Arachnoiditis ossificans

Case contributed by Dr Noriza Zainol Abidin


Elderly man with a history of a traumatic compression fracture of the L1 vertebra post posterior instrumentation 20 years ago. Progressive lower limb weakness. He sustained a left intertrochanteric fracture.

Patient Data

Age: 75 years old
Gender: Male

Metal artefacts from posterior instrumentation traversing T12 and L2 lamina bilaterally fixing an old L1 vertebral fracture.

Diffuse dense curvilinear calcifications are seen along the anterior spinal dura mater extending from L1 till L5 level. Multiple intrathecal calcifications suggestive of cauda equina ossifications. Some of the intrathecal calcifications follow the course of traversing nerve roots.

Left intertrochanteric fracture with large surrounding subacute hematoma concordant with a recent history of fracture.


MRI Lumbosacral

Coronal T2- weighted images shows diffuse abnormal circumferential thickening of thecal sac with blooming artefact, concordant with dural calcifications seen on CT images.

Axial T2-weighted images show displacement of the nerve roots of the cauda equina in the initial images. Abnormal thickening and clumping of the cauda equina with intrathecal hypointense signal abnormality seen at distal lumbar, consistent with sequelae of arachnoiditis.

Well defined hyperintense lesion within L4 vertebra body in keeping with a vertebral hemangioma.

Based on CT and MRI findings, features consistent with arachnoiditis ossificans.

Case Discussion

Arachnoiditis ossificans is an unusual chronic meningeal inflammatory process and is thought to be the sequela of end-stage adhesive arachnoiditis.

Common causative factors include surgery, arachnoid hemorrhage, myelography (particularly oil-based contrast agents), and spinal anesthesia.

CT and MRI are complementary imaging techniques. 

CT is the best investigation tool to visualize the ossified intraspinal lesion and nerve roots. The findings of ossified intrathecal lesions are specific and diagnostic. As in this case, there is curvilinear dural calcifications, intrathecal coarse calcifications and ossified individual nerve roots adhered to the posterior thecal sac.

The MR imaging is favourable in depicting arachnoiditis. The sign includes central clumping of nerve roots, peripheral adhesion of the nerve roots and intradural cysts due to loculation of the subarachnoid spaces.

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Case information

rID: 51394
Published: 13th Apr 2017
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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