August 2016



Signalment (JPC 21474-5/6):  2-year-old dog 

HISTORY:  This dog from Florida had an expanding 3 cm circular indurated granuloma with numerous sinuses and fistulas in the skin over the right flank. 

HISTOPATHOLOGIC DESCRIPTION:  SLIDE A:  Haired skin:  Affecting up to 75% of the deep dermis and subcutis, extending into the panniculus and separating and surrounding skeletal myofibers are coalescing 0.5-2mm inflammatory nodules centered on faint negative images of fungal hyphae embedded in eosinophilic cellular and karyorrhectic debris (lytic necrosis).  Necrotic foci and fungal hyphae are surrounded by numerous epithelioid macrophages, lymphocytes, plasma cells, and few neutrophils, with occasional multinucleated giant cells (foreign body and Langhans' type), admixed with fibroblasts and scant fibrous connective tissue. Inflammation extends into the adjacent adipose tissue and skeletal muscle.  Remaining skeletal myocytes are often shrunken with fragmented hypereosinophilic sarcoplasm and nuclear pyknosis (necrosis), or pale, swollen and vacuolated (degeneration).  Multifocally, scattered macrophages contain brown, intracytoplasmic pigment (hemosiderin).  Diffusely, there is mild orthokeratotic hyperkeratosis. 

Slide B:  Gomori methenamine silver (GMS):  Within the pyogranulomas are many, argyrophilic hyphae and hyphal fragments.  Hyphae are occasionally septate, 4-15um in width with non-dichotomous branching and thin, non-parallel walls. 

MORPHOLOGIC DIAGNOSIS:  Haired skin: Dermatitis and panniculitis, nodular, granulomatous, multifocal and coalescing, marked, with numerous fungal hyphae, breed not specified, canine. 

ETIOLOGIC DIAGNOSIS:  Cutaneous zygomycosis 


  1. Order Mucorales:
    1. Systemic disease called “mucormycosis”
    2. Genera: Absidia, Mucor, Rhizopus, Rhizomucor, Mortierella
  2. Order Entomophthorales
    1. Subcutaneous disease called “entomophthoromycosis”
    2. Genera: Basidiobolus, Conidiobolus
    1. Rhinocerebral
    2. Cutaneous/subcutaneous (most frequently in horses) – Basidiobolus haptosporus (horse) & Conidiobolus coronatus (dogs) most common
    3. Systemic
      1. Pulmonary
      2. Gastrointestinal







Gross (cutaneous granulomas):




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