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EQUINE VETERINARY EDUCATION / AE / MARCH 2015


Nuclear scintigraphy of the proximal femur was helpful, but


a definitive diagnosis could not be determined. Nuclear scintigraphy revealed severe IRU in the proximal femur and differential diagnoses included fracture, avulsion of the insertion of the tensor fascia lata or superficial gluteal muscle, or neoplasia. Radiographs of this area did not reveal any visible abnormalities. The lack of radiographic findings was not surprising due to the large amount of superimposition encountered in this region despite multiple radiographic projections. The use of ultrasound was more sensitive to evaluate the region for ligamentous avulsion or irregularities within the surrounding muscles or periosteal margin, but could also not definitively provide a cause for this horse’s lameness. As the horse was not clinically affected in the forelimbs or


Fig 5: Schmorl’s node with underlying metastatic neoplastic cells and osteolysis. Fibrocartilaginous disc material (*) is focally herniated through the vertebral endplate of the cranial aspect of the 5th cervical vertebra. The trabecular osseous framework is replaced by neoplastic cells accompanied by fibroplasia (arrow) in the areas underlying the herniated disc material. Haematoxylin and eosin, bar = 2 mm.


SCC metastasis supports the rarity of this neoplasia metastasising to bone. Although rare, horses with penile SCC should be evaluated for signs of metastasis especially in those cases with chronic or undiagnosed lameness or secondary clinical signs such as dyspnoea. The apparent lack of lymph node enlargement is


interesting in that this is the most common site of metastasis in horses (van den Top et al. 2011) and human patients with penile SCC (Pow-Sang et al. 2010). In this case, where 2 rare sites of distant metastasis were present, enlarged superficial inguinal, deep inguinal or medial iliac lymph nodes would be expected. Although none of these lymph nodes was palpably enlarged, metastasis could be ruled out based upon palpation alone (van den Top et al. 2011). Lymph nodes were not evaluated histologically due to


their grossly normal appearance and this was an oversight of the investigation. In a large case study of 114 horses with penile or preputial tumours, 28 had regional lymph node enlargement with only 9 (32%, 8 SCC) demonstrating metastasis (van den Top et al. 2011). Enlarged lymph nodes without metastasis had evidence of regional inflammation and lymphoid hyperplasia rather than metastatic neoplasia. Conversely, in 54 horses with apparently normal inguinal lymph nodes, 5 (9.3%, all SCC) had histological evidence of metastasis (van den Top et al. 2011). Similarly, in man, up to 58% of patients with penile SCC have enlarged palpable inguinal lymph nodes. Less than 50% of these enlarged lymph nodes have histological confirmation of neoplasia. Additionally, about 20% of cases without palpably enlarged lymph nodes have histological confirmation of metastatic disease in the lymph node (Ornellas et al. 1994). In man, distant metastasis without regional lymph node metastasis is unusual (Barocas and Chang 2010; Pow-Sang et al. 2010), but has been reported (Chaux et al. 2011). Therefore, enlarged inguinal lymph node aspirates should be considered in cases of SCC, but the decision to aspirate should not be made merely on lymph node size.


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neck on initial evaluation, these areas were not assessed by the nuclear scintigraphy scan. However, the cervical region would have been likely to demonstrate similar IRU as the right hindlimb. This may have led to further diagnostic examinations of the neck including radiography and ultrasound. Since the neck pain did not present until the owner decided on euthanasia, this finding was appreciated only on post mortem examination. The authors advocate that practitioners consider whole body nuclear scintigraphy scans in cases of suspected skeletal metastasis. However, in this case, the proximal femur was not suspected to be a source of lameness until after the completion of the scintigraphy scan when the images were analysed. If there is severe IRU noticed during the scan, further regions could be imaged before the isotope is completely excreted. Further diagnostic tests to evaluate the area of IRU could


have included a bone biopsy. Since a fracture could not be ruled out, biopsy of the femur was considered, but not performed due to potential propagation of a fracture. The authors are unaware of any specific reports describing pathological fracture following bone biopsy in horses, but this complication has been described in man (Gladden and Spill 2011). However, with both presumed diagnoses potentially compromising bone integrity of the femur, the authors were concerned that fracture propagation was possible following the bone biopsy. Considering the risks for determining a definitive diagnosis at that time, the owner elected conservative management. A definitive cause of the ventral abdominal and preputial


oedema was not determined from clinicopathological or post mortem examinations. It is possible that the SCC neoplasm in the femur led to local venous congestion and oedema formation. With gravity dependence, this oedema would have localised to the ventral abdomen and prepuce. This hypothesis could be supported if the oedema began caudally near the right hindlimb; however, the owner noticed both locations of oedema simultaneously and both sites were symmetrically affected at that time. Moreover, if local recurrence of SCC was observed on the penis or preputial sheath, this pattern of oedema could be explained, but the authors did not observe local recurrence of the neoplasm. This report demonstrates the history, presentation,


diagnostic methods and clinical outcome in a horse with multiple skeletal metastases following SCC of the penis. In man, radiographs or computed tomography of the thorax and/or abdomen are typically performed to screen for distant metastasis prior to tumour staging (Barocas and Chang 2010) and may be considered in equine patients. Lymph node aspiration and metastatic imaging have been included in a


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