Perineuritis

PERINEURIUM

Perineurium: Disorders

Perineurium
- Normal
- Thin
- Thick
Damage & Abnormal structure
- Trauma
- Minifasciculation
- Neuroma
Calcification
Inflammation & Immune
- Perineuritis
- Subperineurial edema
- Spanish toxic oil
- Leprosy: "Onion-skinning"
- Other: Cryoglobulinemia; Sarcoid; Lyme; Lymphoma
Inclusions
- Fabry's
- Xanthomatous neuropathy
Neoplasm & Proliferation
- Perineurioma
- Perineuriosis (Proliferation of perineurial cells in endoneurium)
Also see: Perineurium components

Perineurium: Normal

Toluidine blue stain

Perineurium
Structure: Lamellar
Fewer fascicles in distal, smaller nerves
Outer layers may merge with epineurial connective tissue
Location: Surrounds all peripheral nerve fascicles
Cells
Basal lamina: Surrounds perineurial cells; Thicker than Schwann cell basal lamina
Cytoplasm contents
Filaments
Pinocytic vesicles: More in outer perineurial layers
Tight junctions: Link adjacent perineurial cells; More in inner perineurial layers
Origin: May be endoneurial fibroblasts
Molecular
Stained by: C_5b-9 antibodies
Contains: Collagens I & III
Function
Part of Blood-Nerve barrier
Regulates endoneurial melieu

Toluidine blue stain

Toluidine blue stain

VvG stain

Vessel within Perineurium

Toluidine blue stain

Perineurium: Thin

Perineurium: Thin & Narrow

Toluidine blue stain

Perineurium: Indistinct connective tissue layers

Toluidine blue stain

Perineurium: Narrow; Few fibrils

VvG stain

Perineurium: Wide & Thickened

Toluidine blue stain

Widened Perineurium: Increased numbers of connective tissue layers

Toluidine blue stain

Widened Perineurium: Perineurial cells often have multiple, small round, pinocytic vesicles

C_5b-9 stain

Widened Perineurium: Less prominent on histochemical stains

Widened Perineurium: Little acid phosphatase stain in contrast to perineuritis

C_5b-9 stain

Widened Perineurium: C_5b-9 stain is dark & wide

Perineuritis ¹

Anatomic Pattern
Axon involvement
Differential fascicular
Wallerian degeneration
Connective tissue
Inflammation
Perineurial Damage
Behçet
Vessels
Endoneurial inflammmation
Epineurial

Perineuritis: Anatomic Pattern in Nerve
General: Varied involvement among fascicles
Perineurial Connective Tissue Damage
Several fascicles with perineurial acid phosphatase staining (Arrows)
Wallerian degeneration with scattered Histiocytes (Larger fascicle; Right)

Acid phosphatase stain

Perineurium: Structural Damage, Varied patterns

Gomori trichrome stain
Perineurium
Widened around fascicle
Some areas are pale

Gomori trichrome stain
Perineurium
Widened around fascicle
Some areas are more dense or dark-stained

H&E stain

H&E stain
Perineuritis
Perineurium (arrow):
Rarified & Thickened
Inflammation: Epineurium

H&E stain
Another fascicle, Same nerve
Perineurium (arrow)
Normal staining
Moderately Thick
No inflammation

Perineurium
Widened around fascicle
Some areas are light- or dark-stained
Cellularity: Increased
Endoneurium
Microvessels: Large; Darker stained
Axons: Reduced numbers

H&E stain

VvG stain

H&E stain

Perineuritis: Perineurial pathology
Connective tissue staining
Increased (Above)
Reduced (Below)

Gomori trichrome stain

Toluidine blue stain

Toluidine blue stain

Perineuritis: Perineurial structure is Abnormal

Layers: Widened or Condensed (Above)
Cellularity within layers is increased (Below)

Toluidine blue stain

Perineuritis: Inflammation

H&E stain

H&E stain

Perineuritis: Increased histiocytic cellularity in & near perineurium

Acid phosphatase stain

Acid phosphatase stain

Perineuritis: Histiocytic cells
In perineurium & endoneurium
Confluent red stained histiocytes, mainly in perineurium
Endoneurial cells: May reflect Wallerian degeneration

Perineuritis: Cells around Endoneurial microvessels

Perineuritis: Abnormal Epineurial & Endoneurial vessels

Epineurial Vessels
Artery, Large: Damaged structure; Interrupted internal fibril layer
Smaller vessel (Botton right): Perivascular inflammatory cells