbedded within Chapter 14, Examination of Eye Movements, and Chapter 10, Examination of the Pupils, because these are the clinical tests that provide information about the function of this nerve.

Normally, patients should have intact motor or sensory function, or both, of each of the cranial nerves.

Cranial nerve dysfunction is manifested on examination
by weakness of the muscle(s) that the cranial nerve innervates or by
loss of sensory function in the distribution of the nerve. Chapters 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 and 23
describe the most common clinically relevant abnormal findings on
cranial nerve testing, explain which cranial nerve abnormalities cause
these findings, and address the potential diagnostic implications.

Try to approach your examination of the cranial nerves
by function, in the same manner that the following chapters in this
section are presented. Organize your cranial nerve examination by
functional components (e.g., pupillary function, eye movements, facial
strength) and then decide which of the cranial nerves is responsible
for any abnormal findings you detect on examination. Rote examination
of individual cranial nerves one by one is complicated and inefficient.