Fig. 5.
Microscopic image of deliberate intraneural injection into median nerve. The compact internal structure of the nerve did not permit the injection of diluted heparinized blood between the fascicles (F), into the perineurium, or inside the fascicles. In this case, the entire structure is compact and not only the contents of the fascicles. This occurs due to the absence of adipocytes between the fascicles. This absence prevents the spread of the marker between the fascicles. In this sample, the tissue between the fascicles was formed by collagen fibers without any adipocytes. We can see the complete median nerve with no intraneural diluted heparinized blood. The diluted heparinized blood is completely contained in the subcircumneural space (1), and it did it cross the epineurium (Ep). This is a true subcircumneural injection, which, on ultrasound, appeared similar to intraneural (subepineural) injection. Tissue between the fascicles (interfascicular tissue) is shown as (4). (A) The circumneuria (C) include the artery (2), vein (3), and nerve. Diluted heparinized blood spread around all of these structures without penetrating it. This is the neurovascular bundle. (B and C) Interfascicular (4; between the fascicles) and intrafascicular tissue (5; inside the fascicles—endoneurium [En]) as well as the perineurium (P) did not contain any diluted heparinized blood. Small red spot (white arrow) is an artifact—it is translucent. (D) Scanning electron microscopy image of the endoneurium of a peripheral nerve. It shows the axons (white), myelin sheaths (light green), and the endoneurial matrix (light purple). What appear like channels or spaces in the endoneurium and between the endoneurium and the myelin sheaths (white arrows) are in fact artifacts formed by the processing of the slide. Magnification: A, ×40; B, ×200; C, ×240; D, ×1,500. Stain: hematoxylin and eosin.