Ultrasound-guided cervical selective nerve root block in the approach to cervical traumatic neuromas: a technical note

1. Instituto do Câncer do Estado de São Paulo (Icesp), São Paulo, SP, Brazil. 2. Instituto de Radiologia do Hospital das Clínicas da Universidade de São Paulo (InRad/HC-FMUSP), São Paulo, SP, Brazil. Correspondence: Dr. Vinícius Neves Marcos. Avenida Doutor Eneas Carvalho de Aguiar, 255, Cerqueira César. São Paulo, SP, Brazil, 05403-900. Email: viniciusnevesm@gmail.com. a. https://orcid.org/0000-0002-3921-0828; b. https://orcid.org/0000-0002-4751-0476; c. https://orcid.org/0000-0002-7058-6321; d. https://orcid.org/0000-0001-7041-3079; e. https://orcid.org/0000-0001-8836-1422. Received 9 December 2021. Accepted after revision 11 January 2022.


INTRODUCTION
A cervical traumatic neuroma (CTN), defined as nonneoplastic hyperplasia of a damaged peripheral nerve (1) , may be misinterpreted as a metastatic lymph node on postoperative ultrasound (2) . Fine needle aspiration biopsy (FNAB) of a CTN is quite painful (2) , so much so that acute exacerbation of pain during needle penetration into the nodule has been used as a diagnostic criterion for neuroma (3) .
The purpose of this case series was to describe a novel technique to reduce pain during FNAB of CTNs, by using an ultrasound-guided cervical selective nerve root block (SNRB).

PROCEDURE
Two patients with metastatic papillary thyroid carcinoma underwent total thyroidectomy and lateral neck dissection, after which they presented with cervical nodules on postoperative ultrasound. The nodules were not characteristic of lymph nodes and presented an intimate relationship with the C4 nerve root.
The examinations were performed with a versatile ultrasound system (LOGIQ E9; GE Healthcare, Waukesha, WI, USA) equipped with a high-frequency linear transducer (13-15 MHz). The cervical nodules were identified at cervical level III, and continuity with the C4 nerve root was detected in both patients. The nerve root, located between the scalenus medius and longus capitis muscles, was followed down to its emergence between the anterior and posterior tubercles of the transverse process ( Figure 1).
After the initial ultrasound analysis, the skin was appropriately prepared with antiseptic, and the transducer was draped with a sterile cover. A cutaneous nerve block was performed with a local anesthetic (lidocaine 1%). A 22-G needle was guided percutaneously with the in-plane  (Figure 2). After careful aspiration, 2 mL of lidocaine 1% were administered, under direct visualization by ultrasound, around the C4 root.
During the FNABs performed after the SNRB, there were no immediate complaints of pain. There were also no complications, and no additional therapy was immediately necessary. At one hour after the procedures, both patients reported mild pain (1/10 on a visual analogue scale) and were discharged with a prescription for oral analgesics. The cytological analysis revealed spindle cells, consistent with a diagnosis of neuroma, in both of the nodules biopsied.

DISCUSSION
This case series demonstrates a modified ultrasoundguided SNRB technique to use in the approach to CTNs, with efficient pain control during FNAB (summarized in Figure 3). To our knowledge, this technique has not previously been reported. It differs from conventional SNRB (4-7) in that it is first necessary to identify the neuroma and its root, then to follow it down to its emergence at the vertebral foramen, ensuring the correct location for the block.
A potential complication of C4 root block is phrenic nerve palsy (8) . However, that complication was not observed in either of the cases presented here or in any of the reports of SNRB in the literature (4-7) . One reason for this may be the selective nature of the block, in which a small dose of anesthetic is used and is injected into only one nerve root, without blocking the other phrenic nerve roots (4) .

CONCLUSION
In conclusion, the technique of using ultrasoundguided SNRB in the approach to CTNs, as described here,

Ultrasound-guided cervical SNRB for use in the approach to CTNs
Identify the cervical nodule* Check for continuity with the nerve root † Follow the nerve root down to its intervertebral foramen ‡ Inject the local anesthetic, under direct visualization, around the nerve root at its emergence § * In both cases, the nodule was located at cervical level III. † The nerve root was located in the cervical plexus, between the scalenus medius and longus capitis muscles. ‡ The nerve root should be followed by manipulating the transducer in an up-and-down motion until it reaches the neural foramen, which is located between the anterior and posterior tubercles of the transverse process, in a "U" shape. § The needle should be advanced caudally, at an angle of 45-60°, down to the region adjacent to the emergence of the nerve root, at the intervertebral foramen. The needle (arrows) is advanced caudally, at an angle of 45-60°, until its tip (asterisk) comes close to the C4 nerve root (yellow circle). The shape of the transverse process is delineated (blue line). The carotid artery (CA) and jugular vein (JV) are located medial to the needle track, whereas the sternocleidomastoid muscle (SCM) is located superficially.