Small Vessel Pathology (Capillaries or Endoneurial Microvessels)
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Capillaries
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Endomysial Capillary: Normal
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ENDOMYSIAL CAPILLARIES
Capillary
Endothelial cell = E: Lumenal side of vessel wall
Pericyte = P: Several within basal lamina, outside of endothelial cell processes
Basal lamina: 1 to 3 Thin layers around outside of capillary
Capillary Structure
Basement membrane
Around & outside endothelial cell layer
May be homogeneous or layered
Contains pericytes (P)
Composition
Collagen IV
Laminin
Glycoproteins: Fibronectin, Nidogen-1, Nidogen-2 (Entactin)
Proteoglycans (as HSPG): Perlecan, Agrin
Thickening: Differential diagnosis
Fibroblasts
Not present
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Endothelial cells (E)
Surround lumen
Stains: Ulex Europaeus Agglutinin I (UEAI); CD31
Other markers: ADGRF5, BTNL9, VWF
Pericytes (P)
Location: Within basal lamina of vessel wall
Contractile
Frequency vs Endothelial cells: 1:10 to 1:100
Markers: PDGRFβ; NG2, Desmin, KCNJ8; ABCC9; CD13
Smooth muscle
Markers: Smooth muscle actin; PDGRFβ; CD13; NG2; CD146; Desmin
Histiocytes
Markers: CD163; CD206; LYVE1; F4/80; HAM56
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Muscle Capillaries: Features
Anatomy
- Adult: Normal
- Numbers: All muscle fibers have adjacent capillaries
- Orientation: Capillaries usually run along length of muscle fibers
- Child (< 2 years)
- Numbers: Many muscle fibers have no adjacent capillary
Plasticity
- Increased Capillary Numbers
- Muscle activity: Exercise; Electrical stimulation
- Denervation
- Anti-angiogenic thrombospondin-1 (TSP-1): Deletion
- Reduced Capillary Numbers
Endomysial Capillary Features: Stain & Molecular Analysis
Endothelial Cells |
Basement Membrane |
Immune |
H&E: Morphology
Ulex: Distribution;
#; Size; Stain intensity
ATPase pH 4.3: #+
Alkaline phosphatase: #+
NADH: + or -
Other markers: VWF, BTNL9, ADGRF5
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Morphology
H&E
GT/VvG
Ultrastructure
Molecular
Decorin/Col IV
PAS: + or -
Pericytes
PDGFRβ
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Humoral
C5b-9
Cellular
Acid phosphatase
HAM56
Cell involvement
Muscle: MHC I
Capillary: MxA
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Endomysial Capillaries: Normal
UEA I stain
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Endomysial capillaries: Normal
Normal number: Every muscle fiber has at least one adjacent capillary
Orientation: Run parallel to muscle fiber length; Cut in cross-section
UEA I stain
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All muscle fibers have at least one adjacent capillary
UEA I stain
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There are few or no capillaries immediately adjacent to the perimysium
UEA I stain
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Endomysial Capillaries: Reduced numbers
Some muscle fibers have no adjacent capillary
UEA I stain
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Endomysial Capillaries: Partial Denervation
UEA I stain
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Endomysial capillaries
Orientation: Abnormal; May be circumferential around muscle fibers (Above) cut in cross-section
Number: Increased; Every muscle fiber has several adjacent capillaries
UEA I stain
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Endomysial capillaries
Orientation: Normal
Number: Reduced or absent Endothelium (Ulex stain) in regions with small muscle fibers (Arrow)
Endothelium is lost but
basal lamina is still present
& may have
C5b-9 deposition
Size: Increased in regions neighboring muscle fiber atrophy
UEA I stain
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Endomysial Capillaries: Enlarged
UEA I stain
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UEA I stain
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Patient history: Cardiac failure & Interstitial lung disease
Muscle: Endomysial Capillary Vasculopathy
Muscle:
C5b-9 Deposits On Endomysial capillaries
Microvasculopathy
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Control Muscle
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Microvasculopathy: C
5b-9 Deposits on many endomysial capillaries
Muscle (Endomysial) Capillaries: Ultrastructure
Endomysial Capillary: Normal
Lumen: Patent
Endothelial cell processes: Form inner layers of capillary wall
Pericyte (White arrow): Around endothelial cell processes
Basal lamina: Thin
Endomysial Capillary: Normal
Lumen: Patent; Contains erythrocyte
Endothelial cell processes: Form inner layer of capillary wall
Pericyte: Not visible
Basal lamina (White arrow): Thin
Nucleus (Large; Upper right): Probably a muscle fiber nucleus
Endomysial Capillary: Normal
Lumen: Patent
Endothelial cell processes: Form inner layer of capillary wall
Pericyte: Not visible
Basal lamina (White arrow): Thin
Nucleus (Large): Neighbors capillary; May be a resident histiocyte
Endomysial Capillary: Basal lamina thick & homogeneous
Lumen: Patent
Endothelial cell processes: Form inner layer of capillary wall; Vesicles in cytoplasm
Basal lamina: Thick, Homogeneous; Contains a few small cell processes
Endomysial Capillary: Basal lamina thick & homogeneous
Lumen: Patent
Endothelial cell processes: Form inner layer of capillary wall; Vesicles in cytoplasm
Basal lamina: Thick, Homogeneous; Contains a few small cell processes
Endomysial Capillary: Basal lamina thick & homogeneous
Lumen: Patent
Endothelial cell processes: Form inner layer of capillary wall; Vesicles in cytoplasm
Basal lamina: Thick, Homogeneous; Contains a few small cell processes
Endomysial Capillary: Basal lamina thick & homogeneous
Lumen: Patent
Endothelial cell processes: Form inner layers of capillary wall
Basal lamina
Width: Thick
Structure: Homogeneous
Contains a few small cell processes
Outer edge: Irregular
From Robert E Schmidt
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Endomysial Capillary in Muscle
Lumen: Contains erythrocyte
Endothelial cell: contains large nucleus
Basal lamina: Mildly thick: Outer edge irregular
Endomysial Capillaries: Thick walls with Multilayered structure
Lumen: Patent; May contain erythrocyte (Above)
Endothelial cell processes: Thick; Form inner layers of capillary wall
Pericyte processes: Present within basal lamina layers
Basal lamina
Width: Thick
Structure: Multilayered; Varied around vessel circumference
Contains pericyte processes
Outer edge: Irregular
Fibrocyte processes (Arrows): Neighbor outer edge of capillary
Also see:
Systemic sclerosis, Endomysial capillaries
- Microvessel Properties
- Orientation
- Along nerve length
- Many oblique & transverse anastomoses
- Density
- 60 to 100/mm2
- Some reduction with increased age
- Sizes
- Larger than capillaries in other tissues
- Normal range: 5 to 22 μm; Mean 9 μm;
- May stain for
- Alkaline phosphatase
- UEAI lectin: Endothelial cells
- Scaffolding proteins: Link endothelial cell membranes to cytoplasmic components
- ZO-1 (TJP1)
- CLDN5
- Microvessel Components
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- Endothelial cells
- Number: ~ 4 to 5 per vessel cross-section
- Location: Single layer next to vessel lumen
- Borders
- Linked by: Tight junctions; Claudins & Adhesion molecules
- Component of: Blood-Nerve barrier
- No fenestrae
- Contain
- Weibel-Palade bodies: ? Produce Factor VIII-related antigen
- Pinocytotic vesicles
- Surrounded by: Pericytes & Basal lamina connective tissue
- Molecular
- Vessel specific (Endoneurial & Epineurial)
- CLDN5
- ESAM
- MPDZ
- CDH6: Adherens junctions; Large axons
- Specific for Endoneurial Microvessels
- Basement Membrane
- Composed of: Layers of
- Collagen
- Connective tissue
- Pericyte processes
- Pericytes
- Locations: May reside within basal lamina or around microvessel
- Processes: May neighbor, or surround, peripheral sides of endothelial cells
- May be: Resident histiocytes
- Smooth Muscle: Not generally present
- Blood-Nerve Barrier
Pathology & Ultrastructure
H&E stain
Endoneurial Microvessel (Arrow)
Orientation: Along length of nerve
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Endoneurial Microvessel Walls
Endothelial cells: Toward lumen
Pericytes (Arrows): Within, or outside, microvessel wall (Basal lamina)
Toluidine blue stain
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Endoneurial Microvessels: Near Normal
Endoneurial Microvessels
Lumen: Filled with RBCs
Endothelial cell with nucleus (Black arrow)
Neighbored around lumen by Endothelial cell processes
Pericyte (Gray arrow)
Endoneurial Microvessel: Surrounded by Pericyte processes
Endoneurial Microvessel
Lumen: Filled with RBC
Endothelial cell with nucleus
Neighbored around lumen by other Endothelial cell processes
Pericytes
Surround microvessel
Basal lamina: Surrounds microvessel & pericytes
Endoneurial Microvessel: Surrounded by Pericyte processes
Endoneurial Microvessel
Lumen: Contains 1 RBC
Endothelial cells: 2 nuclei are present
Neighbored around lumen by other Endothelial cell processes
Pericyte processes
Surround microvessel
Endoneurial Microvessels: "Closed"; Lumen is filled by endothelial cell processes
Endoneurial Microvessel, "Closed"
Lumen: None; Region is filled by endothelial cell processes
Endothelial cells: 1 nucleus is present
Neighbored in lumen by Endothelial cell processes
Pericyte processes: Surround endothelial cell processes
Basal lamina: Few thin layers of connective tissue incompletely surround vessel
Also see: HIEM
Endoneurial Microvessel, "Closed"
Lumen: None; Region is filled by endothelial cell processes
Endothelial cells: 1 nucleus is present
Pericyte processes: Surround endothelial cell processes
Basal lamina: Increased layers of connective tissue surround vessel
Endoneurial Microvessel, "Closed"; Surrounding cells
Lumen: None; Region is filled by endothelial cell processes
Endothelial cells: 2 nuclei are present
Pericyte processes: Surround endothelial cell processes
Basal lamina: Few thin layers of connective tissue incompletely surround vessel
Surounding cells: Increased cellularity aroound endoneurial microvessel
Endoneurial Microvessel Endothelium: Increased numbers & processes of endothelial cells
Lumen: Present
Endothelial cells & processes: Multiple
Pericyte processes: Surround endothelial cells
Basal lamina: Layers of connective tissue around vessel moderately increased
Disease: HIEM
Endomysial & Endoneurial Capillaries: Thick Walls
Capillary Walls Thick: Differential diagnosis
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Endoneurial Microvessel: Thick Basal Lamina
Lumen: Present
Endothelial cells & processes: Present
Pericyte processes: Surround endothelial cell layer
Basal lamina: Increased connective tissue layers
Patient Clinical: No diabetes, Motor-sensory axonal PN
Endoneurial Microvessel: Thick Basal Lamina
Lumen: Present
Endothelial cells & processes: Present
Pericyte processes: Surround endothelial cell layer
Basal lamina: Increased connective tissue layers
Patient Clinical: No diabetes, Motor-sensory axonal PN
From: Chunyu Cai
Endoneurial microvessel (Diabetes)
Basal lamina: Thick; Multilayered (Arrow)
Endothelial cell: Dark-stained cytoplasm
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Ultrastructure: From Robert E Schmidt
Diabetes
Endoneurial Microvessel
Basal lamina: Thick Contains: Multiple thin layers
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Endoneurial Microvessel: Basal Lamina Fragmentation (HIEM)
Endoneurial Microvessel
Basal lamina: Rarified & Wide, especially outer layers
Lumen: Present
Endothelial cells & processes: Present
Pericyte processes: Not prominent
Basal lamina (Arrow)
Layers of connective tissue around vessel: Moderately increased
Outer layers of connective tissue: Pale & Disorganized
Endoneurial Microvessel: Basal Lamina Disorganized (HIEM)
Endoneurial Microvessel
Basal lamina: Rarified & Wide, especially outer layers
Lumen: Present
Endothelial cells & processes: Present
Pericyte processes: Not prominent
Basal lamina (Arrow)
Layers of connective tissue around vessel: Moderately increased
Outer layers of connective tissue: Pale & Disorganized
Endoneurial microvessels
Basal lamina: Thick; Homogeneous (Arrows)
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Endoneurial microvessel Basal lamina: Normal (Arrow)
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Endoneurial Microvessels: Walls have varied thickness
Humoral Immune Endoneurial Microvasculopathy (HIEM)
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Associated Clinical Syndrome
- Confluent Asymmetric Neuropathy (HIEM)
C5b-9 stain
HIEM Nerve
C5b-9 Stains Most Endoneurial Microvessels
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Disease Control Nerve
C5b-9 Stains Perineurium & Epineurial vessels but not Endoneurial microvessels
C5b-9 stain
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HIEM Nerve
C5b-9 Stains Endoneurial Microvessels
C5b-9 stain
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C5b-9 stain
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Endoneurial Microvasculopathy
HIEM: C5b-9 stains Endoneurial microvessels
C5b-9 stain
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Disease Control Nerve
C5b-9 does not stain Endoneurial microvessels
C5b-9 stain
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C5b-9 (Green) + UEAI (Red) stain
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HIEM: C5b-9 stain (Green) around Endoneurial Microvessel endothelium (Red)
C5b-9 (Green) + UEAI (Red) stain
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C5b-9 (Green) + UEAI (Red) stain
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Toluidine blue stain
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Endoneurial Microvessel Pathology
Vessel size: Normal or Large
Vessel wall: Thick
Endothelial cells: Large
Basal lamina: Multi-layered; Fragmented
See: Ultrastructure
Toluidine blue stain
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HIEM: Endoneurial Microvessel Ultrastructural Pathology
Endoneurial Microvessel
Basal lamina: Fragmented, Rarified & Wide, especially outer layers
Lumen: Present
Endothelial cells & processes: Present
Pericyte processes: Not prominent
Basal lamina (Arrow)
Layers of connective tissue around vessel: Moderately increased
Outer layers of connective tissue: Pale & Disorganized
Endoneurial Microvessel
Basal lamina: Fragmented, Rarified & Wide, especially outer layers
Lumen: Present
Endothelial cells & processes: Present
Pericyte processes: Not prominent
Basal lamina (Arrow)
Layers of connective tissue around vessel: Moderately increased
Outer layers of connective tissue: Pale & Disorganized
Endoneurial Microvessel
Basal lamina: Rarified & Wide, especially outer layers
Lumen: Absent; Filled by endothelial cell processes
Endothelial cells & processes: Present
Pericyte processes: Not prominent
Basal lamina (Arrow)
Layers of connective tissue around vessel: Moderately increased
Outer layers of connective tissue: Pale & Disorganized
From R Schmidt
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HIEM Microvessel
Endothelial cells: Multiple, Large
Pericyte: Processes surround microvessel
Basal lamina: Disorganized around outside of vessel
From R Schmidt
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HIEM Microvessel
"Closed": No lumen
Endothelial cells: Multiple, Large
Pericyte (Arrow): Process partially surrounds microvessel
Basal lamina: Connective tissue layers surround most of the vessel
HIEM: Nerve anatomic pathology
H&E stain
HIEM nerve: No lymphocytic inflammation
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VvG stain
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HIEM: Differential fascicular involvement
Myelinated axon loss: Varied (Above)
Endoneurial ATPase stain: Varied (Below)
ATPase pH 4.3 stain
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Toluidine blue stain
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HIEM sural nerve
Moderate loss of large & small myelinated axons
Regeneration: Clusters of small myelinated axons
Endoneurial microvessels
Basal lamina: Thick
Endothelial cells: Large
Toluidine blue stain
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Toluidine blue stain
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HIEM sural nerve
Large & small myelinated axons: Severe loss (Above)
Small unmyelinated axons: Relatively preserved (Below)
Neurofilament stain
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Control sural nerve
Large & Small axons are present
Neurofilament stain
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References
1. Acta Neuropathol 2000;100:445-450
2. Am J Physiol Heart Circ Physiol 2016 Jul 1
3. J Peripher Nerv Syst 2019;24:195-206
7/25/2024