We present a 30-year-old man with progressive spastic paraparesis. Spinal imaging revealed extensive calcification of the thoracic cord and cauda equina arachnoid, an intradural extramedullary cyst and evidence of rapidly progressing syringomyelia. Radiological diagnosis was arachnoiditis ossificans and an attempt at surgical decompression was made because of progressive neurologic deterioration. Due to tenacious adhesion of the calcified plaques to the cord and roots, only cyst drainage was achieved; the patient had no clinical improvement. A literature review revealed only two other cases reported in the literature with co-existence of arachnoiditis ossificans and syringomyelia. In none of the previous cases was there an intradural extramedullary arachnoid cyst, nor did the syrinx progress in such a rapid fashion. An attempt is made to explain possible pathophysiological mechanisms leading to this unusual pathology.