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Electron Microscopy of Dural and Arachnoid Disruptions After Subarachnoid Block
Miguel Angel Reina1, Anna Puigdellívol-Sánchez, Stephen P Gatt
1From the *Department of Clinical Medical Sciences, CEU San Pablo University School of Medicine; and †Department of Anesthesiology, Madrid-Montepríncipe University Hospital, Madrid; ‡Laboratory of Surgical NeuroAnatomy, Human Anatomy and Embryology Unit, Faculty of Medicine, Universitat de Barcelona, Barcelona; and §Antón Borja Primary Care Centre, Terrassa Health Consortium, Rubí, Spain; ∥Department of Anesthesia, Royal Hospital for Women & Prince of Wales & Sydney Children's Hospitals, Randwick & University of New South Wales, Kensington, Sydney, New South Wales, Australia; **Department of Anesthesia Critical care and Pain Management, General University Hospital, Valencia and Department of Surgical Specialties, School of Medicine, Valencia University, Valencia; and ††Laboratory of Surgical NeuroAnatomy, Human Anatomy and Embryology Unit, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain; and ‡‡Department of Anesthesiology & Perioperative Medicine, The University of Queensland & Royal Brisbane & Women's Hospital, Brisbane, Queensland, Australia.
Background:
It has been customary to attribute postdural puncture headache (PDPH) incidence and severity to size and nature of the dural hole produced during major neuraxial blockade or diagnostic dural puncture. Needle orientation in relation to the direction of dural fibers was thought to be of importance because of the propensity for horizontal bevel placement to cause cutting rather than splitting of the dural fibers.
Methods:
In vitro punctures of stringently quality-controlled human dural sac specimens were obtained with 27-gauge (27G) Whitacre needle (n = 33), with 29G Quincke used parallel to the spinal axis (n = 30), and with 29G Quincke in perpendicular approach (n = 40). The samples were studied with a scanning electron microscope, and the perimeter, appearance, and area (%) of the lesion were calculated.
Results:
When using small 27G to 29G needles, neither needle tip characteristics nor needle orientation had a substantial bearing on the damage to dural fibers in the dural lesion. Of ultimate importance was the characteristic and size of the hole in the arachnoid. Arachnoid layer lesions produced by different types of spinal needles were not markedly different.
Conclusions:
Accepted theories of the etiology of PDPH need to be revised. This article marks the first time that arachnoid layer damage has been quantified. Dural fibers tend to have sufficient "memory" to close back the hole created by a spinal needle, whereas arachnoid has diminished capacity to do so. The pathogenesis of PDPH and its resolution algorithm are a far more complex process that involves many more "stages" of development than hitherto imagined.
