Mri brachial plexus radiology 1. Normal anatomy 2. relevant pathology and it's imaging findings 3.normal mri appearance included images

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MRI of the Brachial Plexus: Comprehensive Radiology Review

1. Normal Anatomy

Overview

The brachial plexus is a somatic nerve plexus formed by the anterior rami of C5, C6, C7, C8, and most of T1. It originates in the neck, passes laterally and inferiorly over the first rib, and enters the axilla. Its organization follows the mnemonic: Roots - Trunks - Divisions - Cords - Branches (Randy Travis Drinks Cold Beer).

Brachial plexus anatomy diagram showing roots (C5-T1), trunks, divisions, and cords with scalene muscles and sympathetic ganglia

Gray's Anatomy for Students - Brachial plexus: roots (anterior rami C5-T1), trunks, divisions, cords, and relationship to scalene muscles and sympathetic chain

Component	Details
Roots	Anterior rami C5-T1; pass between anterior and middle scalene muscles
Trunks	Superior (C5+C6), Middle (C7), Inferior (C8+T1); pass over rib I into the axilla
Divisions	Each trunk splits into anterior + posterior divisions (6 total) at the clavicular level
Cords	Lateral (anterior divisions of superior + middle), Medial (anterior division of inferior), Posterior (all three posterior divisions); named by relationship to the axillary artery
Terminal branches	Musculocutaneous, median, ulnar, radial, and axillary nerves

Key spatial relationships:

Roots and trunks lie in the posterior triangle of the neck, posterior to the subclavian artery, between anterior and middle scalene muscles (interscalene space)
At the level of the clavicle - the costoclavicular space
Infraclavicular - the retropectoralis minor space (beneath the pectoralis minor muscle)
Cords surround the axillary artery in the axilla

MRI Protocol

The normal medial-to-superior orientation of the plexus makes standard axial/coronal/sagittal sequences difficult to interpret, because the nerve course runs obliquely. Standard protocol includes:

Oblique coronal T2 fat-suppressed - best plane for overall plexus visualization; allows bilateral comparison
Oblique sagittal T2 - best for evaluating individual nerve segments and foraminal exit zones
Axial T1 / T2 - good for relationship to vascular structures
3D T2/STIR (heavy T2 myelographic sequences) - critical for nerve root visualization and detecting meningoceles
T1 post-gadolinium fat-sat - for detecting neoplastic infiltration and enhancement
Field strength: 3T preferred (better SNR), though 1.5T is adequate

Normal MRI Signal Characteristics

On standard MRI, normal brachial plexus nerves appear as:

T1-weighted: intermediate signal, similar to muscle; individual roots appear as small oval/round structures within the neural foramina surrounded by epidural fat (which gives bright T1 signal, providing natural contrast)
T2-weighted: mildly hyperintense compared to muscle; slightly brighter due to the endoneurial fluid content - but LESS bright than surrounding fat or CSF
STIR / fat-suppressed T2: nerves are intermediate-to-slightly hyperintense; fat suppression removes background fat signal and makes nerves easier to delineate

The critical principle: normal nerves should NOT show bright T2 signal - significant T2 hyperintensity indicates edema or pathology.

Coronal MRI brachial plexus showing C5, C6, C7, C8 roots and superior/middle trunks labeled with color overlay

Coronal fat-suppressed MRI showing labeled brachial plexus roots (C5-C8) and trunks emerging from the intervertebral foramina

Oblique sagittal MRI with labeled brachial plexus trunks (superior, middle, inferior) and subclavian artery at the level of the first rib

Oblique sagittal MRI at the costoclavicular level showing superior, middle and inferior trunks in relation to the subclavian artery

Coronal-oblique MRI brachial plexus with labeled cervical levels C5-T1, axilla, shoulder, and thoracic inlet structures

Labeled T1 coronal MRI demonstrating the full extent of the brachial plexus from cervical exit foramina (C5-T1) through the thoracic inlet (K1) to the axillary region (K2, K3)

Normal Appearance - Segment by Segment

Segment	MRI Landmark	Appearance
Nerve roots (preganglionic)	Within neural foramina	Oval low-signal structures surrounded by bright epidural fat on T1
Dorsal root ganglion	Neural foramen	Slightly enlarged rounded structure, may show faint T2 brightness
Postganglionic roots	Interscalene triangle	Thin linear structures between anterior and middle scalene muscles
Trunks	Between scalene muscles and clavicle	Round/oval structures, isointense to slightly hyperintense on T2-STIR
Divisions	At the clavicle	Flat, ribbon-like structures; divided into anterior and posterior
Cords	Infraclavicular, around axillary artery	Bundle surrounding the axillary artery; named by position relative to it

2. Relevant Pathology and Imaging Findings

A. Traumatic Brachial Plexus Injury

Traumatic injury is the most common indication for brachial plexus MRI, typically from high-velocity traction (motorcycle accidents, birth trauma). Injuries are classified as preganglionic (proximal to dorsal root ganglion, not repairable by nerve grafting) vs postganglionic (distal, potentially repairable).

75% of clinical brachial plexus injuries involve root avulsion from the cord; 25% are confined to the distal plexus - Grainger & Allison's Diagnostic Radiology

Preganglionic (Root Avulsion) - MRI Findings:

Traumatic pseudomeningocele - CSF-filled outpouching extending through the torn dural sleeve into the paraspinal region; appears as a bright T2 / dark T1 fluid collection extending from the foramen (PATHOGNOMONIC of avulsion)
Absent intradural nerve root - the normal linear filling defect within the hyperintense CSF is absent on myelographic T2 sequences
Cord edema - diffuse T2 hyperintensity of the spinal cord; must not be confused with direct cord injury
Denervation changes in paraspinal muscles - multifidus and semispinalis capitis atrophy (these receive dorsal ramus branches from the avulsed roots)

Sagittal T2 MRI showing diffuse cord edema due to multiple nerve root avulsions at cervical levels

Sagittal T2 MRI - diffuse cervical cord edema secondary to multiple nerve root avulsions. Grainger & Allison's Diagnostic Radiology

Coronal T2 myelogram-sequence showing brachial plexus avulsion at C8 and T1 with traumatic meningoceles (white arrows) on the left

Coronal T2 "myelogram" sequence - brachial plexus avulsion at C8 and T1 on the left, with traumatic meningoceles (arrows). Grainger & Allison's Diagnostic Radiology

Coronal and sagittal T2 MRI showing pseudomeningocele at C6-C7 right side with denervation atrophy of multifidus/semispinalis

T2 sagittal and axial MRI: T2-hyperintense pseudomeningocele in right C6-C7 neural foramen (yellow arrows) from preganglionic nerve root avulsion, with atrophic right multifidus (blue arrows). Imaging Anatomy: Bones, Joints, Vessels and Nerves

Postganglionic Injury - MRI Findings:

Nerve enlargement with T2 hyperintensity (edema/neuritis)
Disruption or discontinuity of nerve fibers on high-resolution sequences
Intact nerve roots visible on myelographic sequences (distinguishes from preganglionic)
Surrounding hematoma / edema in surrounding soft tissues
Late changes: fatty replacement and atrophy of denervated muscles

Coronal and sagittal MRI showing large pseudomeningocele (C6-C8, T1) with cord atrophy and denervation of subscapularis, supraspinatus, infraspinatus, serratus anterior

Coronal T2 (a) and T1 (b) MRI showing large pseudomeningocele from C6-T1 avulsion with brachial cord atrophy (green arrow); axial views (c,d) show denervation of left subscapularis, supraspinatus, infraspinatus, and serratus anterior. Imaging Anatomy: Bones, Joints, Vessels and Nerves

B. Neoplastic Plexopathy

Metastatic / Tumor Infiltration

Common primary tumors: breast, lung (especially Pancoast), lymphoma, sarcoma.

MRI findings:

A mass lesion adjacent to or engulfing brachial plexus elements
T2 hyperintensity and nerve enlargement in involved segments
Avid contrast enhancement - mass-like or infiltrative pattern
May show epidural extension (very important surgical consideration)
MRI sensitivity for detecting tumor infiltration: 96%, specificity 95% - Bradley and Daroff's Neurology in Clinical Practice
Typically involves the lower plexus (C8-T1) for Pancoast tumors (weakness of intrinsic hand muscles, 4th and 5th digit paresthesias, Horner syndrome)

Pancoast tumor (superior sulcus tumor): apical lung mass on chest radiograph; MRI demonstrates invasion of lower plexus roots, first rib, vertebral body, and subclavian vessels.

C. Radiation-Induced Plexopathy

Occurs as a delayed complication (3 months to 26 years; mean ~6 years) following radiotherapy, most often for breast cancer or lung cancer.

Mechanism: ischemic insult to vasa nervorum causing endoneural/perineural fibrosis + direct myelin/axon damage.

MRI findings:

Diffuse thickening of plexus elements within the radiation field
T2 signal increase - moderate, diffuse rather than focal
No discrete mass (helps distinguish from metastatic plexopathy)
Fibrosis may produce low T2 signal in chronic cases
On Gadolinium: may show enhancement in acute/subacute phase
Surrounding muscles may show post-radiation fatty atrophy

Clinical pearl: if there is NO identifiable mass on MRI and appropriate history + clinical signs are present, MRI reliably distinguishes radiation plexopathy from metastatic recurrence. - Grainger & Allison's Diagnostic Radiology

D. Thoracic Outlet Syndrome (TOS)

Compression of the brachial plexus (neurogenic TOS) within one of three anatomic spaces: interscalene triangle, costoclavicular space, or subcoracoid (pectoralis minor) space.

Causes: cervical rib, fibrous band from short cervical rib to first rib (angulates the lower trunk), scalene anomalies, clavicular/first rib fracture malunion.

MRI findings:

Dynamic MRI (provocative positions: arm abduction, external rotation) most useful
Cervical rib or elongated C7 transverse process on coronal sequences
Fibrous band stretching/angulating the inferior trunk
Neural compression visible at the scalene triangle or costoclavicular space
Associated subclavian/axillary vessel compression may be seen

Coronal image showing SA = subclavian artery and SV = subclavian vein in relation to plexus:

Coronal MRI of the brachial plexus showing subclavian artery (SA) and subclavian vein (SV) labeled with yellow arrows

Coronal fat-suppressed MRI: subclavian artery (SA) and subclavian vein (SV) in relation to brachial plexus structures. Applied Radiology

E. Inflammatory Plexopathy (Parsonage-Turner Syndrome / Neuralgic Amyotrophy)

Idiopathic or post-infectious/post-vaccination immune-mediated plexitis.

MRI findings:

T2 hyperintensity and mild enlargement of affected nerves - often patchy, multifocal
May involve the suprascapular nerve, long thoracic nerve, or multiple cord levels
Denervation edema in affected muscles (T2 bright, T1 dark initially)
Late: fatty atrophy of denervated muscles (T1 bright)
Often normal early in the course - MRI changes may lag symptoms by several weeks
Magnetic resonance neurography (MRN) is the most sensitive technique

F. Peripheral Nerve Sheath Tumors

Schwannoma and neurofibroma are the most common benign peripheral nerve tumors. Neurofibromas are strongly associated with NF1.

MRI findings:

Fusiform mass along the course of a nerve (spindle-shaped)
T1: isointense to muscle
T2: markedly hyperintense ("target sign" - central low T2 with peripheral high T2 - characteristic of neurofibroma)
Gadolinium enhancement: avid, usually homogeneous for schwannoma; heterogeneous for large neurofibromas
Malignant peripheral nerve sheath tumors (MPNST): irregular margins, rapid growth, heterogeneous enhancement, perineural spread, satellite nodules

Summary Table: Pathology at a Glance

Pathology	Key MRI Features	Location
Root avulsion (preganglionic)	Pseudomeningocele, absent root, cord edema, paraspinal denervation	Foraminal / intradural
Postganglionic injury	Nerve T2 hyperintensity, enlargement, late atrophy	Interscalene to infraclavicular
Metastatic plexopathy	Mass + nerve enhancement, ± epidural extension	Often lower plexus (C8-T1)
Radiation plexopathy	Diffuse thickening, no mass, T2 increase in field	Within radiation field
TOS	Dynamic compression, cervical rib/fibrous band	Interscalene / costoclavicular
Parsonage-Turner	Patchy T2 hyperintensity, muscle denervation	Variable, often upper plexus
Schwannoma	Fusiform nerve mass, avid T2 signal, enhancement	Along any segment
Neurofibroma	Target sign on T2, fusiform, associated NF1	Along any segment

3. Normal MRI Appearance - Summary

On T1:

Roots surrounded by bright epidural fat within foramina (natural contrast)
Trunks and cords: round/oval structures, isointense to muscle
Scalene muscles provide easily recognizable landmarks

On T2/STIR fat-suppressed:

Nerves are mildly hyperintense relative to muscle
Clearly distinguishable from surrounding fat (which is suppressed)
Normal nerves should be smooth, symmetrical in caliber, and without focal T2 bright signal

Key structures to assess on every brachial plexus MRI:

Nerve root exit foramina (C5-T1) - patent, no compression
Interscalene triangle - scalene muscles normal, no fibrous bands
Costoclavicular space - no cervical rib or clavicular deformity
Pectoralis minor space - normal
Axillary artery and subclavian vessels - no vascular compression
Paravertebral/paraspinal muscles - symmetric, no denervation changes
Lung apex - exclude Pancoast tumor
Cervical spine - disc herniations, osteophytes, cord changes

Sources:

Grainger & Allison's Diagnostic Radiology, Block 10 & 12 (Brachial Plexus Injury; Radiation Plexopathy)
Imaging Anatomy: Bones, Joints, Vessels and Nerves, Block 2 (Ventral Rami, Upper Trunk, Divisions)
Gray's Anatomy for Students, Block 4-5 (Brachial Plexus)
Bradley and Daroff's Neurology in Clinical Practice, Block 27 & 6 (Plexopathies, Cancer)
Vijayasarathi A, Chokshi FH. "MRI of the brachial plexus: A practical review." Applied Radiology, 2016.

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