Post traumatic arachnoiditis ossificans.

Arachnoiditis ossificans is a rare chronic disorder characterized by the presence of calcification/ ossification of the spinal arachnoid. We describe the computed tomography (CT) and magnetic resonance imaging (MRI) findings of arachnoiditis ossificans as sequelae to trauma in a 30-year-old patient. This imaging diagnosis becomes important to alert the clinician as most of them can be treated by conservative management.

INTRODUCTION

Arachnoiditis ossificans represents chronic arachnoiditis characterized by calcification and/or ossification.[1] Unlike adhesive arachnoiditis, arachnoiditis ossificans can be treated with surgery[2] in patients with severe or deteriorating symptoms. However, surgery remains a controversial treatment option because excision of the dural calcification and microsurgical neurolysis is technically difficult, particularly when multiple nerve roots are involved and even if surgical removal of the intrathecal ossification is possible, the clinical outcome is generally poor. We analyze the clinical symptoms, radiological findings, and treatment options in a patient diagnosed of post traumatic arachnoiditis ossificans with a brief review of literature.

CASE REPORT

A 21-year-old male who sustained an injury in a fall from a tree 2 years back, presented with history of chronic progressive low back pain and left foot drop. There was no evidence of myelopathy. Higher mental functions, tone, power of the limbs were normal. There were no other neurological deficits. Radiograph of LS-spine showed only burst fracture of L4 vertebra. Non-contrast CT revealed a burst fracture of L4 vertebra with mild posterior retropulsion. There were intrathecal ossifications in the spinal canal extending from L4-S2 level with nerve roots exiting through the ossifications. These features are suggestive of arachnoiditis ossificans [Figure 1 a–d].

Figure 1

(a) Non-contrast sagittal CT shows a burst fracture of L4 vertebra with mild posterior retropulsion. (b, c and d): Non-contrast axial CT showing intrathecal ossifications in the spinal canal extending from L4-S2 level with nerve roots exiting through the ossifications

MRI was also done to see if there was any associated clumping of nerve roots/any associated pathology. MRI showed the burst fracture of L4 vertebra. On T1 images, the intrathecal ossification was hyperintense on T1 images and hypointense on T2 images [Figure 2a and b]. There was no clumping of nerve roots at any level. Since the patient declined surgery, conservative management for pain and physiotherapy was offered.

Figure 2

(a and b): Sagittal MRI sWequences show the intrathecal ossification, which is hyperintense on T1 images (arrows) and hypointense on T2 images

DISCUSSION

Arachnoiditis ossificans is an unusual chronic meningeal inflammatory process that typically affects adults[3] and is thought to be sequelae of end-stage adhesive arachnoiditis. Kaufman and Dunsmore[4] in 1971 coined the term arachnoiditis ossificans. Till 1998, only 46 cases were reported in the world literature[2] with only a handful of cases reported after that. To our knowledge, until now no cases have been reported from the Indian subcontinent, which describe the CT and MRI findings in arachnoiditis ossificans. Most of these patients present with neurological deficits like inability to walk due to lower limb weakness, although some of them may be asymptomatic.[1]

Prior trauma, as in this case, is a rarely reported cause for arachnoiditis ossificans. Surgery, subarachnoid hemorrhage, myelography (particularly using oil-based contrast agents), and spinal anesthesia have been more commonly implicated as causative factors of arachnoiditis ossificans.[1]

Osseous metaplasia associated with chronic inflammation is probably the most likely cause, with arachnoiditis ossificans representing end-stage chronic arachnoiditis, as suggested by Kaufman and Dunsmore.[1] They found chronic fibroblastic proliferative change to the leptomeninges associated with osseous metaplasia in all the cases they reviewed. They also suggested that vascular shunting or pressure effects might contribute to the development of the disorder, possibly complicated by bleeding into the abnormal tissues.[1] Various other mechanisms proposed for the development of the ossification include intradural hematoma, which organizes and ossifies the seeded bone fragments.[1]

In our case, the burst fracture of L4 vertebral body shows posterior cortical breech, and thus the seeded bony fragments might have resulted in chronic inflammatory reaction over a period of two years, which led to arachnoiditis ossificans for which the patient presented with the history of progressive neurological deficit.

Unenhanced CT is sensitive to diagnose this disorder and is also useful to evaluate the full extension of the ossified mass if surgical intervention is needed. On MR imaging, the findings could be minimal. There can be nerve root clumping, which is best demonstrated on axial T2-weighted images. The arachnoid calcification is difficult to identify using MRI because of their variable signal intensities. They can be hypointense or hyperintense in T1-weighted images and in T2-weighted images, and the calcifications or ossifications can vary from hypointense to hyperintense. Thus, it is important to verify the arachnoid ossification by CT scan, if arachnoiditis ossificans is suspected in the MRI scan. MR appearances of arachnoiditis ossificans has gained more significance because of the decline in the use of CT with corresponding rise in the use of MR imaging for the assessment of low back pain by the present day radiologist. MRI is also important to assess associated pathologic conditions like arachnoid cysts, intramedullary cysts and syringomyelia.[5] Conventional radiographs rarely show the abnormality unless it is extensive, and thus CT is the imaging modality of choice.

The best treatment strategy for arachnoiditis ossificans has still not been established. If the symptoms are mild, the outcome with conservative management is good and the patients become symptom-free over a period of time. In patients with severe or deteriorating symptoms, surgery is often performed.[6]

Excision of the dural calcification and microsurgical neurolysis is technically difficult, especially when multiple nerve roots are involved. Even if the surgical removal of the intrathecal ossification is possible, the clinical result reported is generally poor.[7]

Procedures such as decompressive laminectomies, anterior fusion, and foraminotomies are recommended and good results have been reported.[7] Only 50% of patients managed with surgical intervention showed improvement in the cases reported in the literature.[8] Treatment decisions are also based on the location and morphology of the calcifications and in relation to compression of the spinal cord or nerve roots.[2]

CONCLUSION

Arachnoiditis ossificans is a rare entity. CT is the imaging modality of choice to evaluate the full extension of the ossified mass. MRI is needed to assess associated pathologic conditions, clumping of nerve roots and to differentiate a compressive mass lesion which simulates arachnoiditis ossificans. If the symptoms are mild, conservative management is recommended. In patients with severe or deteriorating symptoms, surgery is often performed and even with surgical removal, the clinical outcome is generally poor.