Introduction
Perineural cysts are most commonly identified in the sacral region and are rarely reported in the cervical spine [1,2]. Although they are typically asymptomatic, cervical perineural cysts can occasionally present with radicular symptoms, even in the absence of significant disc pathology [2,3]. When present in the cervical region, these cysts are usually solitary and arise at the dorsal root ganglion (DRG), where the dural sleeve transitions into the nerve sheath [3].
However, perineural cysts are not confined to the DRG, and those arising proximal to the DRG have not been well characterized. These proximal lesions may also produce cervical radicular pain, regardless of the presence of concomitant cervical disc herniation, similar to cysts located at the DRG.
Here, we report a case of cervical perineural cysts occurring both at and, more importantly, proximal to the DRG within the C6 nerve root sleeve. The proximal cyst directly compressed the C6 dorsal nerve root, whereas the coexisting C5–C6 disc herniation did not result in significant nerve root compression. This case highlights the importance of recognizing cysts arising proximal to the DRG when evaluating patients with symptoms of cervical radiculopathy.
Case Report
A 53-year-old woman presented to the Department of Physical Medicine and Rehabilitation outpatient clinic with a 1-year history of intermittent left arm pain and persistent numbness involving the left thumb, index finger, and thenar region.
She had previously been evaluated at another hospital, where carpal tunnel syndrome was suspected based on her hand paresthesia. She underwent two steroid injections into the carpal tunnel; however, her symptoms did not improve. Given the poor response to peripheral treatment and the presence of neck pain, a cervical etiology was considered. Cervical radiographs and magnetic resonance imaging (MRI) reportedly demonstrated disc space narrowing at C5–C6 and C6–C7, with herniated intervertebral discs at the corresponding levels. Two interlaminar cervical epidural steroid injections partially improved her neck pain; however, numbness in the left upper limb persisted.
At presentation to our clinic, neurological examination revealed decreased light-touch and pinprick sensation in the left C6 dermatome. Muscle strength was normal in all upper extremity muscle groups, and deep tendon reflexes were symmetric.
Review of prior cervical MRI demonstrated a central-to-left C5–C6 disc herniation that mildly effaced the ventral epidural space without significant compression or displacement of the left C6 nerve root (Fig. 1A). A central C6–C7 disc herniation was also present, without foraminal narrowing or contact with the C7 nerve root (Fig. 1B).
Notably, at the level of the left C6 nerve root, two distinct cystic lesions were identified (Fig. 1C, D). One was a perineural cyst located at the DRG within the nerve root sleeve, consistent with the typical anatomical location. The second cyst was located proximal to the DRG, more medially within the neural foramen and closer to the dural sac—an atypical location. The proximal cyst, involving the ventral nerve root, directly compressed the left C6 dorsal nerve root.
Nerve conduction studies (NCSs) demonstrated normal sensory nerve action potentials (SNAPs) in the left median, ulnar, and superficial radial nerves, as well as normal compound motor action potentials in the median and ulnar nerves (Table 1). Needle electromyography (EMG) of the left cervical paraspinal and upper extremity muscles showed no abnormal spontaneous activity or motor unit changes (Table 2). Bilateral median somatosensory evoked potentials (SEPs) were within normal limits (Table 3).
The patient was advised to avoid excessive cervical flexion and extension and was prescribed pregabalin 75 mg and pelubiprofen 45 mg twice daily for 1 month. She did not attend the scheduled follow-up visit at 1 month due to substantial symptom improvement, with only intermittent recurrence of pain.
Discussion
Extradural meningeal cysts were classified by Nabors et al. [1] into type I and type II lesions according to the presence of spinal nerve root tissue within the cyst wall or lumen. Perineural cysts (Nabors type II) are cerebrospinal fluid-filled dilatations that contain spinal nerve root fibers within the cyst wall or lumen. They most commonly occur in the sacral region at the DRG, where the dural sleeve transitions into the nerve sheath [1,4]. Cervical perineural cysts are rare and, when present, are typically solitary and confined to the DRG level [2,3].
The present case is notable for the presence of a perineural cyst located proximal to the DRG within the cervical nerve root sleeve. To our knowledge, perineural cysts occurring proximal to the DRG have been described only rarely. This finding challenges the traditional view that perineural cysts arise exclusively at the DRG and broadens the recognized anatomical spectrum of Nabors type II cysts.
Several mechanisms have been proposed for cyst formation, including congenital dural weakness, repetitive microtrauma, inflammation, hemorrhage, and altered cerebrospinal fluid dynamics involving a ‘ball-valve’ effect [4-7]. Although the DRG is considered the most vulnerable site because of the dural-perineurial transition, similar structural weaknesses may also exist proximally within the dural sleeve, particularly in the presence of adjacent disc herniation. In this case, the C5–C6 disc herniation may have contributed to localized dural stress or impaired cerebrospinal fluid flow, thereby promoting cyst formation both at and proximal to the DRG.
The patient's symptoms were suggestive of C6 radiculopathy. Although MRI revealed a central-to-left C5–C6 disc herniation, it caused only mild indentation of the ventral epidural space without significant nerve root compression and therefore could not fully account for the patient's persistent symptoms. In contrast, the proximal perineural cyst directly compressed the C6 dorsal nerve root. Previous studies have reported that cervical perineural cysts confined to the DRG can produce radicular pain; however, these cysts are more commonly incidental and asymptomatic [2,5]. Given these considerations, the patient's symptoms were unlikely to have been explained by the DRG-level cyst alone. Instead, it is more plausible that the proximal perineural cyst mechanically compressed the sensory root, thereby contributing to the patient's radicular symptoms.
Electrodiagnostic studies were normal. This finding may be explained by the fact that the perineural cyst mechanically compressed the sensory nerve root. A perineural cyst involving the ventral nerve root would be expected to exert minimal influence on motor axons, which may explain the absence of denervation potentials on EMG and the lack of motor weakness in this patient. In addition, compression of the preganglionic sensory nerve root would preserve the DRG, resulting in intact SNAPs on sensory NCS. Median SEPs were also normal; however, because they reflect summated conduction across multiple segments, a focal root lesion may not be detected. Dermatomal SEPs, which assess conduction from a single dermatome, have been reported to be more sensitive for detecting segmental radiculopathy and might have provided greater diagnostic yield in this case.
As demonstrated in this case, perineural cysts may occur not only at the DRG but also proximally within the cervical nerve root sleeve, and such atypical locations may produce clinically significant radicular symptoms. Clinicians should consider proximal perineural cysts in the differential diagnosis of cervical radiculopathy, particularly when imaging findings are discordant with the neurological presentation. Careful correlation of perineural cysts proximal to the DRG identified on MRI with detailed sensory examination and electrodiagnostic assessment may enhance diagnostic accuracy and help prevent misattribution of symptoms to incidental disc pathology.
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