Visualization of the Long Thoracic Nerve using High-Resolution Sonography

Abstract

Purpose: The long thoracic nerve (LTN) innervates the serratus anterior muscle (SA) which plays an important role in shoulder function. Evaluation of the LTN has so far been restricted to clinical assessment and partly electromyography and neurography. Progress of high-resolution ultrasound (HRUS) increasingly enables visualization of small peripheral nerves and their pathologies. We therefore aimed at (a) clarifying the possibility of visualization of the LTN from its origin to the most distal point in the supraclavicular region visible and (b) developing an ultrasound protocol for routine use. We further present two cases of patients with LTN pathology.

Methods: The study consisted of two parts: Part 1 included 4 non-enbalmed human bodies in whom the LTN (n = 8) was located and then marked by ink injection. Correct identification was confirmed by anatomical dissection. Part 2 included 20 healthy volunteers whose LTN (n = 40) was assessed independently by two radiologists. Identification of the LTN was defined as consensus in recorded images.

Results: LTN was clearly visible in all anatomical specimens and volunteers using HRUS and could be followed until the second slip of the serratus anterior muscle from the supraclavicular region. In anatomical specimens, dissection confirmed HRUS findings. For all volunteers, consensus was obtained. The mean nerve diameter was 1.6 mm ± 0.3 (range 1.1 – 2.1 mm) after the formation of the main trunk.

Discussion: We hereby confirm a reliable possibility of visualization of the LTN in anatomical specimens as well as in volunteers. We encourage HRUS of the LTN to be part of the diagnostic work-up in patients presenting with scapular winging, shoulder weakness or pain of unknown origin.

Zusammenfassung

Ziel: Der Nervus thoracicus longus (LTN) innerviert den Musculus serratus anterior (SA), der eine wichtige Rolle für die Funktion des Schultergelenks spielt. Seine Evaluierung war bisher auf klinische Untersuchung und teilweise Elektroneurografie und Elektromyografie beschränkt. Der Fortschritt des hochauflösenden Ultraschalls (HRUS) ermöglicht zunehmend die Darstellung kleiner peripherer Nerven und deren Pathologien. Ziel der vorliegenden Arbeit war es (a) die Visualisierbarkeit des LTN vom Ursprung bis zum distalsten einsehbaren Punkt supraklavikulär zu dokumentieren und (b) ein Ultraschallprotokoll für den Routineeinsatz zu erstellen. Darüber hinaus präsentieren wir zwei Fälle mit LTN-Pathologien.

Material und Methoden: Die Studie bestand aus zwei Teilen: Teil 1 umfasste die Ultraschalldarstellung des LTN, seine Markierung mittels Tinte und anschließende Sektion in 4 frischen anatomischen Präparaten (n = 8). Teil 2 umfasste die Darstellung des LTN in 20 gesunden Freiwilligen (n = 40). Die Identifikation erfolgte im Konsens durch zwei Untersucher.

Ergebnisse: Der LTN konnte in allen anatomischen Präparaten und Probanden identifiziert werden. Die Darstellung von supraklavikulär aus gelang bis zur zweiten Zacke des SA. Die korrekte Identifikation wurde in den Präparaten durch Dissektion bestätigt. Für alle Probanden wurde Konsens erzielt. Der durchschnittliche Durchmesser des LTN lag bei 1,6 mm ± 0,3 (Range 1,1 – 2,1 mm) nach der Formierung des Hauptstammes.

Schlussfolgerung: Die Ergebnisse dieser Studie bestätigen die zuverlässige Visualisierbarkeit des LTN mittels HRUS und legen den zukünftigen routinemäßigen Einsatz in der Diagnostik bei PatientInnen mit Scapula alata, Schwäche oder Schmerzen unklarer Genese im Schultergelenk nahe.

Key words

normal variants - long thoracic nerve - scapula alata - shoulder pain

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