Bilateral transnasal sphenopalatine block for treating postdural puncture headache.

We read the review article by Kwak [1] about postdural puncture headache (PDPH) with great interest. The author has reviewed the literature and has very thoroughly discussed the diagnosis, risk factors, pathophysiology, prevention, and treatment of PDPH. In this letter, we want to mention another simple technique that can be performed at the bedside or in the outpatient department and is effective at relieving PDPH. The procedure is known as transnasal bilateral sphenopalatine ganglion block. In a review article published in the Korean Journal of Pain, we have reviewed the evidence for the efficacy of bilateral, transnasal sphenopalatine ganglion block at relieving PDPH [2]. The sphenopalatine ganglion (SPG), which is also known as the pterygopalatine ganglion, Meckel's ganglion, or the nasal ganglion, is a triangular parasympathetic ganglion located superficially in the pterygopalatine fossa, posterior to the middle nasal turbinate and anterior to the pterygoid canal. It measures 5 mm in size with a 1 to 1.5 mm layer of connective tissue and mucous membrane surrounding the ganglion. Although essentially a parasympathetic ganglion, the SPG is a junction that has sympathetic, parasympathetic, and sensory innervation overlapping in a small area [3]. This is why postganglionic parasympathetic and sympathetic neurons and the somatic sensory afferents can all be blocked by an SPG block. Therefore, an SPG block is indicated in a variety of acute and chronic head and neck pain syndromes of varying etiologies, such as trigeminal neuralgia, complex regional pain syndrome I and II, temporomandibular joint pain, postherpetic neuralgia, cluster headaches, Sluder's neuralgia, paroxysmal hemicranial pain, head and neck cancer pain, vasomotor rhinitis, atypical facial pain, and postoperative analgesia after head and neck cancer surgery [4].

Chronic pain physicians perform the SPG block via transnasal, transoral, subzygomatic, and lateral infratemporal approaches using radio-opaque contrast and a fluoroscope. These approaches are not only cumbersome but also require sufficient training to perform safely and accurately. However, the transnasal SPG block is very simple and does not need contrast or a fluoroscope. With the patient in the supine position and the neck extended, a sterile swab-stick soaked with lidocaine solution is inserted through the nostril after adequate lubrication until resistance is encountered. The resistance is due to the posterior pharyngeal wall, which is superior to the middle turbinate. The swab needs to be left there for 10??5 min. The procedure is repeated in the other nostril. The mucous membrane covering the SPG facilitates drug penetration into the ganglion after topical application or infiltration (Fig. 1).

Fig. 1

The image shows the location of the sphenopalatine ganglion and the path traversed by the swab-stick when inserted through the nostril (Adapted from Nair and Rayani. Korean J Pain 2017; 30: 93-7).

In PDPH, there is continuous cerebrospinal fluid (CSF) loss, which leads to decreased intracranial volume. The intracranial volume is restored by compensatory vasodilation mediated by parasympathetic activity, which, along with traction on the painsensitive intracranial structures, leads to a throbbing headache. Even after the restoration of the intracranial volume after vasodilation, the parasympathetic activity continues. SPG block inhibits this parasympathetic activity, which inhibits vasodilation [5]. This relieves PDPH. The block can be repeated the next day if the pain relief is not complete. However, as the SPG block does not address the CSF leak, other supportive measures need to be continued for a few days until complete pain relief is achieved; these include bed rest, analgesics (acetaminophen or non-steroidal anti-inflammatory drugs), hydration, and laxatives.

An epidural blood patch (EBP) is considered the gold standard for managing moderate to severe PDPH. However, it is an invasive procedure. There is always the possibility of another inadvertent dural puncture while performing an EBP. When an EBP does not provide complete pain relief, it has to be repeated. Unwanted complications have also occurred after an autologous EBP, such as meningitis, arachnoiditis, seizures, loss of hearing and vision, radicular pain, and neural deficits. These are the issues that have to be addressed while planning an EBP. However, if the CSF leak continues and the patient does not get complete pain relief after a few sessions of SPG block, an EBP can be considered.

In conclusion, a bilateral transnasal SPG block is a simple, effective, minimally invasive way to manage moderate PDPH, along with other supportive measures.