Classical trigeminal neuralgia is characterized by brief, recurrent, unilateral, electric shock-like pains limited to the distribution of one or more divisions of the trigeminal nerve. It is easily diagnosed and well-known to be induced by neurovascular compression of the trigeminal nerve. However, unilateral trigeminal neuralgia with concomitant continuous pain, formerly called atypical trigeminal neuralgia, is difficult to categorize and the cause of it is difficult to identify.
Here, the authors report a patient who presented with trigeminal neuralgia with concomitant continuous pain of unknown cause
A 45-year-old woman was on a flight and suffered from a sudden onset of right temporal pain for 30 min, followed by a tingling sensation on the right cheek. After she arrived at her destination, she experienced a throat blockage for approximately 20 min. Neurological examination only revealed a tingling sensation in the area of the second branch of the right trigeminal nerve (the maxillary nerve). Otolaryngological examinations were unremarkable, except for percussion pain from the upper right central incisor to the first molar and gingival sensory disturbance in those regions (Fig. 1). The patient was examined using head magnetic resonance imaging (MRI), which detected inflammatory findings in the right ethmoid sinus and slight fluid retention in the right sphenoid sinus (Fig. 2). No pathological findings in or around the brainstem and cisternal portion of the trigeminal nerve were noticed. Under a diagnosis of idiopathic trigeminal neuralgia, the woman received conservative treatment. Because her symptoms persisted, the patient revisited the neurologist 1 month after the onset, and an additional MRI scan revealed chronic sinusitis in the right sphenoid sinus (Fig. 3).
Timeline. This timeline shows the patient’s symptoms, imaging studies, and treatment.
Axial T2-weighted head MR image on the day following initial onset. This MR image reveals acute sphenoid sinusitis, including fluid (arrowheads).
Axial T2-weighted follow-up MR image 1 month after onset. This MR image reveals chronic sinusitis of the right greater wing, which is filled with mucosa and fluid (arrowheads), and the ethmoid sinus, which has thick mucosa (arrows).
Seven weeks after onset, the patient’s symptoms continued, such as a tingling sensation from the right side of her nose to around her upper lip, and, therefore, she visited our hospital for a further workup. During the entire period, she noticed no febrile episodes. Neurological examinations revealed only sensory disturbance on the second branch area of the right trigeminal nerve. Other cranial nerves were intact, and a blood examination revealed no abnormal findings. The CT examination indicated sphenoid sinusitis with a small amount of fluid retention. And the coronal thin-sliced bone CT revealed the absence of the bony boundary between the sizeable sphenoid sinus and maxillary nerve (Fig. 4).
Coronal cross-sectional CT images 7 weeks after onset. These coronal sinus CT images line the dorsal to the ventral side toward the bottom. They reveal a bone defect around the maxillary nerve facing the sphenoid sinus (arrowhead) as well as sphenoid sinusitis with fluid retention (asterisk).
According to these results, it was conceivable that her symptoms were caused by inflammation from sphenoid sinusitis that had spread to the maxillary nerve. The bone defects surrounding the maxillary nerve contributed to the spread of inflammation to the nerve. Because the symptoms were improving, the patient was conservatively followed up without any medication, and she was entirely symptom-free 5 months after onset.
In consideration of the pathophysiological mechanisms of the symptomatic progression of this patient, the following two mechanisms were postulated: barosinusitis and the anatomical variation of the sphenoid sinus.
Barosinusitis is an acute form of paranasal sinusitis. Changes in air pressure, such as during skydiving in a short period cause disturbances of the pressure balance in paranasal sinuses, resulting in sinus mucosal damage. Acute sinusitis, including barosinusitis, is usually limited to the sinus mucosa without bony destruction of the paranasal sinuses.
Anatomical Variation of the Sphenoid Sinus:
To clarify this mechanism, we examined her CT scans. In the coronal bone images from the thin-slice study, no bony boundary between the maxillary nerve and sphenoid sinus was observed. A precise examination of the CT images revealed no other chronic inflammatory changes. The symptoms of this patient had an acute onset, and no chronic changes were observed in the CT scans. According to this evidence, the pathological process of this patient was caused by acute sinusitis. The absence of bone between the maxillary nerve and sphenoid sinus was considered to be a long-lasting result, such as a congenital defect, but not to have been caused by bony destruction from a chronic inflammatory process.
Nerves without surrounding bone tissue are vulnerable to inflammation occurring in nearby tissues. In these situations, congenital bone defects surrounding the maxillary nerve can cause neurological symptoms immediately after sphenoid sinusitis.
In conclusion, the pathophysiological mechanisms of trigeminal neuralgia without neurovascular compression findings in the trigeminal nerve have been overlooked and treated as idiopathic trigeminal neuralgia.