[Adipose tissue within peripheral nerves. Study of the human sciatic nerve].

Aim: To describe the distribution of intraneural adipose cells in relation to nerve fascicles in a portion of peripheral nerve usually involved in accomplishing an anesthetic blockade of a lower extremity.

Method: Using a scanning electron microscope, we studied sciatic nerve samples from the point of amputation of a lower limb of three patients. The samples were obtained at the upper angle of the popliteal fossa, 10-15 cm cephalad to the knee joint line.

Results: During dissection of the sciatic nerve samples, we observed a solitary trunk, but examination of the cross-sections under the microscope revealed the components of two clearly separated branches joined by supporting tissue. The sciatic nerve had an oval form in the portion under study, measuring 6.5 to 7.5 mm by 3.6 to 3.9 mm. Between the fascicles, the adipose tissue varied in thickness from 0.5 mm in the central zones to 0.2 mm in the peripheral zones. The adipocytes, which were all similar in the size with diameters of 40 microns, were empty, as a result of elimination of the lipid vacuoles during fixation. The adipose tissue was distributed inside the epineurium to surround isolated fascicles or groups of fascicles.

Conclusions: The adipose tissue inside a nerve surrounded the fascicles to form adipose sheaths that separated the fascicles from one another. The thicknesses of these adipose sheaths varied from one fascicle to another. Cells join to make it possible to create a compact adipose sheet that can delay the diffusion of local anesthetic injected near a nerve and that can therefore interfere with the characteristics of an anesthetic blockade.