The Investing Layer of the Deep Cervical Fascia: An Alternative Site for Ultrasound-guided Supraclavicular Nerve Block - A Cadaveric Anatomical Study

Abstract

Background: It is very well known that the supraclavicular nerve (SCN) which occupies the inferior part of the superficial cervical plexus basically originates from the ventral rami of C2-C4, then travels caudally into the investing layer of the deep cervical fascia (IL-DCF) alternatively termed the "prevertebral fascia."

Methods: This cadaveric study (a total of 6 soft-embalmed cadavers and bilateral dissections, i.e. 12 specimens) intended to ascertain the location of SCN within the layers of the IL-DCF. We hypothesized that ultrasonography identification of SCN within the IL-DCF and needle tip positioned between the layers of IL-DCF provide an alternative site for the blockade of the SCN.

Results: After dissection, we described a compact double-layered IL-DCF hosting the SCNs and a specific topographic arrangement at the C4 root with SCN lateral and C4 branches of the phrenic nerve medial to the C4.

Conclusion: We recommend another alternative site for the SCN block at a site in the compact double layer of IL-DCF. We conclude that a caudal site at the exit of SCN from the IL-DCF would be appropriate to perform the intervention.

Keywords: Cadaver; deep cervical fascia; dissection; supraclavicular nerve; ultrasonography.

Figure 1

(a) Bunch of hypoechoic structures arising from the C4 nerve root and coursing through the investing layer of the deep cervical fascia (IL-DCF]/prevertebral fascia, (b) Double layer of IL-DCF, (c) Needle tip in between the IL-DCF

Figure 2

(a) The prevertebral fascia (PVF)/(mild stain) encompassing the phrenic nerve (PN) (moderately stained). The lower deep middle scalene muscle (MSM) is stained (light stain) and not the upper superficial MSM (b) The supraclavicular nerve (SCN) (heavy stain) and the PN (heavy stain) emerging from the C4 nerve root (light stain) and engulfed by the PVF. The lower deep MSM is stained (light) (c) The PN its roots from C4 and C5 (heavy stain), the SCN (moderate stain), the C5 (heavy stain), and the C4 (light stain) are illustrated. The upper medial part of MSM is lightly stained. (d) The C4br (light stain) and SCN (moderate stain) originating from the C4 nerve root (light stained), C5br of PN (light stain), and the C5 nerve root (heavy stain) are depicted. The lower anterior scalenus muscle and the MSM are moderately stained. (e) The C4 nerve root is represented with a light stain, while the C3 nerve root is not stained. PVF: Prevertebral fascia (aka investing layer of the deep cervical fascia), MSM: Middle scalene muscle, ASM: Anterior scalene muscle, CCA: Common carotid artery, PN: Phrenic nerve, SCN: Supraclavicular nerve, AT-TP: Anterior tubercle of the transverse process, VrC5: Ventral root of C5

Figure 3

(a): The phrenic nerve (PN) and its roots from C4 and C5 are moderately stained, the supraclavicular nerve (SCN) is stained lightly, while the C4 and C5 are unstained (b) The distal SCN branches are moderately stained, the C4 is stained lightly, while the C4br of PN is moderately stained. The C3 is unstained. The unstained C2 with its dorsal and ventral root are envisaged. Muscular slips of anterior scalenus muscle are not stained. Origin of VA at the C2 FT is depicted. (c) The distal branches of SCN and PN are moderately stained. The main SCN, however, is lightly stained. The C4 is unstained. VA: Vertebral artery, FT: Foramen transversum, DR: Dorsal rami, VR: Ventral rami, AT: Anterior tubercle, Br of SCN: Branches of the supraclavicular nerve, C4rPN: Root from the 4^th cervical nerve