Successful surgical resection of a multilobular osteochondrosarcoma arising from the costal cartilage in a cat

Abstract

A 10-year-old neutered male cross-bred cat was referred to our clinic for a solid mass tightly fixed to the right side of the thoracic wall from the 2nd to 4th ribs. Computed tomography revealed the mass had remarkable calcifications and arose from the 3rd costal cartilage. After removal, it was diagnosed histopathologically as a multilobular osteochondrosarcoma (MLO). For tumor resection, extremely wide surgical margins included 6 costal cartilages and 3 sternal segments were required; however, the tumor was successfully resected, followed by reconstruction of the thoracic wall using artificial materials. The cat recovered uneventfully and was good in health for ~4 y. This is apparently the first report of surgical resection of MLO from the costal cartilage of a cat.

Key clinical message:

To our knowledge, this is the first report of MLO from the costal cartilage in a cat, demonstrating aggressive surgical resection despite extremely wide surgical margins.

Multilobular osteochondrosarcoma (MLO) in cats is an extremely rare bone-cartilage tumor; to our knowledge, only 5 cases have been reported (1–5). This tumor is also infrequently reported in dogs, usually arising from the periosteum of a flat bone, most commonly the skull. It typically is slow growing, locally invasive, unlikely to metastasize, and generally has a good prognosis (6,7). Histopathology of MLO typically includes various lobules with fibrous septa and a central core of cartilage or bone matrix (1–4). The present case report describes successful surgical resection of MLO arising from a costal cartilage in a cat.

CASE DESCRIPTION

A 10-year-old neutered male cross-bred cat was referred to our clinic because of a solid mass (L: 63 × W: 46 × H: 40 mm), tightly fixed to the right side of the thoracic wall from the 2nd to 4th ribs. The cat had a body temperature of 39.0°C, pulse of 180 beats/min, and respiratory rate of 30 breaths/min. A complete blood (cell) count and clinical chemistry analysis detected no abnormal findings, and the cat was negative for both FeLV antigen and FIV antibody.

Computed tomography (CT) revealed a well-defined, round, soft tissue-density mass with an irregularly marginated osseous tissue. The mass slightly compressed the thoracic wall and had mild contrast enhancement on its rim (Figure 1 A). On a dorsally reconstructed contrast image, the sternum was displaced slightly to the left (Figure 1 B). A bone window transverse plane image revealed the mass arose from the 3rd costal cartilage (Figure 1 C), whereas a 3-dimensional left lateral thorax reconstructive bone image showed a remarkably calcified mass tightly adherent to the 3rd costal cartilage (Figure 1 D).

FIGURE 1.

Computed tomograpic imaging of a multilobular osteochondrosarcoma arising from the costal cartilage in a cat. A — The soft tissue window post-contrast transverse image had a well-defined, round, soft tissue-density mass with an irregularly marginated osseous tissue (asterisk). The mass slightly compressed the thoracic cavity (arrowhead) and had mild contrast enhancement on its rim (arrow). B — On the post-contrast dorsally reconstructed image, the sternum was displaced slightly to the left (arrow). C — The bone window transverse plane image revealed a nonhomogeneous radiopaque mass with neoplastic osteogenesis centered on the 3rd costal cartilage (arrow). D — The 3-dimensional left lateral reconstructive bone image showed a remarkably calcified mass adhered tightly to the 3rd costal cartilage.

Surgical resection was done 10 d after the initial examination. The cat was premedicated with fentanyl citrate (0.05 mg/kg, IV) and anesthesia was induced with propofol (4 to 6 mg/kg, IV). The cat was intubated and anesthesia maintained with sevoflurane (0.5 to 2.5%, in a mixture of 1:1 oxygen and air) using a mechanical ventilator (AWP: 7 to 10 cmH₂O, TV: 45 to 94 mL, PEEP: 1 to 2 cmH₂O). Concurrent with induction of anesthesia, additional analgesia included a continuous microdose infusion of fentanyl citrate (2 to 5 μg/kg per minute for 5 d) and ketamine hydrochloride (150 to 600 μg/kg per minute for 3 d). Ampicillin sodium (20 mg/kg, IV) was given every 2 h during the intraoperative period and q12h for 4 d after surgery. Famotidine (1 mg/kg, IV) was given q24h for 4 d. On the 1st day after surgery, a single dose of meloxicam was administered (0.1 mg/kg, SC).

The large mass located on the right ventrolateral thoracic wall was completely resected. Briefly, the mass had arisen from the surrounding soft tissue and 3rd costal cartilage (Figure 2 A). The surgical margin of the lateral region of the tumor superficially was the transverse pectoralis muscle and descending pectoralis muscle, and the deep margin was the abdominal obliques. The surgical margin of the ventrolateral area was from the 2nd to the 4th costal cartilages and included 3 sternal segments with a 2-centimeter margin beyond visible tumor. The intercostal muscles and pleura were included to ensure a deep margin (Figure 2 B). After resection of the mass, the large thoracic wall defect was closed with artificial materials (2-millimeter-thick Gore Dualmesh; Japan Gore CJV, Tokyo, Japan). The mesh covered the inside of the thoracic cavity, and mattress sutures were used to join the mesh to the edges of the pleura and intercostal muscle to close the thoracic cavity (Figure 2 C). Thereafter, the mesh was covered with the remaining deep pectoral and superficial pectoralis muscles and the latissimus dorsi (Figure 2 D). The skin was closed in a routine manner. The cat recovered uneventfully and remained healthy for ~4 y.

FIGURE 2.

Intraoperative views of a multilobular osteochondrosarcoma arising from the costal cartilage in a cat. A — The large mass (L: 63 × W: 46 × H: 40 mm) was in the frontal right side of the thoracic wall, surrounding the 3rd costal cartilage. B — Surgical resection of the mass was done with a 2-centimeter margin. Briefly, right and left costal cartilages (3 cartilages from 2nd to 4th) and the corresponding 3 sternal segments (ditto) were resected. C — The wide-range deficit of thoracic wall was covered with 2-millimeter-thick biomaterial mesh (Gore Dualmesh; Japan Gore CJV, Tokyo, Japan) placed inside the thoracic cavity. D — The mesh was additionally covered with the remaining deep and superficial pectoralis muscles and the latissimus dorsi.

The resected mass was fixed in 10% neutral-buffered formalin, routinely embedded in paraffin, sectioned at 4 μm, and stained with hematoxylin and eosin. At histopathological examination, the mass had a typical multiple-lobulated structure composed of a central core with mature chondrocytes, separated by thin, fibrous tissue (Figure 3 A). It was adjacent to the 3rd rib and costal cartilage with mild reactive bone proliferation at the boundary with those structures (Figure 3 B). The tumor was mostly composed of mature chondrocytes, whereas dense chondroblast proliferation was present at the periphery (Figure 3 C). Occasionally, osteoid formation was observed within the tumor (Figure 3 D). The mass was diagnosed as MLO.

FIGURE 3.

Histopathological micrographs of the mass in this cat. Hematoxylin and eosin stain, scale bar = 100 μm. A — The tumor showed a typical multiple-lobulated structure composed of a central core with chondrocytes (circle) and separated by thin, fibrous septa (arrows). B — The tumor (thin arrows) was adjacent to the 3rd rib and costal cartilage (arrowhead) and showed mild reactive bone proliferation at the boundary (thick arrow). C — The tumor was mostly composed of mature chondrocytes (upper left), whereas dense chondroblast proliferation was also observed peripherally (lower right). D — Osteoid formation was occasionally observed within the tumor.

DISCUSSION

Multilobular osteochondrosarcoma is an uncommon, bone-cartilage-related tumor in the cat. To our knowledge, only 5 cases have been reported, 4 of which arose from the skull (parietal and occipital region, frontal bone, cranium, and mandible, respectively) and another from a rib (1–5). Although this tumor can develop from any flat bone, most arise from the skull. In dogs, the most common site was also the skull, including the mandible, maxilla, cranium, zygomatic arch, orbit, and tympanic bulla; plus the pelvis, rib, and os penis (6–9). To our knowledge, this is the first report of MLO originating from the costal cartilage.

In the present case, the surgical margins were extremely wide and included 6 costal cartilages and 3 sternal segments. The tumor was successfully resected and the thoracic wall reconstructed.

It is well-known that CT images, especially bone window images, provide important information in dogs with MLO. Those characteristic images were reported to show a well-defined, round-to-oval shape, nonhomogeneous bone opacity, coarsely granular appearance, stippled calcification, bone formation, soft-tissue calcification, and bone lysis (8–10). Similar CT images were reported in cats to show coarse mineralization (arising from the skull) (4), a well-defined, round shape with nonhomogeneous opacity and coarsely stippled mineralization (arising from the rib) (3), and heavy calcification (arising from the mandible) (5). Computed tomographic imaging is expected to be a useful tool for planning and conducting surgery for MLO in cats, as in dogs.

It is widely accepted that surgical resection is the preferred treatment for MLO, as neither chemotherapy nor radiation is effective (6,8,11,12). As MLO is slow-growing, unlikely to metastasize, locally invasive, and likely to recur, a wide range of surgical margin is important for preventing recurrence of MLO in dogs (11–13). In 12 dogs treated with surgical resection alone, 7 dogs (58%) had local recurrence, with a median time of 14 mo. However, when complete resection with sufficient surgical margin was done, no local recurrence was observed (6). Multilobular osteochondrosarcoma was graded histologically using 6 morphological criteria, including invasion of borders, size of lobules, organization, mitosis, pleomorphism of cells, and necrosis (14). In addition, postoperative survival time was closely related to the grade, with > 29.9 mo of survival time, > 44.4 mo to local recurrence, and > 27.3 mo to metastasis after surgical resection in Grade-I MLO, the least serious level of grading (7). A case of severe, inoperable feline MLO arising from the rib was graded as Grade-II MLO (3). In a dog, malignant MLO arising from the skull (2) had local recurrence at 2 mo postoperatively. In addition, a postoperative duration of ~18 mo was obtained by surgical resection with a wide surgical margin in cats (5). In the present case, an extremely wide surgical margin included 6 costal cartilages and 3 sternal segments, and the cat had no recurrence within ~4 y. Although reported cases of feline MLO are limited, complete resection with sufficient surgical margin should prolong survival.

In conclusion, this is apparently the first report of MLO arising from costal cartilage in a cat. The MLO was successfully removed by aggressive surgical resection and extremely wide surgical margins.