August 2019

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 75% of the deep dermis and subcutis and extending into and separating and surrounding skeletal myofibers of the panniculus carnosus are multiple, coalescing, 0.5-2mm diameter inflammatory nodules centered on eosinophilic cellular and karyorrhectic debris (lytic necrosis) in which are embedded faint negative images of fungal hyphae and variably visible eosinophilic hyphae tubular cell walls.  Necrotic foci and fungal hyphae are surrounded by numerous epithelioid macrophages, lymphocytes, plasma cells, few neutrophils, and 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 sarcoplasm (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 4‑15um in width and are occasionally septate; have thin, non-parallel walls; and display non‑dichotomous branching.

MORPHOLOGIC DIAGNOSIS:  Haired skin: Dermatitis and panniculitis, nodular, granulomatous, multifocal to 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):

Histopathologic (subcutaneous mycoses, algae, and other infective agents)



  1. Caswell JL, Williams KJ. Infectious diseases of the respiratory system. ln: Maxie MG,ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders. 2016:573.
  2. Cullen JM, Stalker MJ. Infectious diseases of the liver. ln: Maxie MG,ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders. 2016:324.
  3. Curtis B, Hollinger C, Lim A, Kiupel M. Embolic mycotic encephalitis in a cow following Mortierella wolfii infection of a surgery site. J Vet Diagn Invest. 2017;29(5):725-728.
  4. Evans DE, Kawabata A, Wilson LD, Kim K, Dehghanpir SD, Gaunt SD, Welborn M, Grasperge B, Gill MS. Entomophthoromycosis and mucormycosis as causes of pneumonia in Vietnamese potbellied pigs. J Vet Diagn Invest. 2018;30(1):161-164.
  5. Foil C, Grooters A. Miscellaneous fungal infections. In: Green CE. Infectious Diseases of the Dog and Cat. 4th ed. Philadelphia, PA: WB Saunders Company; 2012:683-684.
  6. Ginn PE, Mansell JEKL, Rakich PM. Integumentary system. ln: Maxie MG,ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier Saunders. 2016:659-660.
  7. Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Infectious nodular and diffuse granulomatous and pyogranulomatous diseases of the dermis. In: Skin Diseases of the Dog and Cat Clinical and Histopathologic Diagnosis. 2nd ed. Ames, IA: Blackwell Science Ltd., 2005:303-309.
  1. Hargis AM and Myers S. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th St. Louis, MO: Elsevier, Inc. 2017:1083-1084.
  2. Isidoro-Ayza M, Pérez L, Cabañes FJ, Castellà G, Andrés M, Vidal E, Domingo M. Central nervous system mucormycosis caused by Cunninghamella bertholletiae in a bottlenose dolphin (Tursiops truncatus). J Wildl Dis. 2014;50(3):634-8.
  3. Madson DM, Loynachan AT, Kariyawasam S, Opriessnig T. Systemic Conidiobolus incongruus infection and hypertrophic osteopathy in a white-tailed deer (Odocoileu virginianus). J Vet Diagn Invest. 2009;21:167-170.
  1. More SN, Hernandez O, Castleman WL. Mycotic rhinitis and sinusitis in Florida horses. Veterinary Pathology. 2019;56(4):586-598.
  2. Naota M, Shimada A, Morita T, Kimura K, Ochiai K, Sano A. Granulomatous pericarditis associated with systemic mucormycosis in a finless porpoise (Neophocaena phocaenoides). J Comp Pathol. 2009;140:64-66.
  1. Ortega J, Uzal FA, Walker R, Kinde H, DIab SS Shahriar F Pamma R, Eigenheer A, Read DH. Zygomycotic lymphadenitis in slaughtered feedlot cattle. Vet Pathol. 2010;47:108-115.
  2. Quesada O, Rodriguez F, Herraez P, Seara D, Espinosa de los Monteros A. Mucor ramosissimus associated with feather loss in canaries (Serinus canarius). Avian Dis. 2007;51:643-645.
  3. Schmitz A, Korbel R, Rinder M. Zygomycosis due to Mucor racemosus associated with a circovirus infection in a Blue Tit (Cyanistes caeruleus). J Comp Pathol. 2018;165:67-71.
  4. Scott DW, Miller WH, Griffin CE. Muller & Kirk’s Small Animal Dermatology. 7th ed. Philadelphia, PA: WB Saunders Company; 2013:256-257.
  5. Sosa M, Gamble KC, Delaski K, Righton A. Clinical challenge: systemic Rhizopus microsporus infection with renal cavitation in a grey seal (Halichoerus grypus). J Zoo Wildl Med. 2013;44(4):1134-8.
  6. Ubiali DG, Cruz RA, De Paula DA, Silva MC, Mendonça FS, Dutra V, Nakazato L, Colodel EM, Pescador CA. Pathology of nasal infection caused by Conidiobolus lamprauges and Pythium insidiosum in sheep. J Comp Pathol. 2013;149(2-3):137-45.
  7. Uzal FA, Plattner BL, Hostetter JM. Forestomachs. ln: Maxie MG,ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier Saunders. 2016:42. 

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