THE PATHOLOGY OF NEURAL-ARCH DEFECTS

A Dissection Study

¹ Departments of Surgery and Anatomy, Washington University School of Medicine, St. Louis

In discussing the relative significance of neural-arch defects and split spinous processes (bifid spines), Willis stated: "When the defect destroys the integrity of that portion of the bony arch between the vertebral body and the inferior articular processes as in the case of a bilaterally separate neural arch the condition is much more serious. Here we have the anchorage of the spine depending merely upon a fibrocartilaginous union with ligamentous and muscular support." Again, "Rupture of the synchondrosis [defect] is more serious than the ligamentous injury which accompanies it. The separated bone ends are covered with cartilaginous material and, therefore, show no tendency to reunite." In this particular specimen, the defect in the isthmus on the right was united not by fibrocartilage, but by unusually strong fibrous ligaments, and was ensheathed in a fibrous capsule. The isthmus on the left was completely absent, and there was no evidence of fibrocartilaginous replacement. The pseudo-articulations between the pedicles, and the abnormal prolongations of the cephalad portions of the laminae, were effected by ligaments and not by cartilage.

Findings in this specimen were: (a) the complete absence of an isthmus on one side, and, on the other side, a defective isthmus strongly fixed by ligaments and three times the length of the normal isthmus above; (b) the abnormal conformations of the laminae and their pseudo-articulations with the pedicles; (c) the structural variations noted in the ligamentum flavum on each side; and (d) the associated presence of a partial developmental lumbarization of the first sacral segment and a sacralization of the first coccygeal segment.

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