Biopsy of peripheral nerve is usually completed either as a full-thickness nerve biopsy (i.e., a complete transection of the nerve to remove a segment), or as a fascicular biopsy (i.e., a longitudinal dissection of the nerve to remove segments of only one or several fascicles), sparing at least a portion of the nerve. Full-thickness nerve biopsy is considered technically easier to perform and is preferable when the pathological evaluation should include both nerve fibers and surrounding connective tissue and vascular structures. Fascicular nerve biopsy usually produces a smaller deficit and is favored when larger nerves are biopsied. The choice of peripheral nerve biopsy site is limited by the potential deficits arising from nerve transection. The most common sites are the sural nerve or the superficial peroneal nerve, both subcutaneous sensory nerves in the lower extremity. In occasional cases, the superficial radial nerve in the upper extremity or the greater auricular nerve is also sampled. As noted earlier, concomitant biopsy of skeletal muscle to include small intramuscular nerve twigs may supplement the examination of the peripheral nervous system. Peripheral nerve biopsy may also be combined with skin biopsy, removing an ellipse of overlying skin, when morphological or tissue culture examination of skin is desired for diagnosis of metabolic or degenerative disease. The sample amount is varied and should be judged, on the one hand, by the amount of tissue needed for the proposed studies and, on the other hand, by the fact that deficits arising from transection of the nerve during biopsy will not necessarily be increased by removing the extra centimeter or two that transforms a nondiagnostic biopsy into a useful diagnostic tool. For most purposes, a 2- to 3-cm segment of full-thickness nerve or fascicles is adequate to provide tissue for standard light and electron microscopic examination, including preparation of teased nerve fibers and frozen section.
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