Kerion dermatophytosis in a Cocker spaniel

The following are cytological and histopathological specimens taken from a discrete 1.5cm alopecic cutaneous mass on the muzzle of a 10-month-old male Cocker spaniel.

Fig 1. Fine needle aspirate. The predominant cell population consists of neutrophils and macrophages reflecting mixed-active inflammation.
Fig 2. Fine needle aspirate. Interspersed with the inflammatory cells are low numbers of fungal hyphae (red arrows) and fungal spores (black arrows).
Fig 3. H&E section. Histopathology reveals the presence of furunculosis in which free hair shafts (blue arrow) in the dermis are surrounded by a heavy inflammatory infiltrate composed of macrophages and neutrophils.
Fig 4. H&E section. On closer inspection, fungal spores similar to those seen cytologically are associated with the hair shafts (black arrows). Note the phagocytosed fungal spores within a macrophage (red arrow).

Final Diagnosis

Pyogranulomatous furunculosis associated with intralesional fungal hyphae and spores typical of dermatophytosis (ringworm).


Kerion dermatophytosis is an uncommon variant of canine ringworm in which the lesion is nodular and typically solitary, although multiple lesions may occur. It is most commonly associated with Microsporum gypseum however it can also occur with Trichophyton mentagrophytes and Microsporum canis infection. Fungal culture is required to differentiate although this may not always be successful in such lesions. Cutaneous nodules, which are essentially focal areas of furunculosis, most commonly occur on the face and forelegs, however any site may be affected. In the case of solitary lesions, surgical excision is typically curative.