Teaching Case

A 40-year-old woman presented with chronic low backache.

A 40-year-old woman presented with a history of chronic low backache for many years. There was new onset paresthesia in the bilateral lower limbs and difficulty in walking for the last 6 months, for which she sought medical attention. The patient did not complain of any bladder or bowel symptoms. Her clinical examination was unremarkable and routine haematological profile within normal limits. There was no significant illness in the recent past, however the patient had received repeated lumbar punctures during the treatment of meningitis about 20 years back. She was evaluated with a CT and noncontrast MRI of spine. Her CT examination revealed multiple areas of arachnoidal ossifications located at various levels, extending from D7 to D11 vertebral body (Figs. 1-4). On MR imaging these ossific areas demonstrated markedly T2-hypointense signal (Fig. 5). Based upon the typical imaging findings and relevant clinical history, a diagnosis of arachnoiditis ossificans was made.

Arachnoiditis ossificans (AO) is a rare variant of chronic arachnoiditis which is characterised by deposition of calcium or bone within the spinal arachnoid. The exact aetiopathogenesis is unknown, but is thought to be sequelae of end-stage chronic adhesive arachnoiditis. This can be sequelae of prior spinal surgery, spinal trauma, intraspinal haemorrhage, previous lumbar puncture or intra-thecal injection of steroids or anaesthetic agents. Fibroblastic proliferative response with associated osseous metaplasia is thought to be the causative factor. Thoracic spine is the most frequent to get involved, followed by the upper lumbar spine. The cauda equine nerve roots, unlike spinal arachnoiditis, are less commonly involved in arachnoiditis ossificans. Based upon the anatomical location and the clinical course, the entity has been classified into three types. Types I and II, usually involve the thoracic spine, and have progressive neurological symptoms often requiring surgical intervention. Type III involves the lumbar spine, presenting with less neurological symptoms, and usually can be managed conservatively.

Plain radiographs are insensitive to demonstrate intraspinal ossification. Myelography due to use of high density contrast medium is not a useful imaging modality in these patients. Non-contrast CT scan is considered the modality of choice. It is an invaluable tool to demonstrate these intrathecal ossific or calcific shells. Based upon the imaging and surgical findings, AO has been classified into three sub types: semicircular calcification/ ossification (Type-I), circular ossification (Type-II), and ossification enclosing cauda equina fibers (Type III). MRI is being increasingly used for evaluation of spinal disorders, but changes of AO can be subtle with a variable signal on T1-and T2-weighted images.

The clinical presentation is highly variable, symptoms ranging from a totally asymptomatic patient to incapacitating progressive compressive spinal myelopathy. Often these patients present with recurring backache with or without weakness of the limbs. The prognosis of this disease is variable. Some of the patients demonstrate neurological deterioration due to progressive compressive myelopathy; however others may remain relatively stable irrespective of the degree of intraspinal ossification. The treatment guidelines of arachnoiditis ossificans are controversial and not well established. Excision of the ossified intra-spinal plaques is not only technically difficult, but also has a poor clinical outcome. In patients with progressive neurological symptoms, simple decompression in the form of laminectomy has been reported to improve the neurological symptoms.