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Brachial Plexus: Preganglionic vs Postganglionic

Fellowship-level neuroradiology teaching by E. Brooke Schrickel, MD. Open this topic in the interactive reading room →

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Core clinical idea

The plexus read turns on one divide: preganglionic (root avulsion at the cord — a different surgical problem) vs postganglionic (along trunks/cords/branches). Win it at protocol: cover C4-T2, use 3D T2 to kill CSF pulsation and see rootlets/DRG, key contrast to indication, and don't be fooled by magic angle.

Bottom line

Settle preganglionic vs postganglionic with the right protocol, then localize by fat effacement and denervation pattern — and don't let magic angle fool you.

Core workstation questions

  • Is this preganglionic (avulsion: CSF signal, pseudomeningocele, absent rootlets) or postganglionic?
  • Did I cover C4-T2, and can I see the rootlets/DRG (3D T2)? If not, is the preganglionic segment non-diagnostic?
  • Is the surrounding plexus fat effaced; is there infiltration/displacement?
  • What's the muscle denervation pattern, and which level does it localize?
  • Is suspicious T2 signal real or magic angle — does it confirm on a second sequence/plane?
  • Is there an underlying mass, node, or lung/mediastinal lesion driving this?

What changes reporting / management

  • In the report it is often clearer and more clinically useful to localize disease to the SUPRACLAVICULAR vs INFRACLAVICULAR brachial plexus rather than only roots/trunks/divisions/cords — supraclavicular ≈ roots and trunks (at/above the clavicle), infraclavicular ≈ cords and terminal branches (below the clavicle, toward the axilla). It maps to the surgical approach and is easier for the clinician to act on.
  • Image C4 through T2 every time to capture prefixed (C4-C8) and postfixed (C6-T2) variants.
  • Contrast fork: without contrast for trauma/avulsion and radiculopathy; with contrast for tumor/radiation neuritis, infection, Parsonage-Turner, NF1, polyneuropathy, thoracic outlet.
  • Use 3D T2 (SPACE/CUBE) for the preganglionic segment to suppress CSF pulsation and resolve ventral/dorsal rootlets and DRG; coronal T1 + coronal T2 fat-sat (Dixon) for the postganglionic plexus.
  • Avulsion = CSF-intensity signal at the foramen, pseudomeningocele, possible contralateral cord displacement, absent rootlets in the pouch; report level and rootlet presence because avulsion vs postganglionic rupture routes the surgery.
  • Prioritize C7-T1 in trauma (most-injured, most persistent pain); map muscle denervation (acute edema/enhancement, chronic atrophy/fatty change) back to the level.
  • Always sweep for the cause and its company: lymphadenopathy, mediastinal/lung (superior sulcus/Pancoast) mass, incidental neoplasm.
  • If rootlets can't be resolved, state the preganglionic segment is non-diagnostic rather than implying normal.

Practical traps

  • Magic angle: spurious T2/STIR fat-sat hyperintensity where the plexus runs near ~55 degrees to B0; worst on conventional spin echo, minimized on gradient echo — confirm on a second sequence/plane.
  • Narrow FOV clipping a prefixed/postfixed contributing root.
  • Tunnel vision on the plexus and missing the underlying mass/node/lung lesion.
  • Calling a degraded preganglionic study 'normal' when CSF pulsation obscured the rootlets.

Teaching pearls

  • Cover C4-T2 — prefixed and postfixed plexuses will clip a narrow FOV.
  • If you can't see the rootlets, you can't exclude avulsion — say so.
  • Avulsion vs postganglionic rupture is a different operation — that distinction is the read.
  • Fat effacement around the plexus is the tell; denervation pattern localizes the level.
  • Plexus signal at ~55 degrees to B0 is magic angle until a second sequence proves otherwise.
  • When precise root/trunk/cord localization is hard, describe plexus disease by supraclavicular vs infraclavicular level — it is still clinically actionable.

Teaching visuals

Practical Brachial Plexus Imaging5-tier organization (C5–T1) — schematic, conceptualROOTSReallyTRUNKSTiredDIVISIONSDrinkCORDSColdBRANCHESBeerC5C6C7C8T1UpperMiddleLowerantpostantpostantpostLateralPosteriorMedial(named vs. axillary artery)MusculocutaneousAxillaryRadialMedianUlnarImaging discriminator: where is the lesion vs. the dorsal root ganglion (DRG)?DRG sits in/near the neural foramen — it is the dividing line.PREGANGLIONIC (root avulsion)Lesion medial to the DRG — at/near the cord.Signs: pseudomeningocele, absent/displaced rootlets,cord signal change, denervation of paraspinals.NOT surgically repairable (graft requires a stump).POSTGANGLIONICLesion distal to the DRG — trunks/cords/branches.Signs: nerve thickening, T2 hyperintensity, scarring/ neuroma; foramen & thecal sac intact.Potentially repairable (graft / nerve transfer).Takeaway: pre- vs. post-ganglionic changes the surgery — find the DRG, then localize the lesion to it.
Brachial Plexus 5-Tier Schematic & Pre- vs Post-Ganglionic Injury

Source lectures

  • Practical Brachial Plexus Imaging

Educational material for radiology residents and neuroradiology fellows. Nothing here drives individual patient care, and it contains no patient data.