CES is a is a well-known but rare and poorly understood complication of AS. This complication may cause numbness and/or tingling in the buttocks and lower extremities, weakness in the legs, and incontinence of bladder and/or bowels. CES manifests late in the course of AS, often at a time when the AS is no longer active[6]. The time interval between the onset of AS and the clinical manifestation of CES averages 35 years (range 17–53 years) [7]. MRI characteristically shows an enlarged caudal thecal sac, bone erosion and dural ectasia[3]. The lesions primarily affect the lumbar region but can also appear in the thoracic region[8].
Previous studies have revealed that the formation of dural ectasia and arachnoid diverticulum in AS is closely related to the chronic inflammatory process[9]. Liu et al. [10] described fibrous tissue with scant lymphoplasma cell infiltration in the dura mater of an AS patient with dural ectasia. Local inflammation leads to a slowly progressive process of bony erosion[11, 12]. Furthermore, dural fibrosis causes diminished resorption of cerebrospinal fluid (CSF). Reduced elasticity and compliance of the caudal sac exposed to inflammatory changes is also a factor inducing dural sac enlargement and diverticula formation[13].
The direction of arachnoid diverticula formation is thought to be dependent on the direction of the force of increased CSF pulse pressure and the “give” of the structures surrounding the spinal canal[6]. Dural ectasia is more likely to occur in the posterior elements rather than the vertebral bodies [4, 5]. Posterior dural ectasis in AS was first documented using myelography by Hauge[14], and has been well described subsequently. However, the cases with anterior dural ectasis are more rare (Table 1) [6,11,15−18]. These changes seem to occur commonly at the level of the thoracolumbar junction and upper lumbar vertebrae[17].
Table 1
Summary of the previous case reports of anterior dural ectasia assciated with CES in AS
Author | Age (y) | Sex | Time since onset of CES (years) | Presenting complaints | Investigation | Lesion site | Description of the lesion | Neural tissue herniation |
Byrne et al. (1985)[15] | 71 | Male | 2 | Difficulty walking, impotence, bladder disturbance | Myelography | L2-L3 | Intradural cyst (believed to be arachnoid cyst) | Yes |
Ginsburg et al. (1997)[6] | 65 | Male | 9 | Numbness and weakness in both legs, right buttock and posterior thigh pain, bladder and bowel disturbance, impotence | MRI | T12–L1 | Arachnoid diverticula | Yes |
Baur et al.(1997)[16] | 50 | Male | 2 | Numbness in left buttock and feet, bladder disturbance, faecal incontinence | CT, CTM, MRI | T12–L1 | Ventral dural defect | Yes |
Hayashi et al. (2009)[17] | 63 | Male | 2 | Numbness and tingling left leg posteriorly, difficulty walking, constipation | MRI | L1-L2 | Arachnoid diverticula | No |
Bele et al. (2011)[11] | 50 | Male | 0.5 | Weakness of right leg | CT, MRI, MRM | L1-L2 | Arachnoid diverticula | Yes |
Huang et al. (2019)[18] | 44 | Male | 0.1 | Numbness and weakness of left leg | CT, MRI, contrast-enhanced MRI | L1-L2 | Arachnoid diverticula | Yes |
Present case | 78 | Male | 1 | Weakness of left leg | CT、MRI | T12-L1 | Arachnoid diverticula | Yes |
CTM = CT myelography; MRM = magnetic resonance myelogram |
Dural ectasia can also be caused by spinal tumor, Marfan syndrome, Ehlers-Danlos syndrome, or neurofibromatosis, but the patient’s clinical manifestations and imaging findings did not support the diagnosis of these disease. In our case, anterior dural ectasia and bony erosion of the posterior aspect of T12 and L1 vertebral bodies were seen. MRI also demonstrated ventral shift and adhesion of the conus medullaris and the cauda equine. It is a remarkable fact that our patient presented with weakness of the left leg, but without bladder and rectal dysfunction. The mechanisms of nerve root damage are poorly understood, but some hypotheses have been proposed. These include inflammatory injury from arachnoiditis, gravitational traction injury resulting from the compression of arachnoid diverticula, and traumatic damage from excessive CSF pressure fluctuations [7, 19, 20].
There is currently no standard and uniform treatment for dural ectasia associated with CES in AS. Kotil et al.[21] recommend that asymptomatic or symptomatic patients with dural ectasia should be closely observed without need for immediate surgical intervention. Ahn et al. [22]suggested that steroids are ineffective for patients with CES in AS, whereas non-steroidal anti-inflammatory drugs may improve back pain but do not improve neurological deficits, probably because no active inflammation occurs in the chronic stage. Huang et al.[18] reported a case of anterior dural ectasia with AS, and treated with an oral nonsteroidal anti-inflammatory drug. Neurological deficits remained stable during 2 years of follow-up, consistent with the disappearance of the dural enhancement in the lytic lesion of the vertebral bodies. Their case supports the essential role of inflammation in anterior dural ectasia formation and confirms the effectiveness of anti-inflammatory therapy. Infliximab is a humanized antibody against tumor necrosis factor α (TNF-α) that is used in the treatment of active AS. Cornec et al.[23] reported on an AS patient with posterior dural ectasia that was unexpectedly cured by treatment with Infliximab, and subsequent studies have confirmed this dramatic finding[9, 10].
A meta-analysis by Ahn et al. [22] concluded that surgical treatment of dural ectasia with CES might improve the neurologic symptoms or halt the progression of neurologic deficit, and has a better outcome than conservative or no treatment. However, the literature regarding management of anterior dural ectasia is scarce. Surgical options for dural ectasia with CES include detethering of the cord, decompressive laminectomy, and lumboperitoneal shunting (LPS). Liu et al.[10] found that little improvement was achieved after performing de-adhesion of the tethered conus medullaris. Bele et al.[11] suggested releasing the arachnoid adhesions and fibrosis around the cauda equina roots, which may lead to deterioration of neurological function. Decompressive laminectomy provides more space for the neural elements at the cauda equine, but LPS for CES in AS is more efficient than laminectomy[24]. LPS helps in relieving the intradural pressure and has been offered for the more common posterior dural ectasia with CES[24]. Ea et al. [13] reported that five AS patients with dural sac dilation achieved substantial improvement that persisted at follow-up by treatment of LPS. Although it is not clear whether LPS is effective for anterior dural ectasia, Bele et al.[11] suggested performing LPS, as the pathogenesis for an anterior and posterior dural ectasia remains the same.