Experimental carcinomatous plexopathy.

To understand the pathophysiology of carcinomatous plexopathy better, we studied nerve lesions induced by an experimental thyroid carcinoma implanted over the brachial plexus in 30 Fisher rats. We performed a morphological study including light and electron microscopic examination and teased fibre preparations of brachial plexuses from implanted and control animals. The control side was normal in all. A large tumour always grew within 2 months in all implanted animals and a third of the rats eventually developed weakness of the corresponding anterior limb extremity. On gross examination the tumour always surrounded the brachial plexus, which showed a variety of microscopic abnormalities, ranging from isolated endoneurial oedema to total degeneration of nerve fibres in 41% of the implanted rats. The most frequent lesions consisted of segmental demyelination associated with endoneurial oedema at the site of compression. Some axons degenerated distally and regeneration by sprouting of the proximal stump was noted 80 days after implantation. All subpopulations of nerve fibres were equally affected. Invasion of the intrafascicular area by the tumour was an uncommon finding, in comparison with the constant entrapment of the branches of the plexus by the tumour. This invasion by the tumour induced demyelination of nerve fibres at the site of compression, and sometimes at a distance from the tumour. Regeneration did not occur when the tumour had invaded the intrafascicular area.(ABSTRACT TRUNCATED AT 250 WORDS)