Intractable Occipital Neuralgia Caused by an Entrapment in the Semispinalis Capitis
A 66-year-old, female developed episode of paroxysmal, severe lancinating pain in her left occipital region, correlating to the area of the GON. Mild pain had started 6 months before and had increased progressively in severity and frequency. The pain originated at the occipitocervical junction and radiated to the vertex. It was sharp, lancinating in nature and exacerbating factors such as neck flexion were not found. At times, it was associated with nausea and photosensitivity. Attacks of lancinating pain with a severity score of 9/10 on a visual analog scale (VAS) lasted for a few seconds. A residual dull aching pain remained between the attacks (score 5/10 on a VAS). The frequency of paroxysmal pain progressively increased and eventually became almost constant for 1 month until, she became bed-ridden without being able to do her daily activities. On examination, a painful, dysesthetic allodynia was present over the left GON distribution. During evaluation, she was placed on more than 7 medications that included non-steroidal anti-inflammatory drugs (NSAIDs), antiemetics, anticonvulsants including carbamazepine, lamotrigine, and gabapentin, β-blockers, anticholinergics, steroids, and triptans. Opioids including 40 mg of IRcodon and transdermal fentanyl patch were tried in vain. A block of the GON could provide transient relief of neuralgic pain for only about 1 hour. Radiofrequency ablation of the GON was tried with minimal effect. Intramuscular injection of diclofenac sodium could provide only 2-3 hours of partial relief. The flexion and extension views of the cervical spine showed no evidence of subluxation or arthritic change. The magnetic resonance imaging (MRI) of the brain and cervical spine was obtained and was negative for any mass lesion and upper cervical degenerative change. On the T2-weighted sequence, an anomalously low PICA loop was observed on the left. The distal loop extended to the level of the C1 lamina (). To evaluate the possibility of the low-lying PICA loop compressing the upper cervical roots, a computed tomographic myelography was performed and showed the same finding of the MRI () : the left PICA was low so that it extended to the level of C1. A superficial vascular ultrasound with a 17 MHz linear transducer showed no abnormal vascular contact along the course of the GON.\nConsidering the intractability of the occipital neuralgia and the possible vascular compression of the upper cervical root, the explorations of the GON, the dorsal rami of the C2 root, and intradural C2 root were planned. A linear midline incision was made and the dissection was carried down along the course of the GON. Upon entering the semispinalis perforation of the semispinalis caipits, tight constriction and entrapment of the GON was noted (). Careful dissection was performed to leave a generous amount of space surrounding the entrapment site to prevent postoperative constriction. There was no compression upon dissection of the proximal course of the GON around the inferior oblique muscle and the proximal dorsal rami of the C2 lateral to the foramen (). After left-sided hemilaminotomy of C1 and dural opening, the low-lying PICA loop was not found to be in contact with the left side of the C2 posterior root (). At the conclusion of the operation, the overlying wounds were closed avoiding any remnant constriction or compression along the course of the GON. Immediately upon awakening from the anesthesia, the patient was free of severe lancinating, neuralgic pain and experienced only the typical incisional pain of a surgical procedure. All medications including gabapentin, NSAIDs, and opioids were discontinued until postoperative three months. During 12 months' follow-up, she had no attack of lancinating pain of occipital neuralgia, although she experienced some paresthesia in her left occipital region. No hypesthesia and no allodynia were found at the follow-up.