Signalment:  

6-week-old male Swiss Webster mice (Mus musculus).Multiple animals were euthanized due to visible swellings and masses around the head and mouth. Development of a head tilt was noted in some.

Gross Description:  

All mice were in good body condition at postmortem examination. Multiple, small white nodules (ranging from 2-10mm diameter) were present subcutaneously around the head, especially in the parotid and submandibular areas. On coronal sectioning of the head after fixation and decalcification, similar nodules effaced and expanded many tissues multifocally from the rostral to caudal aspect of the head. Nodules were firm and contained tan-brown fluid on cut section. 

Histopathologic Description:

Multiple coronal sections of the head are submitted. Lesions and anatomic structures captured subsequently vary on different sections. Multifocal to coalescing, large, discrete inflammatory cell aggregates bilaterally, efface and expand the ventrolateral aspects of the head, predominantly the mandibular bone, molar teeth, skeletal (masseter) muscle, adipose tissue and skin. Aggregates are composed of central foci of 2-3μm diameter cocci admixed with hyalinized, amorphous material that frequently forms peripheral, radiating, club-like projections (Splendore-Hoeppli material). Within and encircling these cores there are many neutrophils admixed with necrotic cell debris and basophilic mineralized foci. These foci are in turn encircled by epithelioid macrophages, lymphocytes, fibroblasts and collagen fibers. Additional associated microscopic changes include: thickening of mandibular bone by subperiosteal woven bone formation, bone lysis and increased numbers of osteoclasts, odontoclastic resorption of molar teeth, and skeletal myocyte loss/atrophy. Epidermal parakerototic hyperkeratosis and sub-epidermal pustule formation are additionally seen. 

Morphologic Diagnosis:  

Multifocal to coalescing, necrosuppurative osteomyelitis, myositis, panniculitis, dermatitis and cellulitis, with Splendore-Hoeppli material and intralesional bacterial cocci, bone lysis and subperiosteal woven bone formation.

Lab Results:  

Staphylococcus aureus was cultured from the lesions.

Condition:  

Botryomycosis

Contributor Comment:  

Splendore-Hoeppli material is the bright eosinophilic, club-shaped material that typically radiates around bacterial colonies in histologic sections.(1,4,5) Classically this phenomenon has been described in cases of chronic staphylococcal infection which is associated with formation of grossly visible bacterial colonies that resemble granules. The term botryomycosis is used to refer to such chronic infections where Splendore-Hoeppli material is seen. This condition usually affects the skin and subcutis and is typically initiated by a skin wound, resulting in lesions that present as local, firm nodules, ulcers or sinuses communicating with deep abscesses.(4,5) Ultimately these lesions may be walled off by fibrous connective tissue and can coalesce to form aggregates of granulomas within the subcutis and surrounding tissues.(4,5) Botryomycosis may also involve other organs such as the lung, and although it can affect immunocompetent animals, immunosuppression is considered to be a predisposing factor to its development.(1,2,4,5,8)

In addition to staphylococci (S. aureus, S. hominus, S. xylosus), other bacterial agents have also been isolated from cases of botryomycosis in rodents, including, Streptococcus intermedius, Pseudomonas aeruginosa, Proteus spp., Escherichia coli and Nocardia asteroides.(1,3,4,8,11) In other animals and in people however, Splendore-Hoeppli material has been reported to arise in association with infections due to fungi and other parasites, and has also been known to surround biologically inert substances such as suture material.(1,3,4,5,7,12)

Although the exact nature of this reaction is unknown, it is considered to be a localized immunological response to an antigen-antibody precipitate related to fungi, parasites, bacteria or inert materials.(5) The characteristic formation of the Splendore-Hoeppli reaction around infectious agents or biologically inert materials probably represents some attempt at containment of the agent on the part of the host. It likely prevents phagocytosis and intracellular killing of the injurious agent leading to chronicity of infection, so whether this degree of immune responsiveness is actually helpful or harmful remains to be determined.(5,6)

Similarly the nature of the intense eosinophilic nature of this material remains poorly understood, but is thought to be due to its composition of antigen-antibody complexes (immunoglobulins and major basic proteins) combined with cell debris from inflammatory cells (lymphocytes, plasma cells, eosinophils and macrophages) and fibrin.(5) Composition of the reaction likely depends on the type of causative agent, and one hypothesis is that Splendore-Hoeppli material may be derived from host leukocytes that aggregate in response to the bacteria, parasites or inert foreign materials that can initiate the reaction.(5,6)

Morphological mimickers of the Splendore-Hoeppli reaction are said to include flame figures (as seen in conditions such as feline eosinophilic granuloma complex, insect bites and drug eruption), tophaceous lesions of gout, asteroid bodies (as may be rarely seen in some granulomatous lesions in animals) and actinomycotic sulfur granules (the radiating structures of Splendore-Hoeppli reaction resemble these sulfur granules). The absence of central branching filaments in Splendore-Hoeppli reaction helps to distinguish this from true actinomycotic sulfur granules.(5)

Flame figures represent degranulated eosinophils that form aggregates of granular necrotic material surrounded by collagen, and these foci are often basophilic with peripheral macrophages.(5) Gout tophi appear as variably sized deposits of amorphous, amphophilic material with parallel, acicular clefts; however, these crystals often have a brownish color and are doubly refractile with polarized light.(5) Asteroid bodies are stellate eosinophilic inclusions seen within giant cells of granulomas occasionally.(5) This reaction is histologically opposite to that which is seen in the Splendore-Hoeppli reaction, i.e., a central stellate acellular region that is surrounded by inflammatory cells.(5)

JPC Diagnosis:  

Skin, subcutis and maxilla: Cellulitis, dermatitis, myositis and osteomyelitis, pyogranulomatous, multifocal to coalescing, severe, with large colonies of cocci and Splendore-Hoeppli material. 

Conference Comment:  

There was considerable slide variation in this case, with the bone involvement totally absent in some slides. Also, bone marrow was visible in some slides, and it was noted that within the marrow there was myeloid hyperplasia, with the majority of cells being granulocytes. Conference participants discussed the various causes of botryomycosis as listed by the contributor, with the addition of a recent case of subcutaneous botryomycosis in a Texas Longhorn steer caused by Bibersteinia trehalosi.(10) Participants also noted that in addition to immunosuppressed mice, urokinase-type plasminogen activator-deficient mice are particularly susceptible to developing botryomycosis.(9) This is presumed to be due to their lack of urokinase-type plasminogen activator (uPA). Plasminogen activators are serine proteinases that cleave plasminogen to form plasmin in the fibrinolytic system. Plasmin is a serine proteinase that is involved in several physiological as well as pathological processes.(1) In this case, it is its impaired role in the proteolysis of fibrin and extracellular matrix (ECM) that contributes to the increased susceptibility of uPA deficient mice to developing botryomycosis.

References:

1. Thompson ME. Proceedings: Department of Veterinary Pathology Wednesday Slide Conference 2006-2007, Conference 13, Case 1, AFIP #2812387. 
2. Bridgeford EC, Fox JG, Nambiar PR, et al. Agammaglobulinemia and Staphylococcus aureus Botryomycosis in a Cohort of Related Sentinel Swiss Webster Mice. J Clin Microbiol. 2009;46(5):1881-1884.
3. EL van den Berk G, Noorduyn LA, van Ketel RJ, et al. A fatal pseudo-tumour: disseminated basidiobolomycosis. BMC Infectious Diseases. 2006;6:140.
4. Ginn PE, Mansell JEKL, Rakich PM. Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy and Palmers Pathology of Domestic Animals. 5th ed. Philadelphia, PA: Elsevier; 2007:691.
5. Hussein MR. Mucocutaneous Splendore-Hoeppli phenomenon. J Cutan Pathol. 2008;35(11):979-988.
6. Mondino A, Blasi F. uPA and uPAR in fibrinolysis, immunity and pathology. Trends Immunol. 2004;25(8):450-455.
7. Rodig SJ, Dorfman DM. Splendore-Hoeppli phenomenon. Arch Pathol Lab Med. 2001;125:1515-1516.
8. Schlossberg D, Pandey M, Reddy R. The Splendore-Hoeppli phenomenon in hepatic botryomycosis. J Clin Pathol. 1998;51:399-400.
9. Shapiro RL, et al. Urokinase-type plasminogen activator-deficient mice are predisposed to staphylococcal botryomycosis, pleuritis, and effacement of lymphoid follicles. Am J Path. 1997;2(1):359-369. 
10. Spagnoli S, Reilly TJ, Calcutt MJ, et al. Subcutaneous botryomycosis due to Bibersteinia trehalosi in a Texas longhorn steer. Vet Pathol. 2012;49(5):775-778.
11. Weighardt H, Kaiser-Moore S, Vabulas RM, et al. Cutting edge: Myeloid differentiation factor 88 deficiency improves resistance against sepsis caused by polymicrobial infection. J Immnunol. 2002;169:28232827.
12. Zavasky D, Samowitz W, Loftus T, et al. Gastrointestinal zygomycotic infection caused by basidiobolus ranarum: Case report and review. Clin Infec Dis. 1999;28(6):1244-8.

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1-1. Head at level of olfactory bulbs

1-2. Head

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