In 1924, Frazier and Russell et al. [7] first described a pain syndrome distributed along the trigeminal nerve. The type of pain described is not typical of craniocerebral neuralgia, which mainly manifest as unilateral persistent severe burning or crushing facial pain, without autonomic neurosis, and the imaging examination being also negative. Initially, this pain syndrome was considered to be atypical trigeminal neuralgia. Its pain area is similar to trigeminal neuralgia with indistinct location and often unilateral onset. In contgrast to trigeminal neuralgia, it is characterized by persistent facial pain, which is often related to the patient's mood. At present, this pain syndrome is termed atypical facial pain (AFP) or persistent idiopathic facial pain (PIFP).
The pathological mechanism behind the pain is uncertain. Some studies believe that it may be caused by the over-activity of the central nerve secondary to the injury of the primary afferent nerve[3, 6]. In addition, it may also be caused by the combined effect of physiological and psychological factors [3, 6, 8]. The pain should also be differentiated from other causes of facial pain such as trigeminal neuralgia, cervical headache, temporomandibular joint disorder, sphenopalatine neuralgia, rhino-ciliary neuralgia, sinusitis, head and neck tumors and intracranial space-occupying lesions, migraine headache, cluster headache etc [9–12]. Conventional conservative treatments such as tricyclic antidepressants or anticonvulsants are often used in clinic, but the curative effect is uncertain. As reported in previous studies,, trigeminal ganglion and its branch block, sphenopalatine ganglion block and stellate ganglion block may have a certain effect on this condition [13–15].
As the largest parasympathetic ganglion in the head and neck region, sphenopalatine ganglion (SPG) is located in the pterygopalatine fossa of the lateral wall of the nasal cavity at the level of the middle turbinate. It receives three nerve roots. The sensory root from the maxillary branch of the trigeminal nerve, the parasympathetic root derived from the superior salivatory nucleus (SSN)which travel in the nervus intermedius, a part of the facial nerve, forming the greater petrosal nerve, and the sympathetic root arises from superior cervical ganglion, travelling through the internal carotid plexus and then the deep petrosal nerve, which joins with the greater petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve) before entering the SPG.. The ganglion sends out many branches, which are distributed in the orbit, lacrimal gland, nasal cavity, pharynx, maxillary sinus, hard palate, soft palate and upper alveolar in the mouth, whose function include the general sensation, gland secretion and innervation to small blood vessel. Due to the complexity of its anatomical location, SPG plays an important role in various head and face pain syndromes, including trigeminal neuralgia and sphenopalatine neuralgia, atypical facial pain, vasomotor rhinitis, eye diseases and herpes infection. Clinical trials have shown that these diseases can be effectively treated by sphenopalatine ganglion block (SPGB) [16, 17, 18]. In this study, sphenopalatine ganglion block combined with ozone injection through pterygopalatine fossa under CT guidance has achieved remarkable results, and the curative effect is significant compared with the control group. The analgesic mechanism of percutaneous ozone injection is still unclear, which may include [19]: (1) increased local oxygen concentration and stimulating the expression of antioxidant enzymes resulting in an increased production of superoxide dismutase (SOD) which reduce the effect of reactive oxygen species (ROS) to cells; (2) inhibit the release of anti-inflammatory factors, cause vasodilation, improve oedema around nerves; (3) inhibit the synthesis and release of prostaglandins, bradykinins and pain causing factors; and (4) neutralize interleukin soluble receptors, such as IL-1, IL-2, IL-8, IL-12, etc. In addition, studies have found that ozone can directly act on nerve endings and stimulate inhibitory interneurons to release substances such as cerebrospinal peptide to achieve analgesic effect [19, 20]. At the same time, after local injection of ozone, it stimulates local tissues to produce acupuncture like curative effect, so as to produce endogenous analgesic substances in the body and relieve pain [21]. Besides, some research also showed that ozone may promote the recovery of nerve demyelination changes but needs long-term research to further prove this point[19]. And, when ozone is injected, due to the effect of pressure, it can achieve the effect of releasing adhesion and relieving nerve compression.
In this study, ozone combined with sphenopalatine ganglion block was used to treat atypical facial pain. After follow-up for 1 week, 2 weeks, 1 month, 3 months and 6 months, the VAS score and PSQI score of patients were significantly lower than those before treatment, and the difference was statistically significant. Compared with simple nerve block, the VAS score and PSQI score of the experimental group were lower, suggesting that transpterygopalatine fossa ozone combined with sphenopalatine ganglion block has a better therapeutic effect on atypical facial pain. Traditional sphenopalatine ganglion block is mostly identified and approached according to body surface markers, while the pterygopalatine fossa is deep and the space is narrow. So a blind puncture can lead to a high incidence of adverse reactions with the therapeutic effect being far from ideal. In this study, multi-slice spiral CT guided localization and infiltration, combined with multiplanar reconstruction technology, improved the accuracy and safety of procedure. Most patients in the experimental group had different degrees of flatulence and pain discomfort at the procedure area after a short period of time. This may be related to the diffusion of ozone at the site of infiltration area and surrounding tissues. The above flatulence and pain symptoms basically disappeared after observation for 1–3 days. There were no serious complications such as intracranial infection and bleeding in both groups, indicating that CT guided transpterygopalatine fossa ozone combined with sphenopalatine ganglion block is safe in the treatment of atypical facial pain.