PATTERNS OF ANTERIOR SPINAL-CANAL INVOLVEMENT BY NEOPLASMS AND INFECTIONS

PURPOSE: To show that retrovertebral extension of neoplastic and infec tious disease proceeds in a predictable manner, with the anatomic supe rstructure determining the shape of the advancing process. METHODS: We examined 58 patients who had neoplastic (n = 44) and infectious (n = 14) processes that caused canal compromise. In total, 140 levels were examined by means of MR imaging only (48 patients), CT only (1 patient ), CT plus MR imaging (3 patients), and MR imaging plus CT myelography (6 patients). RESULTS: At 136 levels, the retrovertebral disease proc ess took the shape of a smoothly marginated, bilobulated mass that was broad-based against the posterior surface of the vertebra. Various de grees of mass effect were observed: symmetric on 108 levels and asymme tric on 28 levels; on 4 levels, expansion of the anterior epidural spa ce was unilobar, reflecting unilateral canal invasion. With advanced s tages of canal invasion, this bilobulated pattern was maintained but t here was a tendency toward detachment of the midline septum (20 levels ). CONCLUSION: The observed patterns are determined by the particular anatomy of the anterior epidural space. The shape of the mass is impos ed by the posterior longitudinal ligament and by the attached lateral membranes, with the central tether produced by the attached midline se ptum. The two compartments expand independently.