Re-evaluation of the dinosaur tail sign: Analysis of spinal magnetic resonance imaging signs in patients with chronic post-dural-puncture headache.

Abstract

Objective: This study aimed to assess magnetic resonance imaging (MRI) findings of the lumbar spine in patients with chronic post-dural-puncture headache.

Background: Post-dural-puncture headache is a common complication after dural puncture usually resolving within 14 days. However, a chronic course (>14 days persistence) is increasingly being recognized and may lead to tremendous symptom burden. While current research shows that MRI of the head is mostly unremarkable in chronic post-dural-puncture headache, lumbar imaging signs have not yet been systematically studied.

Methods: This is a retrospective, single-center diagnostic case-control study. We identified all patients between 09/2022 and 12/2024 at the University Hospital Freiburg, Germany, with chronic post-dural-puncture headache (defined as persisting symptoms for >14 days post puncture or after ≥1 epidural blood patch), and recruited 30 healthy controls between 10/2024 and 07/2025 without prior history of intentional or unintentional lumbar puncture, all undergoing 3D high-resolution heavily T2-weighted lumbar MRI (at 0.63 mm spatial resolution). The "dinosaur tail sign" (interspinous arched T2w-hyperintensities) was assessed as originally published, recording numbers of involved spinal levels, while its appearance was subjectively graded as subtle, moderate, or prominent. Moreover, presence of arachnoid blebs and lumbar extradural fluid were recorded. Evaluation was independent and blinded; discrepancies were resolved by consensus. In a subgroup of patients with T1-weighted contrast-enhanced lumbar spine imaging (51/54), suspicious enhancement, which potentially may be attributable to the puncture, was analyzed, while none of the controls received contrast enhanced spinal MRI.

Results: The final cohort resulted in 54 patients with chronic post-dural-puncture headache with 44 females (81%) and a mean age of 38.2 years (SD ±9.8). The dinosaur tail sign was present in 27/54 patients (50%) and 21/30 controls (70%), with a numerically higher frequency in controls (70% vs. 50%, odds ratio [OR] 2.31, 95% confidence interval [CI] 0.83-6.84, p = 0.107, p-adjusted = 0.240). The sign appeared at a median of two levels in both groups (interquartile range [IQR] 2.0-4.0 for patients vs. 1.0-3.0 for controls). Visual impression of the sign was graded subtle in 15 patients vs. 15 controls, moderate in nine vs. six, and prominent in three (two of three with extradural fluid) vs. none (p = 0.321, p-adjusted = 0.432 for all groups). Lumbar extradural fluid was observed in 4/54 patients (7%), arachnoid blebs in 10/54 patients (19%; 9% definite, 9% suspicious), with one patient presenting with two suspected blebs. Neither extradural fluid nor arachnoid blebs were found in any controls. Overall, noticeable contrast enhancement in the lumbar spine was found in 17/51 patients (33%).

Conclusion: The dinosaur tail sign, originally described in patients with acute post-dural-puncture headache (≤14 days persistence), was unable to reliably distinguish patients with chronic post-dural-puncture headache from healthy controls. Other findings, such as arachnoid blebs or extradural fluid collections, were only present in chronic post-dural-puncture headache, but rare. Contrast enhancement in the lumbar spine was found in approximately one third of patients but was mostly attributed to nonspecific findings. Further spinal MRI signs need to be identified to enable diagnosis of chronic post-dural-puncture headache in the future.