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The concept of perineural lymphatics is widely accepted, particularly in reference to prostatic carcinoma. A study of serial sections of many tissue blocks from 12 prostatic carcinomas revealed involvement of perineurium in only five cases; however, the assumption that these tumor cells are in lymphatics is unlikely because of the absence of an endothelial lining and the involvement of the entire circumference of the nerve by tumor in some instances. Experimental studies were performed to further investigate the perineurium. When India ink was injected into the lymphatics of the prostatic capsule of dogs, none was found in perineural areas either grossly or microscopically. Inoculation of Walker 256 carcinoma directly into the perineurium of femoral nerves of rats resulted in variable spread within the nerve and along tissue spaces in the perineurium, with no evidence of invasion of lymphatics or regional lymph nodes. Electron microscopy of canine and human nerves did not reveal any evidence of lymphatics in the perineurium. Therefore, the authors conclude that spread of malignant tumors along nerves in the prostate and elsewhere is not within performed lymphatics but within tissue planes of least resistance.

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