A Case of the Scalenus Anterior Muscle Passing Behind the Left Subclavian Artery

Abstract

The scalenus anterior muscle was found to pass behind the left subclavian artery and the first thoracic nerve in a 95-year-old Japanese woman. The scalenus anterior muscle originates from the fifth and sixth cervical vertebrae and inserts on the first rib more dorsal than typical. It is innervated by the fifth and seventh cervical nerves. The muscle belly is thin. The scalenus minimus was not found. The left vertebral artery originates from the aortic arch and enters the transverse foramen of the fifth cervical vertebra. The primary vertebral artery arises from the costocervical artery. The internal thoracic artery originates from the subclavian artery more distally than typical. The axillary artery crosses the brachial plexus between the eighth cervical and first thoracic nerves. Because the first thoracic nerve joins the brachial plexus more distally than usual, the plexus has no typical inferior trunk. Comparative anatomy shows that the muscles, nerves and arteries of the lateral cervical region of the present case maintains primitive characteristics. From the functional viewpoint, the mechanical efficiency of the scalenus anterior muscle is probably lower than usual due to the lower point of origin and the dorsal shift of the insertion.

Bilateral subclavian arteries passing in front of the scalenus anterior muscles

“…To our knowledge, no case of bilateral subclavian arteries passing in front of the scalenus anterior muscles has been reported. Adachi (1928) and seven others (Mori, 1941; Komatsu et al ., 1984; Inuzuka, 1989; Takafuji & Sato, 1991; Okamoto et al ., 1997; Kodama, 2000; Yuda et al ., 2000) have reported 14 cases of a unilateral subclavian artery passing in front of the scalenus anterior muscle.…”

A Case of the Scalenus Anterior Muscle Lying Behind the Fifth Cervical Nerve Root

“…Previously, a "major" variation relating to the scalenus anterior muscle such as the subclavian artery passing before the muscle (Dolgo-Saburoff, 1933;Inuzuka, 1989;Harry et al , 1997) has been discussed in the context of vascular embryology. However, we thought that minute muscle dissection and nerve fiber analysis might reveal both hidden and conspicuous changes concerning the innervation, since such a "minor" change of the topography as seen in the present variant (Fig.…”

Methods to Ease Placement of Stimulating Catheters During In-Plane Ultrasound-Guided Femoral Nerve Block

“…The likely reason for the described separation in our case may be due to the insertion of the anterior scalene muscle between the subclavian artery and the brachial plexus. 8 The anatomy of supraclavicular fossa may be prone for a wide range of variations including aberrant course of nerves, blood vessels, muscles, and bone (eg, cervical rib). Further studies are needed to confirm the true incidence of such variations and its significance to regional anesthesia practice.…”