Identification of Continuity of Transected Nerve on Sonography After Neck Dissection: Direct Sign of Traumatic Neuroma

Introduction

T raumatic or amputation neuroma is a non-neoplastic proliferation of nerve tissue that occurs at the end of an injured nerve after trauma or surgery. In the head and neck regions, especially after neck dissection for malignancy, traumatic neuroma may be easily confused with a metastatic lymph node, thereby increasing patient anxiety and necessitating fine needle aspiration (FNA) (1 –3). To date, several reports have documented the indirect ultrasonographic (US) features of traumatic neuroma after neck dissection; among the characteristics distinguishing traumatic neuroma from metastatic lymph node are the frequent occurrence of a central hyperechoic area, a smaller short axis diameter, and a smaller short-to-long axis ratio (1,2). However, there have been no reports showing the direct continuity of a transected nerve after neck dissection in patients with traumatic neuroma. We describe here a patient with traumatic neuroma who showed a direct US sign after total thyroidectomy with modified radical neck dissection (MRND).

Patient

A 61-year-old man was referred to the radiology department for postoperative surveillance of tumor recurrence. He had undergone a total thyroidectomy with right MRND for papillary thyroid carcinoma (PTC) 7.5 years earlier and a left MRND for lymph node metastasis 1 year earlier. At the time of US examination, the patient was taking levothyroxine and had a thyroid-stimulating hormone (TSH) concentration of 0.08 mIU/L and a serum thyroglobulin (Tg) concentration of 0.36 ng/mL.

The US examination showed a 1.0 cm-sized nodule in his right lateral neck, located in the posterolateral aspect of the common carotid artery at level III according to imaging-based nodal classification (4). The nodule had an oval shape, ill-defined margin, and heterogeneous hypoechogenicity, and was first suspected of being a metastatic lymph node (Fig. 1A, B). However, when the position of the US transducer was changed to the oblique plane, then a thin, cord-like, hypoechoic structure was found to be connected to the nodule (Fig. 1C). This structure passed between the longus capitis and scalenus medius muscles in an upward direction, and was ultimately located in the groove of the right transverse process of the C4 vertebra (Fig. 1D; Supplementary Video available online at www.liebertonline.com/thy). Although the patient did not complain of painful hyperesthesia or paresthesia in his neck during the entire US examination, we concluded that the nodule was a traumatic neuroma and did not perform an unnecessary FNA based on this anatomic relation.

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FIG. 1.

Transverse (A) and longitudinal (B) US images of the right side of the neck, showing an ill-defined, oval heterogeneously echoic solid nodule in the right level III. (C) Tracing of the nodule in the superior and medial directions, showing its connection to a thin, cord-like, hypoechoic structure (arrow) passing between the longus capitis and scalenus medius muscles in an upward direction. (D) Transverse US image slightly upward to A, showing that the hypoechoic cord-like structure is located in the groove of the right transverse process of the C4 vertebra, suggesting the C4 spinal nerve. IJV, internal jugular vein; CA, carotid artery; LCo, longus colli muscle; LC, longus capitis muscle; TP, transverse process; US, ultrasonographic.

The patient was followed up for 1.5 years after the US examination and has shown no clinical or serologic evidence of tumor recurrence. A final serologic test showed that his TSH level was 0.04 mIU/L, and his serum Tg level was 0.028 ng/mL.

Discussion

Traumatic neuroma develops at the proximal end of the transected nerve as a reparative process of the injured nerve. Therefore, identification of a transected nerve continuous with a heterogeneous solid nodule at the expected position may be diagnostic of a traumatic neuroma (5,6). Magnetic resonance imaging has shown traumatic neuromas in continuity with injured or transected nerves in the lower extremities after amputation (7). To date, however, no US studies have shown the continuity of transected nerves after neck dissection in the head and neck region.

The US in our patient showed a transected nerve with direct continuity to a traumatic neuroma after neck dissection for PTC. The transected nerve was identified as a thin cord-like hypoechoic structure between the longus capitis and scalene medius muscles, passing over the transverse process of the C4 vertebra, between the anterior and the posterior tubercles. These US findings resulted in a confident diagnosis of the hypoechoic nodule in the right lateral neck as a traumatic neuroma originating from the branch of the ventral rami of the cervical spinal nerve.

After neck dissection, traumatic neuroma usually arises from injury to the peripheral sensory nerves of the cervical plexus, such as the great auricular, cutaneous cervical, and supraclavicular nerves (8 –11). Using a high-resolution transducer, US detection and tracing of the main branches of the lower cervical plexus from the C3 and C4 spinal nerves in the neck are technically feasible from the transverse process passing between the longus capitis and scalene medius muscles (Fig. 2A, B).

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FIG. 2.

(A) Schematic drawing of a transverse section of the neck at the C4 level. The fourth cervical nerve root (dotted line) exits from the spinal canal and passes through the corresponding neural foramen (arrow). The nerve (continuous line) courses inferolaterally between the longus capitis and scalenus medius muscles, and is then located in the posterior cervical triangle. (B) Contrast-enhanced axial computed tomography scan of the neck at the C4 level. The fourth cervical nerve is visible in the expected course of the neck (arrow). a, sternocleidomastoid muscle; b, longus colli muscle; c, longus capitis muscle; d, scalenus medius muscle.

Previous studies have reported several indirect US features of traumatic neuroma in the head and neck regions; these studies have focused on distinguishing between traumatic neuroma and metastatic lymph node by using characteristics such as echogenicity, size, and location. Although US can help diagnose traumatic neuroma, there are overlaps between traumatic neuroma and metastatic lymph node, thus making these findings suggestive rather than diagnostic. In addition, none of these reports showed direct continuity of the transected nerve, perhaps due to the size discrepancy of the transected nerves between the knee and head and neck region (1,2). Nevertheless, understanding of related anatomy may be crucial in detecting continuity of the transected nerve.

Conclusion

We describe here a patient with a traumatic neuroma arising from the branches of the cervical plexus after neck dissection. The US may be used to directly visualize the continuity of the transected nerve with the traumatic neuroma after neck dissection in the head and neck regions.