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case_images: Left hindlimb skeletal muscle metastasis of an urothelial carcinoma before being surgically removed. The mass produced a deformity in the lateral head of the gastrocnemius muscle (circle)
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case_images: On palpation, several masses affecting the long muscles of the left forelimb and both hindlimbs were detected (Figure 1).
case_images: (a) Hip extended ventrodorsal radiographic projection including craneocaudal radiographic view of both stifles and (b) mediolateral projection of the left hip and stifle, at the time of presentation. There is a periosteal reaction, with less opacity than the bone, on the cranial and medial aspects of the femur (white arrows), as well as sclerosis in the corresponding area of the diaphysis (asterisks). The inner cortex or endosteum is intact. (a) There is also remodelling of the right proximal fibula (arrowheads), where a nodule was further detected by ultrasonography in the fibularis (peroneus) longus muscle. (b) In addition, increased radiopacity of soft tissue at the caudal aspect of the left stifle is present (arrowheads)
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case_images: Radiographic examination of the affected limbs and thorax under sedation revealed an active periosteal reaction involving the cranial and medial proximal third of the left femoral diaphysis, changes in the shape of the right proximal fibula and increased radiopacity of the caudal thigh and caudal crural muscles related to the stifle (Figure 2).
case_images: (a) Right kidney with normal size range, hyperechogenic cortex and irregular margins. A hyperechoic wedge-shaped section, consistent with chronic renal infarction, is seen in the renal cortex (asterisk). (b) The left kidney is slightly smaller than normal, also evidencing irregular margins, hyperechogenic cortex and an area of chronic renal infarction (asterisk); moreover, the caudal pole is structurally disorganised and a medullary band sign can be observed (arrows). (c) The ultrasonographic features of the urinary bladder are within normal limits
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case_images: No other significant changes were seen on ultrasonography of the lower urinary tract and abdomen (Figure 3).
case_images: (a) Ultrasound images of the cystic mass located within the left semimembranous muscle. There is an anechoic central area with a band of hypoechoic organised tissue. (b) Colour Doppler visualisation of the lateral head of the left gastrocnemius muscle. Vascularisation of the mass is scarce (score 1) preferentially peripheral and occasionally central. (c) Longitudinal axis of the mass located in the superficial digital flexor muscle of the left hindlimb, as the lesions progressed the band of higher echogenicity was wider and more heterogeneous and the central anechoic area smaller sometimes with a trabeculated structure. (d) Superficial digital flexor muscle, the surrounding reactive tissue showed more hyperechogenic foci, with variable acoustic shadows, consistent with a higher degree of intralesional fibrosis. (e) Vastus medialis, there is periosteal reaction of the adjacent left femur proximal diaphysis. (f) Superficial digital flexor muscle, more advanced lesions showed anechoic foci located both in the central area and the surrounding connective band. The smallest nodule, located in the lateral head of the left gastrocnemius muscle, measured at the first visit 1.84 x 1.03 cm, whereas the largest recorded mass, measured 2 weeks later, affected the left superficial digital flexor muscle and had grown from 3.95 x 2.13 cm to a size of 5.36 x 2.63 cm
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case_images: A first ultrasound examination of the limbs (linear probe 10-12 MHz; Esaote Mylab 30 Gold VET; Probovet) revealed round to oval lesions characterised by an anechoic centre that contained more or less evident echogenic bands resembling a trabeculated structure, surrounded by a thick hyperechoic peripheral band (Figure 4a). The colour Doppler study of some of the lesions showed that they were poorly vascularised (grade 1) (Figure 4b). The size of the lesions was increased and the larger showed several anechoic centres with a peripheral band displaying hyperechoic areas with acoustic shadows (Figure 4c-f).
case_images: (a) Fine-needle aspiration cytology showing a large cluster of tumour cells. (b) Large, isolate and pleomorphic neoplastic cells between abundant cell debris, with occasional intracytoplasmic vacuoles (signet ring cells) (arrows) (Giemsa)
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case_images: An ultrasound-guided, fine-needle aspiration of a nodule from the lateral head of the right gastrocnemius muscle was performed and yielded a highly cellular sample with abundant large, pleomorphic tumour cells, isolated or forming cluster aggregates, admixed with cell debris (Figure 5a). Pale intracytoplasmic inclusions or vacuoles consistent with signet ring cells (Melamed-Wolinska bodies) were occasionally observed (Figure 5b).
case_images: Gross and microscopic features of an intramuscular metastasis of a urothelial carcinoma. (a) Sagittal section of a well delimitated cystic-nodule showing a thick and whitish wall with a narrow lumen. (b) Microscopically, at low magnification, there are numerous infiltrating cords, nests and papillary structures of neoplastic urothelium (black arrows) conforming the tumour wall, which delineated a central lumen (see asterisks in [b] and [c]). Muscle fibres appear displaced at the outer part of the lesion (arrowhead). (c) Detail of the urothelium showing umbrella cells at the surface (black arrows), intracytoplasmic vacuoles (Melamed-Wolinska bodies) in intermediate layer and cystic degeneration of neoplastic cells (arrowhead)
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case_images: On the surgical section, the nodule showed a thick, firm and whitish wall delineating a narrow central cavity filled with necrotic cells debris (Figure 6a). Microscopically, the wall of the cystic nodule was formed by tubule-papillary structures covered by a neoplastic transitional epithelium (urothelium) supported by moderate to abundant fibrous stroma (Figure 6b,c). Melamed-Wolinska bodies. Moreover, pseudocysts due to intraepithelial degeneration of neoplastic cells were often observed (Figure 6c).
case_images: Intramuscular metastatic urothelial carcinoma. (a) AE1/AE3 antibody shows diffuse and strong labelling of all layers of the neoplastic urothelium. (b) Immunolabelling for vimentin is limited to the stroma of the nodule. The neoplastic urothelial cells are negative. (c) Uroplakin III expression is absent or weakly positive throughout the neoplastic urothelium, while many superficial neoplastic cells strongly react with the antibody. (d) Cytokeratin 7 expression is observed by numerous superficial umbrella cells and randomly reacted with isolated cells of the intermedia layers. (e) Cytokeratin 20 is moderately expressed throughout all cell layers. (f) Ki67 is strongly expressed by the nuclei of most tumour cells
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case_images: The neoplastic epithelial cells showed an intense and diffuse cytoplasmic immunolabelling for AE1/AE3 throughout all strata (Figure 7a). Vimentin antibody strongly reacted with the stroma of the tumour and rarely with neoplastic cells (Figure 7b). UPIII expression was weak-moderate-intense and randomly distributed throughout the neoplastic urothelium; individual superficial neoplastic cells, umbrella cells, strongly express UPIII (Figure 7c). CK7 antibody strongly reacted with many superficial cells but also was irregularly expressed by neoplastic cells of the intermedia and basal layers (Figure 7d). CK20 antibody showed weak and irregular immunolabelling of all layers of the neoplastic urothelium (Figure 7e). Ki67 antibody was strongly expressed in numerous nuclei of the tumour cells (Figure 7f).