Changes of sonographic, magnetic resonance tomographic, electromyographic, and histopathologic findings within a 2-month period of examinations after experimental muscle denervation

Abstract

This study compares sonographical, histopathological, magnetic resonance imaging (MRI), and electromyographical (EMG) findings following acute muscle denervation. We performed an experimental denervation of the supraspinatus and infraspinatus muscles on 35 New Zealand white rabbits by segment resection of the suprascapular nerve. The sonographical appearance of the supraspinatus muscle was followed and documented at short time intervals within a 2-month follow-up period. The sonographical, histopathological, and MRI changes due to denervation suggest a regular pattern. Apart from the reduction of the muscle diameter, there were considerable sonographical signs of denervation with an increase of echointensity and inhomogenicity of echotexture that appeared on day 14 after injury, and progressed continuously with time. MRI revealed a remarkable increase in signal intensity 3 weeks after denervation and reproducible T2 times. Pathological spontaneous activity on EMG could also be detected from day 14 after injury. Conventional histopathological staining methods (H&E, NADH, ATPase, basic and acid phosphatase) confirmed denervation and absence of reinnervation. The first nonspecific histopathological changes were seen 11 days after denervation in the form of moderately atrophic fibers. Typical histopathological signs of denervation appeared 3 weeks after nerve dissection. In summary, EMG, ultrasound, MRI, and histopathology each showed first abnormalities after about 2 weeks. In addition to EMG, sonography and MRI can document the course of muscle atrophy and mesenchymal abnormalities in neurogenic muscle lesions.

MR imaging evaluation of suprascapular nerve entrapment

“…A high T2 signal intensity was diagnosed in the supra-and infraspinatus muscles. This finding was corroborated by Küllmer et al's experimental study pertaining to complete suprascapular nerve section in the rabbit [35]. Küllmer et al identified an increasingly high-intensity T2-weighted signal with a peak between days 21 and 35 after nerve section.…”

“…Muscular edema may be explained by hydration modifications of the muscular mass, in the case of denervated muscles [27,33,34,35]. Signal modifications of muscles on T2-weighted images appear as early as the fifteenth day of the onset of neuropathy [34].…”

2D SPLASH: a new method to determine the fatty infiltration of the rotator cuff muscles

“…One may assume that in terms of long-standing rotator cuff tears, two aspects, the neurogenic and the inactivity-related one, play a role in atrophy and fatty infiltration of the rotator cuff muscles. From experimental data, both phenomena are known to end in both atrophy and fatty infiltration [6,7]. The influence of both factors may possibly be individually different, leading to a more atrophic or more fatty degeneration.…”

“…In an experimental study with rabbits [6], fatty infiltration and atrophy of the supraspinatus muscle have been shown as early as 4 weeks, with a maximum at 6 weeks, after detachment of the tendon from the osseous insertion. Kullmer and colleagues [7] compared sonographical, histopathological, MRI and electromyographical findings following experimental denervation of the suprascapular nerve in a rabbit study. MRI has shown a decrease of the muscle diameter and an increased signal intensity of the muscle assessed visually after 21 days with its maximum after 2 months.…”

Suprascapular neuropathy related to rotator cuff tears: A short review

“…Furthermore, because SSN entrapment related to rotator cuff tears is thought to be a dynamic phenomenon, the co-existence of SSN neuropathy and rotator cuff tears may not always be demonstrable on EMG 11 . Magnetic resonance imaging is also helpful in identifying changes in the supraspinatus and infraspinatus muscles secondary to denervation, such as decreased muscle bulk, fatty infiltration and homogeneous high-signal intensity on T2-weighted images [37][38][39][40] . Beeler et al 37 observed the appearance of fatty infiltration and muscle atrophy on magnetic resonance imaging when comparing cases of rotator cuff tears and suprascapular neuropathy.…”