The MRI imaging findings of patients presented to department of Neuroimaging and Intervention in our institute with Brachial plexopathies were documented ,analyzed in conjunction with normal anatomy

ANATOMY OF BRACHIAL PLEXUS:

The brachial plexus is complex neural network that provides sensory and motor innervation to the chest, shoulder, arm, and hand. It arises from the C5 to T1 spinal nerves shown in Fig1, but anatomical variations can occur. The prefixed brachial plexus involves contributions from C4 to C7, while postfixed plexus incorporates fibers from C6 to T2. Rarely, combination of both variants can be present, with contributions spanning C4 to T2.

Fig 1: Roots and trunks of brachial plexus

BONY LANDMARKS:

The brachial plexus is network of nerves that innervates the upper limb and several key anatomical landmarks are crucial for its identification.

The first landmark is the neural foramen, where brachial plexus originates. On axial and sagittal images, the ventral and dorsal roots merge to form spinal nerve.Dorsal root ganglion (DRG), located just proximal to union of the roots, contains first-order sensory nerve cell bodies and helps differentiate preganglionic from postganglionic injuries.

Dorsal nerve root ganglia is the landmark of preganglionic and postganglionic nerves shown in Fig2.

Fig 2: Preganglionic and postganglionic nerves

The roots of brachial plexus are positioned anteriorly toward the interscalene triangle. In sagittal imaging, these roots appear as five stacked points shown in Fig3. T1 root is below the first rib, while the C8 root is above it, providing  helpful reference for locating the roots on imaging.The second key landmark is interscalene triangle shown in Fig3,formed by anterior and middle scalene muscles. These muscles originate from cervical spine and are inserted into first rib. The trunks of  brachial plexus appear here as three stacked points on sagittal images.

Fig 3: Roots appears as five stack points on sagittal view and trunks as three stack points in the interscalene triangle

The upper trunk is formed by C5 and C6 roots, the middle trunk continues from C7 root, and the lower trunk results from C8 and T1 roots. The upper and middle trunks are superior to the subclavian artery, while the lower trunk is posterior.As the trunks continue inferolaterally, they reach the lateral border of first rib, marking the third landmark. Here, each trunk divides into anterior and posterior divisions, forming triangular cluster of six points, shown in Fig4 located just above subclavian artery.The fourth landmark is medial border of coracoid process, where the divisions form lateral, posterior, and medial cords, arranged relative to the axillary artery. On sagittal images,the cords form distinctive "paw-print" shape shown in Fig4.

Fig 4: Divisions as triangular cluster of six points on sagittal view and cords form a paw print appearance above the axillary artery

Finally, at the lateral border of pectoralis minor muscle, the cords separate into four terminal branches. These include the median,musculocutaneous,radial,ulnar and axillary nerves, which are arranged in quadrants around the axillary artery in Fig5.

Fig 5: Branches arranged as quadrants about the axillary artery

Coronal views of brachial plexus shows the course of brachial plexus from roots to branches with key landmarks in Fig6,Fig7

Fig 6: Roots and trunks with first rib as landmark

Fig 7: Cords and branches on coronal view

Coronal 3D Nerve view shows the course of brachial plexus from roots to branches shown in Fig8, and pictorial representation with all the branches in Fig9 and their root values are shown in Fig10.

Fig 8: 3D nerve view shows the course of brachial plexus

Fig 9: Pictorial representation of brachial plexus from roots to branches

Fig 10: Branches of brachial plexus with its nerve roots

Course of Brachial plexus with subclavian and axillary artery shown in Fig 11.The upper trunk lies anterior to subclavian artery.Cords lie about the axillary artery.At the outer border of the first rib, subclavian artery becomes the axillary artery.

Fig 11: Course of brachial plexus in relation to the arteries

MUSCLES INNERVATION :

Shoulder,chest wall and rotator cuff muscles innervation by the brachial plexus shown in fig12,fig13 along with its action helps to localize lesions based on the symptoms caused by the affected branches,shown in fig14

Fig 12: Pictorial representation of Shoulder muscles innervation with root values

Fig 13: Rotator cuff muscles innervation by brachial plexus

Fig 14: Muscles innervation by brachial plexus with their actions

BRACHIAL PLEXOPATHY - can be divided into traumatic and nontraumatic causes.

Traumatic plexopathy encompasses wide range of injury severities, with imaging assessing the extent of damage, guiding prognosis, and potential intervention.Nontraumatic plexopathy is diverse group of conditions, including neuritis caused by factors such as inflammation,compression,neoplastic disorders, both benign and malignant,infection.

-TRAUMATIC INJURIES

PATHOLOGIES : Preganglionic and postganglionic injuries

IMAGING FINDINGS: Nerve discontinuity and pseudomeningocele on MRI, thickening and increased signal intensity in Postganglionic injuries

Diagrammatic representation of Nerve injuries types in Fig15 .The nerve root avulsions, termed neurotmesis, can be divided into preganglionic and postganglionic categories with signs shown in fig16 helps in diagnosis.

Fig 15: Traumatic injury diagrammatic representation

Fig 16: Signs of preganglionic and postganglionic nerve injuries

Preganglionic injury consists of roots avulsion from the spinal cord .It includes pseudomeningocele, spinal cord edema shown in Fig17.Postganglionic injury includes focal caliber change of trunk, root and loss of fascicular architecture, neuroma, altered nerve signal intensity.Neuromas appear as oval lesions shown in Fig18, isointense on T1 and hyperintense on T2, with ill-defined borders and continuity with the parent nerve. T2 signal may be heterogeneous with strong enhancement. Although they can resemble peripheral nerve sheath tumors,history of trauma and parent nerve discontinuity is important for diagnosing end-bulb neuroma

Fig 17: Preganglionic injury with pseudomeningocele

Fig 18: Postganglionic injury with traumatic neuroma

Neonatal traumatic injuries:

Neonatal brachial plexus injuries occur in upto 0.5% of live births, with injury type depending on arm position during delivery. Erb-Duchenne palsy, the most common, affects C5 and C6 (sometimes C7), causing weakness in supraspinatus, infraspinatus, deltoid, and biceps muscles.Klumpke palsy, involving C8 and T1, leads to weakness in  hand's interosseous muscles and forearm and may be associated with Horner syndrome.Case of Birth injury with root avulsion shown in Fig19.Naraka classification of obstetric neonatal brachial injuries based on affected nerve root and clinical profile,helps to identify the types of injuries shown in Fig20

Fig 19: Birth plexus injury with pseudomeningocele

Fig 20: Naraka obstetric brachial plexus injuries

 -NON TRAUMATIC PLEXOPATHIES

 1.INFLAMMATORY /NEUROPATHIC CONDITIONS:

 PATHOLOGIES :Acute Brachial plexitis also called Parsonage-Turner syndrome

IMAGING FINDINGS:Thickening,Edema and enhancement of nerve roots on MRI,slight diffuse edema in surrounding muscles

Acute Brachial plexitis: Spontaneous brachial plexitis typically presents with acute-onset upper extremity pain,along with T2 hyperintensity,thickening,and variable enhancement of the brachial plexus components shown in Fig21. It may also show enlargement of affected shoulder girdle muscles, with enhancement and T2 hyperintensity, indicating signs of acute or subacute denervation.

Fig 21: Case of Inflammatory neuritis

2.COMPRESSIVE NEUROPATHIES:

PATHOLOGIES: Thoracic outlet syndrome, Compression of Brachial plexus,space-occupying vascular abnormalities such as pseudoaneurysm, arteriovenous fistula of subclavian, axillary, common carotid and vertebral arteries.The brachial plexus components can be affected at interscalene triangle, costoclavicular space,pectoralis minor space

IMAGING FINDINGS :Signal alteration and Thickening of Plexus structures on MRI

Case of Neoplastic mass in Fig22 and Case of Hematoma in Fig23 cause compression of brachial plexus with weakness and denervation atrophy of shoulder muscles.

Fig 22: Case of compressive neuropathy due to neoplastic mass

Fig 23: Case of compressive neuropathy due to hematoma in patient with post stenting of subclavian artery aneurysm

Case of Vertebro-vertebral fistula shown in Fig24 with sudden onset of right upper limb weakness due to tortuous perimedullary and paravertebral flow voids causing compressive radiculopathy.

Fig 24: Case of compressive radiculopathy due to vertebro-vertebral fistula

3.NEOPLASMS

PATHOLOGIES :Schwannomas,neurofibromas,benign and malignant nerve sheath tumors.

IMAGING FINDINGS:Lobulated solid lesions,Multiple Plexiform neurofibromas,Infiltration by surrounding structures .

Case of Neurofibroma in Fig25: A “target sign” of central T2 hypointensity and peripheral T2 hyperintensity, corresponds histologically to central area of collagen surrounded by myxomatous tissue

Fig 25: Case of Neurofibroma with target sign

Malignant lesions can either primarily arise within the brachial plexus or spread to brachial plexus secondarily. Primary malignant lesions involving the brachial plexus are predominately sarcomatous (low-grade sarcoma, radiation-induced sarcoma, osteosarcoma, Ewing Sarcoma, leiomyosarcoma, liposarcoma). In metastatic disease, the most common primary malignancies are breast, lung, lymphoma,head/neck cancer.

Case of lung adenocarcinoma in Fig26, secondarily involves brachial plexus ,causing nodular thickening via direct extension in the setting of Pancoast tumor involving the superior sulcus.

Fig 26: Case of Pancoast tumor causing compression with involvement of brachial plexus

Breast carcinoma ,lymphoma and head/neck malignancies usually involve the brachial plexus via metastatic regional lymphatic spread. Case of Breast carcinoma with metastases to brachial plexus in Fig27 causes motor and sensory loss of left upper limb. Spindle cell tumor in the left supraclavicular region in Fig28 cause compression with infiltration of trunks and cords.

Fig 27: Case of Carcinoma breast with involvement of brachial plexus

Fig 28: Case of spindle cell tumor with infiltration of brachial plexus

4.RADIATION PLEXOPATHY

IMAGING FINDINS: T2 hypointense thickening of the brachial plexus components, without focal mass, may occur following local radiation in context of prior malignancy. The time course is crucial for distinguishing radiation-induced plexopathy from recurrence or metastasis, as radiation-induced plexopathy typically develops between 5 and 30 months post-treatment shown in Fig29

Fig 29: Case of Radiation induced plexopathy in Carcinoma breast patient

5.INFECTIVE PLEXOPATHY:

Herpes zoster Plexopathy: Herpes zoster is the reactivation of latent varicella zoster virus. One of its complications is zoster-associated limb paresis.

IMAGING:Secondary denervation changes in shoulder girdle muscles and nerve T2 signal hyperintensity, followed by nerve enlargement shown in Fig30

Fig 30: Case of herpes plexitis