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Arachnoiditis Ossificans
Peer-Review Short Reports
Arachnoiditis Ossificans Harshpal Singh, Scott A. Meyer, Madhu R. Jannapureddy, Nirit Weiss
Key words 䡲 Arachnoid cyst 䡲 Arachnoiditis ossificans Abbreviations and Acronyms CT: Computed tomography MRI: Magnetic resonance imaging Department of Neurosurgery, Mount Sinai School of Medicine, New York, New York, USA To whom correspondence should be addressed: Nirit Weiss, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2011) 76, 5:478.e12-478.e14. DOI: 10.1016/j.wneu.2010.12.001 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2011 Elsevier Inc. All rights reserved.
CLINICAL PRESENTATION An 81-year-old woman presented with a 1-year history of mid-back pain; 3 months of rapidly progressive bilateral lower extremity weakness, numbness, dysesthetic pains; and urinary incontinence. On examination, she was found to have proximal lower extremity weakness, a T8 sensory level, and bilateral upgoing toes. Upper extremities were normal. She had no history of previous trauma.
䡲 OBJECTIVE: Arachnoiditis ossificans is an uncommon clinical entity in which arachnoid ossification leads to clinical symptomatology. In this case report, we describe the case of a myelopathic patient with arachnoid ossifications, an arachnoid cyst, and syringomyelia coexisting with a herniated thoracic disc at the same levels. 䡲 CASE DESCRIPTION: An 81-year-old woman presented with rapidly progressive leg weakness, dysesthetic pains, and urinary incontinence. 䡲 RESULTS: The patient underwent thoracic laminectomy with costotransversectomy for resection of ossified arachnoid and re-establishment of cerebrospinal fluid pathways. 䡲 CONCLUSION: Altered cerebrospinal fluid dynamics secondary to the obstruction in subarachnoid flow may predispose to the formation of an arachnoid cyst, and the cyst itself may be the proximate cause of the myelopathy.
transition. There was immediate filling of the subarachnoid space cranial to T8, and complete myelographic block caudal to this level (Figure 2). There was no obvious heterotopic calcification seen surrounding the spinal cord (Figure 3). Given these radiographic findings, the surgical approach was altered from a thoracoscopic T6-7 discectomy to that of a posterolateral approach, facilitating intradural exploration as well as discectomy.
SURGICAL INTERVENTION The patient was positioned prone, and a T6-T8 laminectomy was performed. Intradural exploration revealed a large, compressive arachnoid cyst cranial to T8, and thick, ossified arachnoid circumferentially encasing the spinal cord, spanning the T6-T8 levels and filling the entire subdural space caudal to this level (Figure 4). The arachnoid cyst was decompressed, and a
IMAGING FINDINGS Magnetic resonance imaging (MRI) of the spine was significant for a central T6-T7 disc herniation with significant spinal cord compression. Distal to the disc herniation, the spinal cord appeared abnormally enlarged, and a syrinx was present from T6 to the conus (Figure 1A). Initially, the patient appeared to have typical spinal cord compression caused by disc herniation. On closer inspection, however, the transition from compressed to dilated cord appeared unusually abrupt, and the possibility of a dorsal intradural arachnoid cyst displacing the spinal cord anteriorly was considered (Figure 1B). Computed tomography (CT) and a CT myelogram were performed, which demonstrated again this sharp
478.e12
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Figure 1. Preoperative magnetic resonance image with axial T2 (A) and sagittal T2 (B) slices.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.12.001
PEER-REVIEW SHORT REPORTS HARSHPAL SINGH ET AL.
ARACHNOIDITIS OSSIFICANS
Figure 2. Myelogram showing block at the T8 level.
central dorsal channel of the ossified arachnoid was removed in an attempt to re-establish normal cerebrospinal fluid flow caudal to T8. The entire ossification could not be removed because of the adherence of the ossification to the cord and vasculature. A right unilateral costotransversectomy was performed to gain anterior access and perform the discectomy, although at this point, under direct visualization, the disc no longer appeared to be compressing the cord. Of note, the motor evoked potential nearly doubled in amplitude after the arachnoid cyst and ossified arachnoid were removed and before discectomy. No direct drainage of the syrinx was attempted. A dural graft was sewn in place to maintain an enlarged intrathecal space, allowing for normalization of cerebrospinal fluid flow. Histological evaluation of the ossified arachnoid tissue was consistent with densely calcified lamellar bone (Figure 5).
POSTSURGICAL COURSE The patient progressively improved to independent ambulation as well as resolution of her incontinence. The syrinx also significantly improved as demonstrated by the 1-year postoperative MRI (Figure 6). However, although improved, the burning dysesthetic-type pains persist.
DISCUSSION AND CONCLUSION Incidental leptomeningeal calcifications are common. Autopsy studies reveal 6% to 76% incidence (1, 4). These are thought to be secondary to a degenerative process. Arachnoiditis ossificans, on the other hand, is present when arachnoid ossification leads to clinical symptomatology. Dense calcifi-
Figure 3. Axial (A) and sagittal (B) computed tomographic myelogram showing imaging characteristics not suggestive of arachnoid calcification.
cation and metaplastic ossification of the arachnoid is thought to be secondary to degeneration or chronic inflammation of arachnoid cell clusters. Initiating factors such as trauma, surgery, or myelography leading to arachnoiditis are postulated. A few case reports and case series describe the clinical manifestations of this process, typically myelopathy caused by thoracic spinal cord compression/ischemia, or cauda equina syndrome caused by lower lumbar ossification (3, 6). Two previous case reports describe the development of syringomyelia secondary to arachnoiditis ossificans (3, 5). In one of these, an arachnoid cyst also developed, and was thought to be a significant contributor to the clinical deterioration. A spiral CT scan is thought to be the optimal radiographic study for demonstrating the ossified arachnoid plaques. In this report, we present the case of a woman who developed a rapidly progressive thoracic myelopathy, localizable to the mid-thoracic spine. A T6-T7 central disc herniation with significant anterior spinal cord compression was identified on MRI imaging. This was adequate to explain the myelopathy and syringomyelia, and thus no preoperative, nonmyelographic CT scan was performed. However, both MRI and CT myelogram did suggest a superimposed anterior displacement of the spinal cord, presumably from an arachnoid cyst, and thus intradural exploration was undertaken, leading to the diagnosis. This report is significant for several reasons. The first is the illustration of the coexistence of multiple anatomic abnormalities at the same spinal levels. The initial diagno-
WORLD NEUROSURGERY 76 [5]: 478.e12-478.e14, NOVEMBER 2011
sis of disc herniation might have led to a lateral surgical approach via thoracotomy. This procedure would not have addressed the patient’s true pathology, and might have been dangerous in the presence of the cyst and ossifications. Once the cyst had been decompressed, and a channel established through the ossification, the motor potentials doubled in amplitude and the anterior disc was visualized to no longer have a compressive component. Although the pathologic evaluation demonstrated mature lamellar bone, it is noteworthy that the CT scan did not demonstrate dense circumferential calcification around the spinal cord. Previous reports have stated that the most reliable diagnostic test for arachnoiditis ossificans is noncontrast CT (2). This case demonstrates that the diagnosis cannot be excluded entirely based on a CT scan. Although the vast majority of arachnoid calcifications are not clinically significant,
Figure 4. Intraoperative image showing calcified arachnoid held by forceps with exposed spinal cord underneath.
www.WORLDNEUROSURGERY.org
478.e13
PEER-REVIEW SHORT REPORTS HARSHPAL SINGH ET AL.
ARACHNOIDITIS OSSIFICANS
Figure 5. Hematoxylin and eosin stain (original magnification ⫻5) showing densely calcified lamellar bone.
the term arachnoiditis ossificans implies clinical deterioration caused by these plaques. There has been some discussion with respect to the underlying cause of the deterioration. It is typically thought to be secondary to direct spinal cord compression caused by the space-filling mass. Resection of the mass is usually attempted, with mixed or poor results. This is likely because of the adherence of the ossification to the substance of the cord itself, requiring significant intraoperative manipulation in often unsuccessful attempts to remove it. In
this case, although there was a very large circumferential mass of bone lining the cord, marsupialization of the arachnoid cyst alone was adequate to cause a doubling in the amplitude of the motor evoked potential. The patient clinically improved despite a partial resection of the mass. This suggests that direct compression caused by the calcifications may not be the primary cause of the myelopathy. The altered cerebrospinal fluid dynamics secondary to the obstruction in subarachnoid flow may predispose to the formation of an arachnoid cyst,
and the cyst itself may be the proximate cause of the myelopathy. Drainage of the cyst leads to rapid decompression of the spinal cord, whereas reestablishing cerebrospinal fluid flow by creating the channel may help to prevent recurrence of the cyst. In the 2 earlier reports in patients with arachnoiditis ossificans and syringomyelia, the syrinx was directly drained at the time of surgery. In this case, the syrinx was presumed to be secondary to altered flow, with direct compression from the arachnoid cyst leading to ischemic changes. Therefore, it was not directly drained, and was itself treated by reestablishing normalized subarachnoid flow. The decreasing postoperative size of the syrinx supports this course of action. Arachnoiditis ossificans remains a rare cause of myelopathy in patients. Unfortunately, the clinical outcomes after surgery have been quite disappointing. A greater understanding of the dynamics leading to the clinical presentation may help direct treatment for these patients.
REFERENCES 1. Herren RY: Occurrence and distribution of calcified plaques in the spinal arachnoid in man. Arch Neurol Psychiatry 41:1180-1186, 1939. 2. Jaspan T, Preston BJ, Mulholland RC, Webb JK: The CT appearances of arachnoiditis ossificans. Spine 15: 148-151, 1990. 3. Kahler RJ, Knuckey NW, Davis S: Arachnoiditis ossificans and syringomyelia: a unique case report. J Clin Neurosci 7:66-68, 2000. 4. Morrison RL, Cob S, Bauer W: The effect of advancing age upon the human spinal cord. Boston: Harvard University Press; 1959:40-41. 5. Nagpal RD, Gokhale SD, Parikh VR: Ossification of spinal arachnoid with unrelated syringomyelia. J Neurosurg 42:222-225, 1975. 6. Papavlasopoulos F, Stranjalis G, Kouyialis AT, Korfias S, Sakas D: Arachnoiditis ossificans with progressive syringomyelia and spinal arachnoid cyst. J Clin Neurosci 14:572-576, 2007. Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. received 07 June 2010; accepted 01 December 2010 Citation: World Neurosurg. (2011) 76, 5:478.e12-478.e14. DOI: 10.1016/j.wneu.2010.12.001 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
Figure 6. One-year postoperative axial (A) and sagittal (B) magnetic resonance images showing reduction in syrinx size.
478.e14
www.SCIENCEDIRECT.com
1878-8750/$ - see front matter © 2011 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.12.001
Arachnoiditis Ossificans Harshpal Singh, Scott A. Meyer, Madhu R. Jannapureddy, Nirit Weiss
Key words 䡲 Arachnoid cyst 䡲 Arachnoiditis ossificans Abbreviations and Acronyms CT: Computed tomography MRI: Magnetic resonance imaging Department of Neurosurgery, Mount Sinai School of Medicine, New York, New York, USA To whom correspondence should be addressed: Nirit Weiss, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2011) 76, 5:478.e12-478.e14. DOI: 10.1016/j.wneu.2010.12.001 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter © 2011 Elsevier Inc. All rights reserved.
CLINICAL PRESENTATION An 81-year-old woman presented with a 1-year history of mid-back pain; 3 months of rapidly progressive bilateral lower extremity weakness, numbness, dysesthetic pains; and urinary incontinence. On examination, she was found to have proximal lower extremity weakness, a T8 sensory level, and bilateral upgoing toes. Upper extremities were normal. She had no history of previous trauma.
䡲 OBJECTIVE: Arachnoiditis ossificans is an uncommon clinical entity in which arachnoid ossification leads to clinical symptomatology. In this case report, we describe the case of a myelopathic patient with arachnoid ossifications, an arachnoid cyst, and syringomyelia coexisting with a herniated thoracic disc at the same levels. 䡲 CASE DESCRIPTION: An 81-year-old woman presented with rapidly progressive leg weakness, dysesthetic pains, and urinary incontinence. 䡲 RESULTS: The patient underwent thoracic laminectomy with costotransversectomy for resection of ossified arachnoid and re-establishment of cerebrospinal fluid pathways. 䡲 CONCLUSION: Altered cerebrospinal fluid dynamics secondary to the obstruction in subarachnoid flow may predispose to the formation of an arachnoid cyst, and the cyst itself may be the proximate cause of the myelopathy.
transition. There was immediate filling of the subarachnoid space cranial to T8, and complete myelographic block caudal to this level (Figure 2). There was no obvious heterotopic calcification seen surrounding the spinal cord (Figure 3). Given these radiographic findings, the surgical approach was altered from a thoracoscopic T6-7 discectomy to that of a posterolateral approach, facilitating intradural exploration as well as discectomy.
SURGICAL INTERVENTION The patient was positioned prone, and a T6-T8 laminectomy was performed. Intradural exploration revealed a large, compressive arachnoid cyst cranial to T8, and thick, ossified arachnoid circumferentially encasing the spinal cord, spanning the T6-T8 levels and filling the entire subdural space caudal to this level (Figure 4). The arachnoid cyst was decompressed, and a
IMAGING FINDINGS Magnetic resonance imaging (MRI) of the spine was significant for a central T6-T7 disc herniation with significant spinal cord compression. Distal to the disc herniation, the spinal cord appeared abnormally enlarged, and a syrinx was present from T6 to the conus (Figure 1A). Initially, the patient appeared to have typical spinal cord compression caused by disc herniation. On closer inspection, however, the transition from compressed to dilated cord appeared unusually abrupt, and the possibility of a dorsal intradural arachnoid cyst displacing the spinal cord anteriorly was considered (Figure 1B). Computed tomography (CT) and a CT myelogram were performed, which demonstrated again this sharp
478.e12
www.SCIENCEDIRECT.com
Figure 1. Preoperative magnetic resonance image with axial T2 (A) and sagittal T2 (B) slices.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.12.001
PEER-REVIEW SHORT REPORTS HARSHPAL SINGH ET AL.
ARACHNOIDITIS OSSIFICANS
Figure 2. Myelogram showing block at the T8 level.
central dorsal channel of the ossified arachnoid was removed in an attempt to re-establish normal cerebrospinal fluid flow caudal to T8. The entire ossification could not be removed because of the adherence of the ossification to the cord and vasculature. A right unilateral costotransversectomy was performed to gain anterior access and perform the discectomy, although at this point, under direct visualization, the disc no longer appeared to be compressing the cord. Of note, the motor evoked potential nearly doubled in amplitude after the arachnoid cyst and ossified arachnoid were removed and before discectomy. No direct drainage of the syrinx was attempted. A dural graft was sewn in place to maintain an enlarged intrathecal space, allowing for normalization of cerebrospinal fluid flow. Histological evaluation of the ossified arachnoid tissue was consistent with densely calcified lamellar bone (Figure 5).
POSTSURGICAL COURSE The patient progressively improved to independent ambulation as well as resolution of her incontinence. The syrinx also significantly improved as demonstrated by the 1-year postoperative MRI (Figure 6). However, although improved, the burning dysesthetic-type pains persist.
DISCUSSION AND CONCLUSION Incidental leptomeningeal calcifications are common. Autopsy studies reveal 6% to 76% incidence (1, 4). These are thought to be secondary to a degenerative process. Arachnoiditis ossificans, on the other hand, is present when arachnoid ossification leads to clinical symptomatology. Dense calcifi-
Figure 3. Axial (A) and sagittal (B) computed tomographic myelogram showing imaging characteristics not suggestive of arachnoid calcification.
cation and metaplastic ossification of the arachnoid is thought to be secondary to degeneration or chronic inflammation of arachnoid cell clusters. Initiating factors such as trauma, surgery, or myelography leading to arachnoiditis are postulated. A few case reports and case series describe the clinical manifestations of this process, typically myelopathy caused by thoracic spinal cord compression/ischemia, or cauda equina syndrome caused by lower lumbar ossification (3, 6). Two previous case reports describe the development of syringomyelia secondary to arachnoiditis ossificans (3, 5). In one of these, an arachnoid cyst also developed, and was thought to be a significant contributor to the clinical deterioration. A spiral CT scan is thought to be the optimal radiographic study for demonstrating the ossified arachnoid plaques. In this report, we present the case of a woman who developed a rapidly progressive thoracic myelopathy, localizable to the mid-thoracic spine. A T6-T7 central disc herniation with significant anterior spinal cord compression was identified on MRI imaging. This was adequate to explain the myelopathy and syringomyelia, and thus no preoperative, nonmyelographic CT scan was performed. However, both MRI and CT myelogram did suggest a superimposed anterior displacement of the spinal cord, presumably from an arachnoid cyst, and thus intradural exploration was undertaken, leading to the diagnosis. This report is significant for several reasons. The first is the illustration of the coexistence of multiple anatomic abnormalities at the same spinal levels. The initial diagno-
WORLD NEUROSURGERY 76 [5]: 478.e12-478.e14, NOVEMBER 2011
sis of disc herniation might have led to a lateral surgical approach via thoracotomy. This procedure would not have addressed the patient’s true pathology, and might have been dangerous in the presence of the cyst and ossifications. Once the cyst had been decompressed, and a channel established through the ossification, the motor potentials doubled in amplitude and the anterior disc was visualized to no longer have a compressive component. Although the pathologic evaluation demonstrated mature lamellar bone, it is noteworthy that the CT scan did not demonstrate dense circumferential calcification around the spinal cord. Previous reports have stated that the most reliable diagnostic test for arachnoiditis ossificans is noncontrast CT (2). This case demonstrates that the diagnosis cannot be excluded entirely based on a CT scan. Although the vast majority of arachnoid calcifications are not clinically significant,
Figure 4. Intraoperative image showing calcified arachnoid held by forceps with exposed spinal cord underneath.
www.WORLDNEUROSURGERY.org
478.e13
PEER-REVIEW SHORT REPORTS HARSHPAL SINGH ET AL.
ARACHNOIDITIS OSSIFICANS
Figure 5. Hematoxylin and eosin stain (original magnification ⫻5) showing densely calcified lamellar bone.
the term arachnoiditis ossificans implies clinical deterioration caused by these plaques. There has been some discussion with respect to the underlying cause of the deterioration. It is typically thought to be secondary to direct spinal cord compression caused by the space-filling mass. Resection of the mass is usually attempted, with mixed or poor results. This is likely because of the adherence of the ossification to the substance of the cord itself, requiring significant intraoperative manipulation in often unsuccessful attempts to remove it. In
this case, although there was a very large circumferential mass of bone lining the cord, marsupialization of the arachnoid cyst alone was adequate to cause a doubling in the amplitude of the motor evoked potential. The patient clinically improved despite a partial resection of the mass. This suggests that direct compression caused by the calcifications may not be the primary cause of the myelopathy. The altered cerebrospinal fluid dynamics secondary to the obstruction in subarachnoid flow may predispose to the formation of an arachnoid cyst,
and the cyst itself may be the proximate cause of the myelopathy. Drainage of the cyst leads to rapid decompression of the spinal cord, whereas reestablishing cerebrospinal fluid flow by creating the channel may help to prevent recurrence of the cyst. In the 2 earlier reports in patients with arachnoiditis ossificans and syringomyelia, the syrinx was directly drained at the time of surgery. In this case, the syrinx was presumed to be secondary to altered flow, with direct compression from the arachnoid cyst leading to ischemic changes. Therefore, it was not directly drained, and was itself treated by reestablishing normalized subarachnoid flow. The decreasing postoperative size of the syrinx supports this course of action. Arachnoiditis ossificans remains a rare cause of myelopathy in patients. Unfortunately, the clinical outcomes after surgery have been quite disappointing. A greater understanding of the dynamics leading to the clinical presentation may help direct treatment for these patients.
REFERENCES 1. Herren RY: Occurrence and distribution of calcified plaques in the spinal arachnoid in man. Arch Neurol Psychiatry 41:1180-1186, 1939. 2. Jaspan T, Preston BJ, Mulholland RC, Webb JK: The CT appearances of arachnoiditis ossificans. Spine 15: 148-151, 1990. 3. Kahler RJ, Knuckey NW, Davis S: Arachnoiditis ossificans and syringomyelia: a unique case report. J Clin Neurosci 7:66-68, 2000. 4. Morrison RL, Cob S, Bauer W: The effect of advancing age upon the human spinal cord. Boston: Harvard University Press; 1959:40-41. 5. Nagpal RD, Gokhale SD, Parikh VR: Ossification of spinal arachnoid with unrelated syringomyelia. J Neurosurg 42:222-225, 1975. 6. Papavlasopoulos F, Stranjalis G, Kouyialis AT, Korfias S, Sakas D: Arachnoiditis ossificans with progressive syringomyelia and spinal arachnoid cyst. J Clin Neurosci 14:572-576, 2007. Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. received 07 June 2010; accepted 01 December 2010 Citation: World Neurosurg. (2011) 76, 5:478.e12-478.e14. DOI: 10.1016/j.wneu.2010.12.001 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
Figure 6. One-year postoperative axial (A) and sagittal (B) magnetic resonance images showing reduction in syrinx size.
478.e14
www.SCIENCEDIRECT.com
1878-8750/$ - see front matter © 2011 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2010.12.001