Meningocele Manqué Discovered During Filum Terminale Resection in Occult Tethered Cord Syndrome.

Background: Meningocele manqué (MM) is characterized by tethering of the spinal cord, nerve roots, or filum terminale by fibrous attachments formed by atrophic or incomplete meningoceles. Patients with MM can present with symptoms of tethered cord syndrome (TCS).
Case Description: We present the case of an MM discovered incidentally during microsurgical resection of filum terminale for occult TCS. The MM was not visible on the preoperative magnetic resonance imaging (MRI) studies. After L2-L3 laminotomy, an extradural mass was appreciated adherent to the spinal dura, which was found to be an MM. The nerve roots of the cauda equina were found to protrude through the dura, consistent with tethered cauda equina. After microsurgical resection of the filum terminale, the tethered cauda nerve roots were stimulated, and redundant electromyographic signals were detected at both the left- and the right-sided muscles of the lower extremities. Microsurgical repair of the MM was performed, assuming that the patient's symptoms of TCS would also be explained by the MM and that her symptoms would likely have been incompletely addressed by filum terminale release alone. A review of the preoperative 3-dimensional constructive interference in steady state MRI sequence revealed pathological features at the L2-L3 level suspicious for our intraoperative findings of an MM.
Conclusions: Surgeons planning filum terminale release for occult TCS should always be aware of the possibility of associated pathological features of tethering that might be overlooked. In retrospect, the detection of MM was enabled by the high-resolution 3-dimensional constructive interference in steady state MRI sequence. This finding advocates for the use of high-resolution MRI for patients undergoing evaluation for occult TCS to detect pathological features that might otherwise be undetected.
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