Definition: Granuloma annulare (GA) is a benign inflammatory, self-limiting granulomatous dermatoses that is seen in both adults and children . Females are more commonly affected than males. The lesions may involve skin and/or subcutaneous tissue. The etiology of GA is unknown.

Synopsis

 palisading granuloma located in the superficial and mid dermis.

• central zone of altered collagen surrounded by fibrohistiocytic cells and spindle cells focally radiating around the periphery
• centrally altered collagen (so-called necrobiosis) surrounded by cells having fibrohistiocytic morphology
• spindle cells radiating around the periphery of the zone of altered collagen
• areas of necrobiosis surrounded by peripheral rim of histiocytes and lymphocytes.
• +/- multinucleated giant cells
• intervening areas of dermis between the necrobiotic granulomas is normal.
• central necrobiotic area contains abundant connective tissue mucins which is lightly basophilic in apperance(Staining: colloidal iron, alcian blue or ABPAS)

 small amounts of fibrin may be present as fibrillary eosinophilic material.
 perivascular lymphocytes (perivascular lymphocytic infiltratein superficial and mid dermis)
 +/- neutrophils and nuclear dusts
 +/- vasculitis near foci of necrobiosis

Evolutive forms

 early interstitial GA or incomplete GA lesions

• interstitial pattern
• lymphocytes around vestaining with colloidal iron or Alcian blue at pH 2.5.

 fully evolved GA lesions and deep subcutaneous GA nodules

• palisaded granulomatous dermatitis
• septal and lobular panniculitis
• macrophages surround acellular necrobiotic areas in which collagen bundles are thinned, or they sometimes have a pale, homogeneous, light-blue appearance, the latter of which is due to the presence of mucin.

 subcutaneous GA and dermal infiltrates

• deeply eosinophilic centers of granulomas contain degenerated, homogeneous-appearing collagen
• necrotic small vessels in the centers of palisaded foci surrounded by nuclear dust
• fibrinogen shown by direct immunofluorescence in the centers of palisaded granulomas

 perforating GA

• necrobiotic material is extruded through focal perforations
• epidermal hyperplasia at the edge of the perforation forms a pseudochannel communicating with underlying necrobiotic granuloma

 nonnecrobiotic GA, sarcoidal GA, or tuberculoid GA

 Mucin in GA is hyaluronic acid and is visible in sections stained with hematoxylin and eosin as faintly basophilic stringy material.

Variants:

 classical granuloma annulare
 interstitial granuloma annulare
 deep granuloma annulare
 perforating granuloma annulare

Differential diagnosis:

 palisading granulomas

• rheumatic nodule
• necrobiosis lipoidica
  • multilayered necrobiosis (stacks of plates) with open ends
  • numerous plasma cells
  • thickened collagen bundles within palisaded granuloma
  • diffuse process present throughout the reticular dermis

 palisaded neutrophilic and granulomatous dermatitis

 foreign body granulomatous dermatitis
 infection
 sarcoidosis
 soft tissue tumors and fusiform cell sarcomas

• epithelioid sarcoma
• plexiform fibrohistiocytic tumor

See also

 palisading granuloma