[A case of adult-onset neurenteric cyst presenting as chronic progressive muscular atrophy in lower legs].

A 50-year-old man was admitted, because of motor weakness of the lower limbs, dysesthesia of the left lower extremity, and anuresis. He had an episode of pain in his gluteal region 17 years ago, and then, no abnormalities were detected including myelography in a hospital, followed by slowly progressive muscular atrophy of his lower legs. At 50 years of age, dysuria appeared. He was diagnosed as having neurogenic bladder by urologists, and was admitted to our hospital. On admission, abnormal neurologic findings included: severe muscular atrophy in his lower legs, pes cavus, dysesthesia at the left S1 level, and autonomic bladder. Magnetic resonance imaging (MRI) showed mass lesion involving lower conus and cauda equina. After resection, pathological study revealed the mass was a neurenteric cyst. It is said that the neurenteric cyst causes an asymmetrical and sequential loss of specific neurological functions, with a subsequent return of these functions in the reverse order. That mechanism is not clear. However, in our case, the course of the illness was slowly progressive. We speculate that, because of the cyst's adhesion to cauda equina and perforation through the cyst by a nerve root, the cyst was fixed and caused slowly progressive neurological deficits in proportion to increase of the cyst's size. Our report suggests that a neurenteric cyst, involving the lower conus and cauda equina, can produce severe muscular atrophy in the lower legs.