Unlike humans, in which pulmonary aspergillosis is the most common clinical presentation, dogs usually present a sinonasal or, more infrequently, a disseminated aspergillosis. Canine sinonasal aspergillosis (SNA) primarily affects young to middle-aged, mesaticephalic or dolichocephalic immunocompetent dogs. Even if it remains an uncommon condition, SNA is the second most common cause of purulent nasal discharge after neoplasia. Several diagnostic tools are available including immune-based tests and culture, nonetheless, rhinoscopy and histopathology are among the most reliable. 

A ten year old German shepherd dog presented a history of chronic coughing, recently coupled by repetitive sneezing. The animal was prescribed with NSAID for one week and doxycycline for 15 days. At the end of treatment signs of unilateral right epistaxis were observed and the animal was hospitalized. Haemorrhage was promptly stopped by topical adrenaline. No history of rodenticide use was recorded.  A complete blood work revealed no significant changes and immune based tests for Dirofilaria sp.; Leishmania sp. and Erlichia canis resulted all negative. Rhinoscopy was then performed. It revealed a congestive and hyperaemic nasopharynx with a seropurulent discharge and a purulent discharge in the right nasal cavity, coupled with signs of turbinate osteolysis, but no fungal plaques were observed. Antibiotic therapy was changed to a fluoroquinolone/beta-lactamic association with an anti-inflammatory dose of prednisolone, until laboratory results. Histopathology of mucosal biopsy performed during rhinoscopy revealed a pyogranulomatous inflammation with no neoplastic cells. Microbiology revealed a coagulase positive Staphylococcus sp. 
Although sneezing significantly diminished with treatment, nasal discharge became more abundant and was associated with a progressive nasal planum depigmentation, which led to the suspicion of SNA.  A computerized tomography scan (CT) was performed. As CT showed extensive turbinate osteolysis, but an intact cribiform plate, sinusotomy was carried out. It included sinusal washing with sterile 0.9% saline solution and the application of a 1% clotrimazole ointment. During surgery, aseptic collection of sinusal content was performed for a second microbiology culture, which later resulted in Aspergillus spp. isolation. During the 10 days after surgery, epistaxis progressively diminished until complete remission. In the following weeks complete recover was considered, as nasal planum depigmentation reverted and a slight right nasal serosal discharge was occasionally recorded.
Discussion: 
ASN diagnosis remains challenging even for the skilled veterinary surgeon, as clinical presentation denotes a set of unspecific upper airway signs.  In the presence of immunocompetent dogs, with no history of trauma, ASN is rarely considered a differential diagnosis, particularly if not supported by the observation of fungal plaques by rhinoscopy and absence of histopathological and microbiological confirmation. Also, epistaxis is far more frequently the sign of other vector borne infectious or parasitic diseases, or neoplasia. In this case, Aspergillus sp. culture was only positive when samples were collected during sinusotomy and empirical treatment, approximately a long 4 months after the first consult. This case has proven that a wise clinical judgement and a comprehensive differential diagnosis in the absence of laboratory confirmation is still critical for ASN successful management.

Canine Nasal Aspergillosis: review of diagnostic challenges about a case report