Trigeminal neuralgia (TN) is known as the most serious pain in the world. Intense and recurring pain in the sensory distribution of the trigeminal nerve in the face and surgery are the main treatments for severe patients[1]. The prevalence of the disease varies in different regions, with an average of 12 to 29 people per 100,000 people globally and as high as 56 people per 100,000 people according to a survey of six major cities in China. TN greatly affects patients’ quality of life and often leads to emotional disorders and physical health problems [2–4].
Theoretically, TN can be divided into classic types if vascular is found on the trigeminus, and immediate analgesia can be expected after vascular decompression surgery[5]. Bendtsen reported on 5149 patients with classic TN who underwent microvascular decompression (MVD) surgery and were followed for 3 to 11 years; the authors found that the pain cure rate reached 62 to 89% [6, 7]. Alternatively, if there is no vascular compression upon any part of the trigeminus, TN is usually classified as [8–10], and internal neurolysis (IN) surgery is usually performed with satisfactory treatment efficacy. Internal neurolysis (IN) involves longitudinal incision of the intracranial nerve root to achieve nerve micro destruction and is highly effective at curing ITN and significantly reducing the incidence of facial sensory disorders and the degree of numbness [11, 12]; therefore, IN has been gradually accepted by an increasing number of scholars [13–15]. Our research team also used IN to treat ITN and came to similar conclusions [16]. The different characteristics and treatment choices of these diseases are due to their different pathophysiological bases and pathogenesis. At present, the pathophysiological basis of CTN is generally believed to be related mainly to the pressure of blood vessels on the intracranial segment of the trigeminal nerve, which leads to secondary demyelination of the nerve, resulting in abnormal and oversensitive nerve transmission through the production of “ignition”, “short circuit”, “sympathetic nerve excitation” and other effects, thus causing pain attacks [1, 5]. In contrast, the pathophysiological basis and pathogenesis of the ITN are not fully understood and may involve changes in neurons and synapses as well as the involvement of inflammatory and immune responses, among other factors.
However, the truth is not simple in clinical practice (i.e., severe vascular compression or no vascular space). Clinicians are usually puzzled when they find slight vascular contact because this contact seems unlikely to cause secondary demyelination of the nerve, and a second IN surgery would be inevitable if MVD surgery failed. This condition looks like CTN, but in fact, the blood vessels are most likely just an illusion (“vascular illusion”) and are actually the ITN. It looks like a dilemma. If IN surgery is performed directly, this may mean unnecessary nerve damage, and any nerve damage has its own side effects, such as numbness and chewing dysfunction [16, 17]. If vascular decompression is used, this may mean that the operation fails and a second operation is needed, which is also an injury.
It is difficult to accurately distinguish between the ITN and CTN because of this slight vascular contact with currently available preoperative neuroimaging methods. Therefore, surgical procedures are often performed without any reference but rather according to the doctor’s experience, which may lead to ineffective or unnecessary iatrogenic damage after surgery. In fact, single vascular decompression surgery is usually ineffective, and to avoid the need for a second operation due to ineffective decompression and to improve the success rate of the first operation, IN surgery alone [13] or combined with vascular decompression [15] is often used in clinical treatment. This is clearly due to a lack of helplessness, and more precise methods need to be further developed. Therefore, it is important to establish a novel preoperative predictive evaluation method to accurately distinguish TN patients who have slight vascular contact with the CTN from those with slight vascular contact with the ITN with “vascular illusion”. This approach would be quite helpful in improving the cure rate while ensuring the reduction of iatrogenic injury.
To address this, we need clearly labeled training data, including a group of patients who have been clearly defined as CTN and ITN, as well as poorly classified data (i.e., those with “vascular illusion”). However, as mentioned above, to improve the first success rate and to avoid a second surgery, in previous clinical work, these patients were almost exclusively treated with IN surgery because IN is a kind of radiculotomy. This approach undoubtedly hides a subset of CTN conditions, leaving these patients unlabeled.
To solve this problem, a two-step scheme might be used, and the present study is the first step of the whole process. Here, preoperative MR images that were clearly labeled CTN and ITN were collected to construct a classification model. This approach allows us to reclassify poorly classified patients who have undergone IN, although training data for this poorly classified patient population are lacking in this model. Furthermore, the model provides us with a reference for choosing a relatively more appropriate surgical paradigm for poorly classified surgical candidates. In the future, second, poorly classified patients were labeled “classic” if MVD surgery was successful or “idiopathic” if MVD surgery failed according to the model instructions. Afterwards, as these poorly classified patients were labeled and added to the training dataset of the model, we could constantly improve the model’s classification accuracy.