Combined HDS is a rare condition that can possibly affect one or both sides either synchronously or metachronously. In 1998, Kobata et al. first described that combined HDS accounted for 2.8% of all patients with HDS and is accelerated by aging and hypertension [1]. Further, some recent studies have similarly revealed that combined HDS is present in approximately 3% of patients with HDS, and the mean age of patients with combined HDS was significantly higher than that of those with single HDS [2, 3]. To date, no study has reported on its development before 20 years of age. To the best of our knowledge, only case series and case reports of single HDS have been published in pediatric and adolescent populations [8,9,10,11,12,13,14,15,16]. In the present report, we present an extremely rare case of combined HDS in an adolescent patient.
HDS has been rarely mentioned in pediatric textbooks. In addition, the data from studies among the pediatric population reporting on TN and GPN suggested a high proportion of venous compression compared with adults, which might cause an atypical clinical presentation (e.g., pain that occurs while lying down at night) [10, 12]. Therefore, HDS in the young population is likely to cause a missed diagnosis or delayed appropriate treatment.
CISS MRI provides remarkable contrast between the cranial nerves, small vessels, and cerebrospinal fluid in the REZ; therefore, it is definitely useful in diagnosing HDS. Most cases of TN or GPN alone are usually caused by neurovascular compression at the REZ by meandering vessels. The most common offending vessels are the SCA, involving about 50% of TN cases, and the PICA in GPN, which are also responsible for cases of combined HDS [4,5,6,7]. However, not all cases of neurovascular compression are clinically symptomatic. Anatomical findings related to the transition zone between the central and peripheral myelin have suggested that the “transition zone” of the cranial nerves is susceptible to pressure from blood vessels [17, 18]. Therefore, the individual differences in the ‘transition zone’ of the cranial nerves may also be relevant to the HDS.
In the published literature, treatment of HDS in the pediatric and adolescent populations has been performed in the same manner as in elderly patients. Although medications are an effective first-line treatment option, when symptoms are refractory to them, surgical intervention is indicated. Many studies in the adult population reported the long-term efficacy of MVD. Pain relief was reported to be achieved in 73% of TN patients after 5 years, and in 76% of GPN patients after 2 years [4, 6]. Nevertheless, Bahgat et al. reported the characteristics, operative findings, and outcomes of TN patients aged ≤ 25 years. He identified that outcomes were not as good as those in the older population [19]. Several previous studies have reported that TN due to venous compression was recognized as a negative prognosis, which may be associated with MVD outcomes in such young patients [19, 20]. Also, fatal complications such as cranial nerve dysfunction (2%), stroke (0.3%), and death (0.2%) may occur. The second-choice neurosurgical treatment is gamma knife radiosurgery, which uses a focused radiation beam to sever the nerve root. However, recurrence rates were higher than in MVD [4,5,6]. Other surgical treatments include destruction in the ganglion or peripheral nerves, which can be performed chemically by glycerol blockade, mechanically by balloon compression, or thermically by RFT, with almost no major complications [4, 5]. RFT of the right mandibular nerve was performed for TN in our patient. This procedure, such as the approach to peripheral nerves or ganglion, can be used to achieve proper diagnosing of HDS. It is also an alternative therapy for MVD and easily performed at a low cost and can be repeated as necessary. However, the limitation is that it might be difficult for patients in younger age groups such as toddlers to cooperate during this procedure. Therefore, the utility and indications of these treatments for young patients require further investigations.
In conclusion, we report a very rare adolescent-onset combined HDS. GPN and TN were treated with MVD and RFT of the mandibular nerve, respectively, with no symptom recurrence for > 3 years to date. It is necessary to recognize that single and combined HDS may occur even in the pediatric or adolescent population. Symptom complaints might be atypical in pediatric–adolescent patients with HDS. Nevertheless, prompt diagnosis and management are crucial to improving patient outcomes.