This review was undertaken to stress the ever-present possibility of serious error in the diagnosis of low-back conditions, and to emphasize the difficulties in the diagnosis of cauda equina lesions.

Forty-eight cases of tumor of the cauda equina or low spinal cord are reported in which operation was performed at the Lahey Clinic between 1939 and 1948. In this same time interval, 1,056 intervertebral-disc operations were performed. The tumors represent 4.3 per cent. of the entire group. The patients with tumors ranged in age from fourteen to sixty-eight years; the numbers of males and females were equal.

Early diagnosis is of paramount importance in the tumor cases. There is great similarity in the clinical picture of tumors of the cauda equina and disc lesions.

Insidious onset of pain with an unremitting course definitely suggests tumor. Numbness and weakness of the legs is more often associated with tumor. The duration of symptoms varies from two months to eight years. The most common first complaint was low-back pain, but 12 per cent. of the patients had no pain whatsoever.

The most common physical sign in the tumor cases was an absent or diminished ankle jerk, but this finding is common in disc lesions, also. Tumor lesions cannot usually be differentiated from disc lesions by physical signs. In 8 per cent. of the tumor cases, neurological signs were not present.

The myelogram is the most significant and valuable aid in the differential diagnosis. The use of pantopaque, removed at the time of fluoroscopy, is preferred at the present time.

Estimations of total protein ranged from 14 to 610 milligrams per 100 cubic centimeters, the average being 140. A protein determination of over 100 definitely suggests tumor and is a valuable diagnostic aid. However, in 30 per cent. of the patients who had tumors, the total protein was not elevated.

In this series, 20 per cent. of the tumors were malignant. Of the benign tumors, neurilemmoma was by far the most common, with ependymoma second.