—True neuromas spring from the structures of nerve trunks, which trunks may also be the site of other tumors, mainly fibromas and sarcomas, with which neuromas may be easily confounded. The most common nerve tumor is the neurofibroma, which grows from the structure of a nerve sheath, its long axis usually coinciding with that of the nerve trunk. Tumors of this class vary greatly in size, are often multiple, and in other instances affect nearly all the nerves in the body. They are extremely liable to myxomatous degeneration, which will account for many of the instances reported as myxoneuroma, etc. They attack cranial and spinal nerves alike, and no nerve or nerve root in the body is exempt. The sensory nerves appear more liable to attack than the motor. The nerve least often attacked is the optic. They are not rare upon the roots of the spinal nerves, in which location they may attain to such size as to press upon the cord and induce paraplegia. Multiple neuromas are often associated with [molluscum fibrosum] (q. v.). There is an instance on record in which 1600 of these tumors were found after careful dissection of the neuroskeleton, and another in which at least 2000 were found, 60 of them involving the pneumogastric trunks and their branches.
Fig. 84
Plexiform neuroma, dissected free from all adherent tissues. (Lexer.)
Fig. 85
Plexiform neuroma of chest wall in a young child. Illustrating its gross external resemblance to lymphangioma. (Lexer.)
Plexiform Neuroma.
—Plexiform neuroma is relatively rare. This is a type of nerve tumor in which all the branches of a given nerve which are distributed to a particular area become enlarged and elongated, the overlying skin being stretched and thin. Such a tumor seems like a loose bag containing a number of vermiform bodies, resembling the sensation given when palpating a varicocele. On section each of the affected nerves reveals a quantity of myxomatous tissue replacing the nerve sheath. They are in large measure congenital. The skin overlying a plexiform neuroma will frequently be found to be pigmented, variously altered in thickness, and covered with fine hair. These growths have been frequently mistaken for lymphangioma ([Figs. 84] and [85]).
Malignant Neuroma.