Pictorial reviewMRI of brachial plexopathies
Introduction
Magnetic resonance imaging (MRI) is the primary imaging technique in the evaluation of brachial plexus pathology.1, 2 Imaging has an important role in the identification, localization, and characterization of the cause, which may be inadequately evaluated by clinical examination or electrophysiological studies. MRI enables the differentiation of preganglionic from postganglionic injuries, a distinction that is critical in management decisions.3 Improvements in MRI technique have helped in detecting changes in signal intensity of nerves, subtle enhancement, and in detecting perineural pathology, thereby refining the differential diagnosis.1
Section snippets
Normal plexus anatomy
The brachial plexus is formed by the ventral rami of C5–T1, with or without minor branches from C4 and T2.4, 5 Anatomically it is divided into five segments: roots, trunks, divisions, cords, and terminal branches.4, 5 The supraclavicular plexus includes the roots in the interscalene triangle and three trunks (upper, middle and lower) at the lateral border of middle scalene muscle.6 The retroclavicular plexus contains the divisions (anterior and posterior divisions of the trunks) in the
MRI technique
Most patients were examined using a 1.5 T MRI system (Magnetom Avanto, Siemens, Erlangen, Germany) using both cervical and body coils; the remaining patients were examined using a 3 T MRI system (Intera Achieva, Philips, Best, Netherland) using a neurovascular coil. The 1.5 T system is now used for these studies, with the patient in the supine position and arms at their sides. The surface coil is used for the spinal cord and exiting nerve roots, while the body coil is useful to image the plexus
Normal MRI appearances
High field strength MRI, with its excellent soft-tissue contrast and multiplanar capabilities, allows good delineation of the brachial plexus. Normal anatomy of the brachial plexus is well demonstrated on coronal and sagittal images, and is best displayed on T1-weighted images. The sagittal oblique plane (Fig. 3) has the advantage of depicting the course of the brachial plexus in cross-section, the most reliable imaging plane for the visualization of the trunks, divisions, cords, and branches
Brachial plexopathies
Causes of brachial plexopathy can broadly be classified into two categories: non-traumatic and traumatic causes.
Hereditary motor–sensory neuropathy
Hereditary motor–sensory neuropathy (HSMN), also known as hypertrophic neuropathy or Charcot–Marie–Tooth (CMT) syndrome, is characterized by focal or diffuse peripheral nerve enlargement with limb atrophy.8 Most patients present in the first or second decade; others in young or mid-adulthood. This condition can mimic plexiform neurofibroma and chronic inflammatory demyelinating polyneuropathy (CIDP) on MRI. HSMN and CIDP show myelin and axonal loss. Absence of inflammatory infiltrates, presence
Infective or inflammatory
Brachial plexus neuritis may be of unknown cause, but may also be associated with conditions such as viral or bacterial infection and vaccination. Neuritis is preceded by infection in about 25% of cases, follows vaccinations in 15% of cases,10 and can also be post-traumatic or post-surgical. Patients may present with sudden onset of pain, followed by weakness and paraesthesia, or may have only sensory abnormalities. Differentiation of this entity from cervical radiculopathy, a common mimic of
Primary neurogenic tumours
Primary neoplasms of the brachial plexus are uncommon, but include both benign and malignant neurogenic tumours.13, 14 The four primary tumours are neuroma, schwannoma, neurofibroma (Fig. 9) and neurofibrosarcoma. MRI may be use to differentiate between neurofibroma and schwannoma, a distinction crucial for surgical planning. The “target sign” with peripheral high signal and central low intensity on T2-weighted images favours a neurofibroma (58% neurofibromas, compared with 15% in schwannoma),
Metastasis and tumours in the vicinity of the brachial plexus
Secondary tumours involving the brachial plexus and lesions in the neck and axilla are more common than primary tumours.7 Breast and lung cancers are the most common malignancies that metastasize to the brachial plexus by contiguous spread (Fig. 10). Brachial plexopathy due to metastasis is usually unilateral and more focal. Signal intensity mimics the primary tumour; history of known malignancy aids the diagnosis. Fig. 11 is a case of peripheral neurolymphomatosis, also called perineural
Radiation plexopathy
This is a subacute to chronic plexopathy with an incidence of less than 1%. It has a delayed onset, 6 month to over 20 years post-radiation, with a peak onset at 10–20 months.7 Imaging findings include mild, smooth, diffuse T2 hyperintensity without focal nodular involvement, with or without enhancement of multiple plexus elements. The upper brachial plexus (C5–7) is more commonly involved than the lower brachial plexus (C-8,T1).20 In chronic cases, along with architectural distortion of
Entrapment syndrome
Entrapment syndrome is also called thoracic outlet (TOS) syndrome.21 Commonly, cervical rib, elongated C7 transverse process, other congenital fibromuscular anomalies, muscle hypertrophy (scalenus, subclavius or pectoralis minor muscles), and posture cause neuropathic TOS. This may be due to compression or elongation of neurovascular bundles as they pass through the compartments (interscalene triangle, costoclavicular space, and retropectoralis minor space) of the thoracic outlet.6, 21 Raising
Traumatic brachial plexopathies
Most of the adult brachial plexus palsies are post-traumatic injuries, secondary to high-energy forces, such as motorcycle accidents. In infants, brachial plexus palsy can be secondary to excessive traction on the plexus during difficult (often breech or forceps) deliveries. The patient may present with pain and paralysis of involved limb. Clinical examination cannot reliably distinguish between the pre- and postganglionic injuries. This information is critical for surgical management options
Conclusion
MRI is an excellent tool in the evaluation of brachial plexus pathology. Imaging helps in the identification and accurate localization of an abnormality, and often enables specific characterization or narrowing of the differential diagnoses. Conditions that may mimic brachial plexus pathology (such as cervical spondylosis) can be ruled out. The ability to localize and assess neural and perineural changes allows the differentiation of the wide spectrum of pathology in this region, and aids in
Acknowledgement
The authors thank Mr Niyas Ahamed, Engineer, Dept. of Radiology, Christian Medical College, Vellore, India.
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