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Impaired Axon Regeneration

Location: May be proximal to, but near, region of nerve damage
No structural neuroma
Posterior Interosseus Nerve

Axons   Ultrastructure Myelin pathology Nerve morphology   Endoneurium   Perineurium Schwann cells   Büngner bands

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H&E stain

Nerve Morphology
  Endoneurial Edema

Gomori trichrome stain

Nerve Morphology
  Endoneurial Edema
  Loss of myelinated axons

VvG stain

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H&E stain

Nerve Morphology
  Endoneurial Edema

Gomori trichrome stain

Nerve Morphology
  Endoneurial Edema
  Abnormal myelin staining
    Bleb (Yellow arrow)
    Pale myelin staining (Black arrow)
    Ovoid-like structure (Orange arrow)

Gomori trichrome stain

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VvG stain

Nerve Morphology
  Loss of myelinated axons
  Abnormal myelin
    Pale stained myelin sheaths (Arrow)

VvG stain

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Myelin Sheaths
  Few remaining sheaths co-stain for MBP & P0

P0 green; MBP red

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Acid phosphatase stain

Histiocytes
  Small
  Scattered in endomysium

Acid phosphatase stain

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ATPase pH 4.3 stain

Endoneurium
  Patchy ATPase staining

ATPase pH 4.3 stain

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Perineurium: No neuroma formation
  EMA (Green)
    Stains only perineurium surrounding fascicles
    No endoneurial staining
  Compare to: Neuroma

P0 red; Epithelial membrane antigen (EMA) green

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NCAM stain

Non-myelinating Schwann cells
  Diffuse distribution in endoneurium
NCAM co-stains some myelin sheaths (Arrow)

NCAM stain

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NCAM green; P0 red

Myelin Sheaths (Red): Few; Scattered
Schwann cells/Büngner bands (Green): No de-differentiation; No co-staining for NCAM & P0

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From: R Schmidt

Büngner bands
  Interdigitated Schwann cellprocesses
    Surrounded by basal lamina
    No associated axons

From: R Schmidt

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From: R Schmidt

Schwann cells with inclusions
  Myelin remnants
  Pi granules

From: R Schmidt

Schwann cells with inclusions
  Myelin remnants
  Pi granules

From: R Schmidt

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Neurofilament stain

Clusters of large & small axons

Neurofilament stain

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Large axons: Many (Green) with no surrounding P0-stained myelin (Arrow)

Neurofilament green; P0 red

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Large axons: Many with no (Green) surrounding, or mild (Arrow; Yellow) NCAM+ Schwann cells

Neurofilament green; NCAM red

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Minor, or No, GAP43 staining of axons (Green)   See: Positive control in neuroma Neurofilament green; GAP43 red

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From: R Schmidt

Swollen Axon
  Size: Up to 8 μM
  Contain: Mostly tubulovesicular material
  Surrounded by
    Schwann cell processes
    No myelin

From: R Schmidt

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From: R Schmidt

Swollen Axons
  Size: Up to 12 μM
  Contain: Mostly tubulovesicular material, large
  Surrounded by
    Schwann cell nuclei, basal lamina & few small processes
    No myelin

From: R Schmidt

Swollen axon
  Contains various sizes of tubulo-vesicular material
  Compare to: Axons in & around neuroma

From: R Schmidt

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From: R Schmidt

Swollen Axon
  Size: Up to 10 μM
  Contains: Mostly tubulovesicular material
  Surrounded by
    Many small Schwann cell processes & Basal lamina
    No myelin

From: R Schmidt

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From: R Schmidt

Swollen Axon
  Size: Up to 10 μM
  Contains: Mostly tubulovesicular material
  Surrounded by
    Many small Schwann cell processes, large SC process with dark inclusion, SC nucleus & Basal lamina
    No myelin

From: R Schmidt

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From: R Schmidt

Swollen Axon
  Size: Up to 10 μM
  Contains: Mostly tubulovesicular material
  Surrounded by
    Small Schwann cell processes in some areas, large SC process filled with Pi granules & Basal lamina
    No myelin

From: R Schmidt

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From: R Schmidt

Swollen Axon
  Size: Up to 10 μM
  Contains: Mostly tubulovesicular material
  Surrounded by
    Multiple Schwann cell processes with various components & SC nucleus on one side
    Few smal SC process on other side
    Sc Basal lamina
    No myelin

From: R Schmidt

From: R Schmidt

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From: R Schmidt

Swollen Axon
  Size: Up to 10 μM
  Contains: Mostly tubulovesicular material
  Surrounded by
    Several Schwann cell processes with various components & SC nuclei on bottom
    Few small SC process on top
    SC Basal lamina
    No myelin

From: R Schmidt

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From: R Schmidt

Intermediate-sized axon Axon
  Size: Up to 6 μM
  Contains: Large tubulovesicular material
  Surrounded by
    Multiple Schwann cell processes
    No myelin

From: R Schmidt

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From: R Schmidt

Intermediate-sized axon Axon
  Size: Up to 6 μM
  Contains: Large tubulovesicular material
  Surrounded by
    Multiple large & small Schwann cell processes
    No myelin

From: R Schmidt

From: R Schmidt

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From: R Schmidt

Intermediate-sized axon Axon
  Size: Up to 6 μM
  Contains: Large tubulovesicular material
  Surrounded by
    Multiple large & small Schwann cell processes
    No myelin

From: R Schmidt

From: R Schmidt

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5/27/2025