History
A 9-year-old spayed female domestic shorthair cat was referred for evaluation of a 1 × 2 × 1-cm mass over the lateral aspect of the right pelvic limb. On palpation, the mass was firm, with irregular borders and an attachment proximally on the body wall. Twenty-nine months prior to examination, the cat had received a vaccine against rabies in the distal portion of the right pelvic limb. At 4 weeks of age, the cat had negative test results for FeLV and had subsequently never been vaccinated against FeLV or retested. Results of serum biochemical analysis and a CBC were within reference ranges. Thoracic radiography revealed mild bronchial wall thickening, consistent with a normal geriatric change. Computed tomographic (CT) images of the caudal portion of the abdomen and pelvic limbs were obtained before and after IV administration of iodinated contrast mediuma (Figure 1).
Contrast-enhanced computed tomographic (CT) images of the pelvic region in a 9-year-old spayed female domestic shorthair cat evaluated because of a mass over the lateral aspect of the right pelvic limb. A—Transverse precontrast CT image at the level of the hip joints. B—Transverse postcontrast CT image at the same slice location as in panel A. C—Reformatted dorsal planar postcontrast CT image of the caudal portion of the abdomen, pelvic canal, and pelvic limbs.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Contrast-enhanced computed tomographic (CT) images of the pelvic region in a 9-year-old spayed female domestic shorthair cat evaluated because of a mass over the lateral aspect of the right pelvic limb. A—Transverse precontrast CT image at the level of the hip joints. B—Transverse postcontrast CT image at the same slice location as in panel A. C—Reformatted dorsal planar postcontrast CT image of the caudal portion of the abdomen, pelvic canal, and pelvic limbs.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Contrast-enhanced computed tomographic (CT) images of the pelvic region in a 9-year-old spayed female domestic shorthair cat evaluated because of a mass over the lateral aspect of the right pelvic limb. A—Transverse precontrast CT image at the level of the hip joints. B—Transverse postcontrast CT image at the same slice location as in panel A. C—Reformatted dorsal planar postcontrast CT image of the caudal portion of the abdomen, pelvic canal, and pelvic limbs.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
An oblong soft tissue mass is present lateral to the right hip joint. The mass extends from the proximal aspect of the quadriceps muscles and into the caudal portion of the abdominal oblique muscles (Figure 2). Irregular margination with heterogeneous contrast enhancement of the mass is evident. The mass does not involve adjacent bone or the pelvic canal. Ill-defined margins of the cranial aspect of the mass are evident, with irregular linear soft tissue opacities extending into the lateral aspect of the right side of the abdominal wall. Additionally, the right inguinal and popliteal lymph nodes appear enlarged and contrast enhanced (Figure 3).
Same transverse postcontrast CT image (A) and reformatted dorsal planar postcontrast CT image (B) as in Figure 1. Notice the mass lateral to the right quadriceps musculature (panel A, arrow; panel B, arrow 1). The mass extends to the lateral aspect of the abdominal wall cranially (arrow 2). Notice the irregular contrast enhancement and margination consistent with an invasive lesion. Cd = Coccygeal vertebra. CF = Hip joint. Re = Rectum.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Same transverse postcontrast CT image (A) and reformatted dorsal planar postcontrast CT image (B) as in Figure 1. Notice the mass lateral to the right quadriceps musculature (panel A, arrow; panel B, arrow 1). The mass extends to the lateral aspect of the abdominal wall cranially (arrow 2). Notice the irregular contrast enhancement and margination consistent with an invasive lesion. Cd = Coccygeal vertebra. CF = Hip joint. Re = Rectum.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Same transverse postcontrast CT image (A) and reformatted dorsal planar postcontrast CT image (B) as in Figure 1. Notice the mass lateral to the right quadriceps musculature (panel A, arrow; panel B, arrow 1). The mass extends to the lateral aspect of the abdominal wall cranially (arrow 2). Notice the irregular contrast enhancement and margination consistent with an invasive lesion. Cd = Coccygeal vertebra. CF = Hip joint. Re = Rectum.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Dorsal 3-D color volume-rendered CT image (A) and 3-D maximum intensity dorsal CT image (B) of the right pelvic limb and region of the same cat as in Figure 1. Notice that the proximal extent of the mass and linear soft tissue opacities extend to the body wall (panels A and B, arrow 1). A large blood vessel extends into the mass, adjacent to the superimposed portion of the descending colon. Caudal portions of the mass are indicated (panels A and B, arrow 2) along with the enlarged inguinal (panels A and B, arrow 3) and popliteal (panels A and B, arrow 4) lymph nodes.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Dorsal 3-D color volume-rendered CT image (A) and 3-D maximum intensity dorsal CT image (B) of the right pelvic limb and region of the same cat as in Figure 1. Notice that the proximal extent of the mass and linear soft tissue opacities extend to the body wall (panels A and B, arrow 1). A large blood vessel extends into the mass, adjacent to the superimposed portion of the descending colon. Caudal portions of the mass are indicated (panels A and B, arrow 2) along with the enlarged inguinal (panels A and B, arrow 3) and popliteal (panels A and B, arrow 4) lymph nodes.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Dorsal 3-D color volume-rendered CT image (A) and 3-D maximum intensity dorsal CT image (B) of the right pelvic limb and region of the same cat as in Figure 1. Notice that the proximal extent of the mass and linear soft tissue opacities extend to the body wall (panels A and B, arrow 1). A large blood vessel extends into the mass, adjacent to the superimposed portion of the descending colon. Caudal portions of the mass are indicated (panels A and B, arrow 2) along with the enlarged inguinal (panels A and B, arrow 3) and popliteal (panels A and B, arrow 4) lymph nodes.
Citation: Journal of the American Veterinary Medical Association 237, 2; 10.2460/javma.237.2.155
Comments
Differential diagnoses for a palpable mass in the pelvic limb of mature cats include neoplasia, foreign body granuloma, abscess, or sebaceous cyst. Histologic evaluation of a core biopsy specimen of the mass in this patient revealed perivascular lymphocytes at the periphery of the mass, spindle cells arranged in intersecting bundles in a collagenous matrix, nuclear pleomorphism, and anisokaryosis with a high mitotic index. These characteristics were consistent with an injection-site sarcoma (ISS). Length measurement software and electronic calipers were used to determine that the maximum contrast-enhanced CT dimensions for the mass were 2.7 × 9.4 × 1.7 cm. The owner was informed that the size and extent of involvement for the mass warranted a guarded prognosis for curative resection. Immediately following CT scanning, the right pelvic limb, regional lymph tissue, and portions of the external abdominal oblique muscle were removed. Postoperative histologic evaluation confirmed popliteal lymph node metastasis, with neoplastic cells visible in the proximal surgical margins. These findings indicated that the ISS was not completely resected. The client declined to treat the cat further postoperatively with radiation therapy.
The prognosis for complete surgical resection is greatest if an ISS is identified early and if there is no evidence of extension into adjacent vital structures. Contrast-enhanced CT is currently the recommended modality for determining the complete extent of ISS involvement prior to surgery.1 Caliper measurements of ISSs equate to approximately half the mean tumor volume measured with contrast-enhanced CT. Measurements from the cat of this report demonstrate that palpation alone can substantially underestimate tumor size and extent. In this cat, palpation estimated a 1 × 2 × 1-cm structure; however, contrast-enhanced CT measurements indicated that the mass was > 4 times as large. Contrast-enhanced CT also accurately predicted tumor invasion into the body wall and likely metastasis into the inguinal and popliteal lymph nodes. These findings were not appreciated on physical examination. Although full resection of the mass was not achieved for this cat, contrast-enhanced CT provided the surgical team with a better understanding of the full extent of the mass and the presence of likely lymph node metastasis.
Ultravist 300 IV, 2.1 g, Berlex Laboratories, Wayne, NJ.
