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additional clinical signs in this horse. The authors describe their diagnostic approach and the histological evaluation of this tumour.


Balanitis or balanoposthitis Infection or inflammation of the penis and prepuce can occur as a primary finding, due to equine herpesvirus 3, Trypanosoma equiperdum, Habronema spp., Halicephalobus gingivalis (Muller et al. 2008), Pythium spp. and numerous bacterial species. As mentioned by De Meyer et al. (2017), consideration of geographical prevalence of certain infectious causes of penile and preputial inflammatory lesions is an important component of clinical evaluation. Balanitis or balanoposthitis can also accompany tumours of the penis or prepuce due to ulceration or necrosis of tissues secondary to the neoplastic process. It is important to differentiate the two aetiologies during thorough examination of the external genitalia. Histopathological assessment of tissue sections can be a useful aid in diagnostic assessment, particularly when an underlying neoplasm with secondary inflammation is suspected.


Conclusion


Diseases of the equine penis and prepuce encompass a wide variety of neoplastic and non-neoplastic lesions, the full scope of which is beyond the remit of this article. In all cases, a thorough and methodical approach to clinical evaluation is required. Whilst diagnosis of some lesions may be clinically straightforward, others may present an excellent opportunity for close dialogue between the clinician and the diagnostic pathology laboratory. Advances in molecular pathology have led to a much better understanding of the pathogenesis of many equine penile and preputial lesions, such as virally associated squamous papillomas, squamous cell carcinomas and sarcoids. Equally, in the field of diagnostic pathology, additional diagnostic modalities such as immunohistochemistry may aid in the diagnosis of specific lesions such as poorly pigmented or amelanotic melanocytic neoplasms and in such cases application of equine specific clinical research is particularly valuable.


Authors’ declaration of interests The authors have no conflicts of interest to declare.


Ethical animal research


Clients had signed standard Cambridge Equine Hospital consent forms regarding use of images for research purposes.


Source of funding The authors received no funding in relation to this work.


Acknowledgements The authors wish to gratefully thank K. Smith, Department of Veterinary Medicine, University of Cambridge, for her comments on the manuscript and for the contribution of macroscopic photographs. The authors also thank M. Fordham of the Department of Veterinary Medicine, University of Cambridge, for technical assistance in preparation of tissue sections.


Authorship


The authors contributed equally to the preparation of this manuscript.


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