Low tension of the dural sac as a cause of unsuccessful myelography in spontaneous intracranial hypotension: Evidence from computed tomographic-guided myelography
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.227307
Source of Support: None, Conflict of Interest: None
Spontaneous intracranial hypotension (SIH) is an uncommon disorder characterized by orthostatic headaches, low cerebrospinal fluid (CSF) pressure, and diffuse pachymeningeal gadolinium enhancement on magnetic resonance (MR) imaging. Spontaneous spinal CSF leaks along the spinal nerve roots or defects in the dural matter are recognized as the underlining pathogenic mechanisms of SIH., Demonstration and localization of spinal nerve root abnormalities, dural defects, or CSF leakage are essential to provide a definitive diagnosis, as well as to serve as a guide for therapeutic interventions., Computed tomography myelography (CTM) and gadolinium-enhanced MR myelography (Gd-MRM) are reliable imaging modalities commonly used for detecting spinal CSF leakage.,
A successful CTM or Gd-MRM requires correct needle placement in the subarachnoid space (dural sac) and injection of an appropriate amount of contrast medium. Accidental injection of contrast medium into the epidural or subdural space has been reported to occur in 1.9% of the patients undergoing a CTM procedure. Failure of CTM or Gd-MRM is more common in patients with SIH. Between January 2012 and October 2013, 3 patients who underwent failure of myelography had CTMs performed under CT guidance due to their deteriorating condition and the necessity of detecting CSF leakage in them. In this letter, the CT images and procedures utilized in these 3 cases are retrospectively reviewed, and some reasons for the unsuccessful myelography in patients with SIH are discussed.
A 39-year old man who had experienced a failed CTM and Gd-MRM, underwent a CT-guided CTM on day 22 after the headache onset. He provided a signed informed consent prior to the examination. The CT-guided lumbar puncture was performed though the L3/4 spinal interspace by an experienced neurologist who used a 20-guage spinal needle. The location and orientation of the needle were adjusted based on the CT images. CSF was seen eluting from the needle, and the CSF pressure was measured as 60 mmH2O. However, the dural sac was observed to be completely shriveled under the pressure, even when the needle tip almost touched the posterior edge of the lumbar spinal canal. A total of 1–2 mL of the nonionic iodinated contrast medium (10 mL) iohexol, premixed with 10 mL of preservative-free 0.9% saline was injected to confirm the placement of the needle tip within the dural sac. However, the contrast was shown mainly in the epidural space behind the deformed dural sac [Figure 1]a and [Figure 1]b; therefore, the next phase of the examination was abandoned.
A 33-year old man who suffered from several acute episodes of severe orthostatic headaches was admitted for the placement of targeted epidural blood patch (EBP). On day 45 after the headache onset, he experienced a failed CTM because CSF was not seen eluting from the needle during the puncture (so called “dry tap”). The patient underwent a CT-guided CTM on the next day. CSF drops could not be observed throughout the procedure. CT images showed that the needle tip was contacting the posterior wall of the dural sac, but was unable to penetrate the dura because the dura was focally indented by the pressure of the needle. Consequently, application of a greater pressure merely deepened the indentation. After injecting a few drops of contrast media through the needle, accumulation of contrast media was observed immediately behind the deformed “petal-like” dural sac [Figure 2]a and [Figure 2]b.
A 25-year old woman who had failed to complete an earlier CTM due to “dry tap” underwent a CT-guided CTM which proved to be successful. CT imaging showed focal indentation of the dura under the needle tip at the beginning of the operation [Figure 3]a and [Figure 3]b. After making several adjustments related to the depth and angle of the needle, we finally penetrated the dura and confirmed the correct location of the needle tip [Figure 3]c and [Figure 3]d. Following such a confirmation, 15 mL of diluted nonionic iodinated contrast solution was injected into the dural sac, and the subsequent CTM was conducted from the upper cervical to the lower lumbar spine, with the images being of 0.75 mm minimum axial section thickness.
Myelography is a common examination performed in neurological clinics; it is unsuccessful in 1.9% of all patients who undergo the procedure. However, some researchers have found that lumbar punctures can be challenging in SIH patients. They suspected that it was caused by a collapsed dural sac. In our study, all the three cases showed a focal dural sac indentation at the tip of the needle, and in two cases, the needle failed to penetrate the dura, even with CT guidance. We believe that the low tension and collapse of the dural sac, rather than technical factors, such as patient positioning and depth or angle of puncture, were the primary reasons for the unsuccessful myelography in patients with SIH.
An occasional “dry tap” in SIH patients has been previously mentioned in the literature., In our three cases, a “dry tap” occurred in two cases, even when we applied a negative pressure suction using a syringe. Based on our observations after studying the CT-guided CTM images, we propose that a “dry tap” can be caused not only by a complete lack of CSF pressure but also by incorrect location of the needle tip.
This study demonstrates that, while CT-guided CTM can enable better observation of the needle positioning, as well as a real-time observation of the shape of the dural sac during the lumbar puncture procedure, an unsuccessful myelography may still occur. A low CSF pressure and collapse of the dural sac are responsible for unsuccessful myelography in patients with SIH. We suggest MR hydrography of the spine as an alternative procedure for patients with SIH who have experienced a failed myelography.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that name and initial will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3]