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J Vet Clin 2024; 41(2): 133-138

https://doi.org/10.17555/jvc.2024.41.2.133

Published online April 30, 2024

Computed Tomography and Magnetic Resonance Imaging Features of Spinal Chondrosarcoma in a Cat

Minhee Lee1 , Sang-Kwon Lee1 , Juyoung Shin2 , Seulgi Bae2 , Kija Lee1,*

1Department of Veterinary Medical Imaging, College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea
2Department of Veterinary Internal Medicine, College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea

Correspondence to:*leekj@knu.ac.kr

Received: February 26, 2024; Revised: March 29, 2024; Accepted: April 2, 2024

Copyright © The Korean Society of Veterinary Clinics.

An 8-year-old, spayed female Persian cat weighing 3.6 kg presented with a lumbosacral mass and bilateral weight bearing hindlimb lameness. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed a dumbbell-shaped heterogeneous mass extending through the internal surface of the ileum and surrounding the lumbosacral junction. CT also revealed extensive osteoproliferation and bone lysis of the sacrum, but no evidence of any pulmonary metastasis. Furthermore, MRI revealed a focal area in the spinal cord showing connection with the adjacent tumor, suggesting tumor invasion into the spinal cord. Low-grade myxoid chondrosarcoma was histopathologically diagnosed. This is the first report describing CT and MRI findings of spinal cord chondrosarcoma in veterinary medicine. This study suggests that combining CT with MRI is a more sensitive tool for evaluating spinal tumors than using CT or MRI alone.

Keywords: feline, computed tomography, magnetic resonance imaging, spinal tumor, chondrosarcoma

Chondrosarcoma is a rare spinal tumor in cats. Despite being the second most common type of primary bone tumors in dogs, only 0.3% of all feline malignant tumors were identified as chondrosarcoma in a retrospective study of 938 malignant feline tumors (16,17). In another retrospective study on 85 cats with tumors affecting the spinal cord, lymphoma and osteosarcoma were the most common tumors affecting the spinal cord, followed by glial tumors, meningioma, and fibrosarcoma, whereas chondrosarcoma accounts for only 1% of all feline spinal tumors (11). They usually originate in the bones and can affect the spinal cord either by compression or invasion, resulting in clinical signs of spinal cord dysfunction and pain.

The identification of the extent and origin of the tumor is essential for surgical or radiation therapy planning. In the diagnosis of spinal tumor, computed tomography (CT) is recommended for the evaluation of the bone structure and tumor metastasis whereas magnetic resonance imaging (MRI) is recommended for the accurate margin assessment of the tumor and diagnosis of tumor invasion into the spinal cord (3,15). However, studies on the CT and MRI features of spinal chondrosarcoma in dogs are scarce, and there are no reports on the imaging features of feline spinal chondrosarcoma. In a study conducted in dogs, the CT images of spinal chondrosarcomas revealed osteolytic and osteoproliferative lesions (15). Another study investigating spinal tumors in dogs and cats demonstrated that the spinal chondrosarcoma in dogs exhibited a mass with heterogeneous contrast enhancement on MRI (1). However, a comprehensive comparison of CT and MRI findings is lacking. We herein report a case of spinal chondrosarcoma in a cat and provide detailed insights into the CT and MRI findings.

An 8-year-old, spayed female Persian cat (3.6 kg) presented with bilateral weight bearing hindlimb lameness. The owner noticed a palpable soft tissue mass in the lumbosacral junction 1 week ago. The patient exhibited right hind limb lameness approximately 6 months ago and left hindlimb lameness 1 week before the visit. There were no specific findings other than a slightly decreased general proprioception of the bilateral hindlimb in the physical and neurological examinations. On complete blood count and serum chemistry, only the blood glucose level was slightly elevated (glucose 182 mg/dL; normal range 71-148 mg/dL).

Abdominal radiograph revealed two soft tissue masses, one at the lumbosacral junction and the other in the retroperitoneum (Fig. 1A, B). Focal osteolysis of the seventh lumbar vertebra and osteoproliferation of the sacrum were also observed. Abdominal radiographs revealed no other abnormalities. On ultrasound, the masses in the lumbosacral junction and retroperitoneum had heterogeneously hypoechoic parenchyma surrounded by a well-defined margin (Fig. 1C, D). Further evaluation of the mass was impossible because of the acoustic shadowing by the near vertebral structures; therefore, CT and MRI were performed.

Figure 1.Radiographic (A, B) and ultrasonographic (C, D) images of the spinal masses of a cat in the present case. Soft tissue masses at the lumbosacral junction and retroperitoneum are identified (arrowheads). There is a focal osteolysis of the seventh lumbar vertebra and osteoproliferation of the sacrum (arrow). On the ultrasound, a mass at the lumbosacral junction (C) and a mass in the retroperitoneum (D) are observed. The masses have well-distinct margin with the surrounding tissue and had heterogeneously hypoechoic parenchyma.

CT was performed using a 32-multislice CT scanner (Alexion; Canon Medical Systems, Japan). General anesthesia was induced using 5 mg/kg propofol (Anepol; Hana Pharm, Korea) and maintained with 1.5-2.5% isoflurane (Isoflurane®; Choongwae Co., Ltd, Korea) and 1 L/min oxygen. The scanning parameters were as follows: 120 kV, 112 mA and 2.5-mm slice thickness with rotation time of 750 ms. The cat was positioned in sternal recumbency on the CT table, and thoracic and abdominal CT images were obtained. A contrast study was conducted after the intravenous administration of 600 mgI/kg iohexol (Omnipaque 300; GE Healthcare, Norway) injected at a speed of 1.5 mL/s using an autoinjector (A-60; Nemoto Kyorindo Co., Japan). Triple-phase CT images including arterial, venous, and delayed phases were obtained for abdominal CT whereas only delayed-phase images were obtained for thoracic CT. Postcontrast CT images of the artery, venous and delayed phase were obtained at 10, 45 and 100 s after injections. All CT data were cross-sectionally reconstructed in the transverse and sagittal planes at a slice thickness of 1.0 mm.

Abdominal CT revealed a single, large dumbbell-shaped mass in the lumbosacral region and retroperitoneum (Fig. 2). Notably, the mass showed a connection through the internal surface of the ileum (Fig. 2A). The mass showed mild peripheral rim enhancement and irregular contrast enhancement of the parenchyma, and a well-distinct margin with surrounding multifidus, lumbar, and gluteal muscles was observed (Fig. 2B). Extensive osteoproliferation and cortical bone lysis of the sacrum, and severe osteolysis of the vertebral body, pedicle, and transverse process of the seventh lumbar were observed (Fig. 2C, F). There was no evidence of distant metastasis to the abdominal lymph nodes. Thoracic CT showed no discernible evidence of pulmonary metastasis or thoracic lymph node enlargement.

Figure 2.Non-contrast (A, D) and venous phase (B, E) transverse CT with soft tissue window and bone window setting (C, F) transverse images in a cat with spinal chondrosarcoma. There is a dumbbell-shaped heterogeneously contrast-enhancing mass around the lumbosacral junction, connected through the internal surface of the ileum (A, B). Osteolysis (arrow) of the pedicle and transverse process of the seventh lumbar (C), and cortical bone lysis and osteoproliferation (arrowheads) of right wing of sacrum is observed (F).

MRI was performed using the 1.5T MR system (Signa explorer, GE healthcare; Waukesha, WI) for further evaluation of tumor invasion into the spinal cord. Under general anesthesia, the patient was positioned in dorsal recumbency, and the images were obtained with spin-echo sequences with a 16-channel flexible coil. T1-weighted (T1W) (TR = 649 ms and TE 11 ms, matrix size = 360 × 240), T2-weighted (T2W) (TR = 4,280 ms and TE = 102 ms, matrix size = 360 × 240), fat-suppressed T1W (TR = 604 ms and TE = 10 ms, matrix size = 288 × 224), and STIR T2W (TR = 6,812 ms and TE = 81, matrix size = 360 × 240) images of the caudal abdominal region were obtained. MR images were scanned in the transverse and sagittal planes, and gadoterate meglumine (ClariscanTM, GE healthcare, United States) was intravenously injected at a dose of 0.3 mL/kg for contrast study.

On MRI, a dumbbell-shaped mass heterogeneously hyperintense to the muscle on T2W images and isointense on T1W images was identified (Fig. 3A, B). A T2W hyperintense and T1W hypointense focal area in the spinal cord, showing connection with the adjacent mass, was identified, strongly suggesting tumor invasion into the spinal cord (Fig. 3A, C). The left sciatic nerve was clearly observed but not the right sciatic nerve; tumor invasion of the right sciatic nerve was also considered (Fig. 3D, F). Peripheral rim enhancement of the mass and strong contrast enhancement around the osteolytic and proliferative lesions was observed, suggesting primary bone tumors such as osteosarcoma, chondrosarcoma, fibrosarcoma, and undifferentiated sarcoma (Fig. 3F).

Figure 3.T2W (A, D), T1W (B, E) and post-contrast fat-suppressed T1W (C, F) magnetic resonance images in a cat with spinal chondrosarcoma. A dumbbell-shaped mass heterogeneously hyperintense to muscle on T2W images and isointense on T1W images is identified (A, B). T2W hyperintense, T1W hypointense focal area in the spinal cord, showing connection with the adjacent mass is identified (A-C, solid arrows). While the left sciatic nerve is observed in the inner side of the ilium (open arrows), the right sciatic nerve was not clearly observed (D, E). Peripheral rim sign (F, solid arrow) and septonodular enhancement (F, asterisk) is observed. Contrast enhancement (arrowheads) around the osteolytic and proliferative lesions is observed (F).

Based on the aforementioned CT and MRI findings, the primary bone tumor with adjacent invasion into the spinal cord and right sciatic nerve was at the top of the list of differential diagnosis. Soft tissue sarcoma or malignant nerve sheath tumor originating from the right sciatic nerve were also included in the differential diagnosis. A punch biopsy of the lumbosacral mass through a dorsal approach was conducted, and multinodular proliferation of mesenchymal cells embedded in a myxomatous to chondroid matrix was revealed (Fig. 4). The histopathologic diagnosis of the mass was myxoid chondrosarcoma. The patient was administered medicine for pain management but died 9 months after the diagnosis, following severe lethargy, dysuria, and dyschezia. An autopsy was not performed due to the owner’s refusal.

Figure 4.Histopathological findings from the mass around the sacrum in a cat. A mesenchymal neoplasm comprised of a multinodular proliferation of polyhedral to slightly fusiform mesenchymal cells embedded in a myxomatous to chondroid matrix is identified, which is consistent with a consistent with a myxoid chondrosarcoma. H&E stain, scale bar = 20 µm.

Based on our review of the literature, this is the first report describing the CT and MRI features of spinal chondrosarcoma, a rare spinal tumor in cats. The combination of CT and MRI was useful in evaluating bony lesions, adjacent soft tissues, and spinal cord as well as pulmonary metastasis in a cat with spinal chondrosarcoma.

While a few studies have reported the MRI features of spinal chondrosarcoma in dogs (1,15), no studies describing the MRI features of spinal chondrosarcoma in cats were conducted. The MRI features of spinal chondrosarcomas include a mass with hyperintensity on T2W, iso- to hypointensity on T1W, and mixed osteolytic and proliferative lesions (1). Another study of vertebral chondrosarcoma conducted in six dogs reported that all of the osteolytic and proliferative lesions involved the dorsal compartments of the vertebrae, including spinous processes and lamina (15). In this study, the presence of osteolytic lesions of the L7 pedicle and transverse process as well as the signal intensity of the mass was consistent with that in previous studies. However, while a previous study reported mild to marked contrast enhancement of mass parenchyma and/or the tumor margin in spinal chondrosarcoma (15), in the present study, the mass parenchyma only exhibited mild septonodular enhancement corresponding to fibrovascular septation. Similarly, in humans, the characteristics of chondrosarcoma arising from the trunk and extremities are reported to include heterogeneous contrast enhancement of the mass parenchyma with peripheral rim signs and septonodular enhancement corresponding to fibrovascular septation (6,18). Despite the lack of general contrast enhancement in the mass parenchyma, the tumor’s similarity to human chondrosarcoma warranted its inclusion in the differential diagnosis list. In addition, in the present study, strong contrast enhancement was observed around the osteolytic and proliferative lesion of the sacrum, which differs from the observations of previous studies.

In general, CT is useful in the diagnosis of the bone lesion and pulmonary metastases in tumors, whereas MRI is a more accurate techniques for evaluating the mass itself. In our case, extensive osteoproliferation and cortical bone lysis of the sacrum, severe osteolysis of the vertebral body and pedicle and transverse process of the seventh lumbar were more accurately identified on CT images. Chondrosarcomas have a lower metastatic rate than the other primary bone tumors (5). In this case report, pulmonary metastasis of the tumor was not observed on CT. MRI is useful in assessing tumor margin, neural invasion, and spinal cord invasion owing to its ability to achieve excellent soft tissue contrast (1,15) In particular, in this case report, the abnormal findings of the sciatic nerve, which could indicate invasion into the sciatic nerve, were observed only through MRI. Furthermore, the order of the hindlimb lameness, starting from the right hindlimb and extending to the left, could be explained by the right sciatic nerve invasion identified in the MRI images.

On CT and MRI, the mass, which was thought to be two masses in the lumbosacral junction and retroperitoneum on radiograph and ultrasound, turned out to be a single, large dumbbell-shaped mass extending through the internal surface of the ileum. Dumbbell-shaped tumors of the spinal region refers to separate tumors that are connected by a portion of tumor tissue transversing the neural foramen and that inhabit two or separate regions, and are categorized into nine subtypes based on location (2,9). In our case, the mass involved extralaminal, extradural and paravertebral regions, consistent with type VI dumbbell tumor (2). Dumbbell-shaped tumors are typically relatively small (12), however, similar to our case, a giant dumbbell-shaped mass has been reported in human giant lumbar schwannoma (10). Typically, the primary differential diagnosis for dumbbell-shaped tumor is a nerve sheath tumor, such as schwannoma or neurofibroma (13). A case of a dumbbell-shaped malignant peripheral nerve sheath tumor was also reported in a dog (14). However, in the case, the dumbbell-shaped mass identified as chondrosarcoma through histopathologic examination. In addition, on MRI images, the mass had a distinct contrast enhancement around the osteolytic areas of the sacrum, indicating the high possibility of a primary bone tumor rather than soft tissue sarcoma. This case suggests that bone tumors and peripheral nerve sheath tumors should be considered in patients with a dumbbell-shaped masses.

Chondrosarcomas are histologically characterized by anaplastic cartilage cells forming a cartilaginous matrix (18). Chondroblastic osteosarcoma, a subtype of osteosarcoma, also contains an abundant chondroid matrix (8). This may result in similar features on conventional MRI, such as septonodular or peripheral rim signs, which are also detected in chondrosarcomas (18). However, osteosarcoma has a high possibility of metastasis; therefore, the treatment for chondroblastic osteosarcoma must include chemotherapy before or after the surgical excision, whereas chondrosarcoma treatment dose not require chemotherapy (18). Therefore, an accurate diagnosis between chondrosarcoma and chondroblastic osteosarcoma is essential.

In humans, there has been increasing number of studies on functional MRI in oncological imaging for the characterization of the tumor in recent years (7). In particular, diffusion-weighted imaging (DWI) is a promising tool for the characterization of lesions (4). It is also employed to evaluate treatment response after chemotherapy (7). DWI contributes to cellularity and the extracellular matrix, resulting in a low ADC value in malignant tumors and a high ADC value in chondrogenesis-related tumors (4). Therefore, higher minimum ADC values are obtained in chondrosarcoma than in chondroblastic osteosarcoma due to the osteoid matrix of osteosarcoma (4). Although DWI was not performed in the present study, based on previous studies (4,18) DWI may be useful for differentiation between chondrosarcoma and chondroblastic osteosarcoma in veterinary medicine.

In conclusion, spinal chondrosarcoma is a rare tumor in cats, and CT and MRI were instrumental in diagnosing the tumor in this case. The CT images were useful in excluding pulmonary metastases and identifying osteolysis and osteoproliferation but were limited in diagnosing spinal cord and neural structures. The MRI images provided precise tumor margins and delineated neural and spinal cord invasion due to its excellent soft tissue contrast. In addition, severe osteolytic and osteoproliferative lesions identified by CT, combined with the strong contrast enhancement around the bony lesions observed on MRI images, strongly suggest a primary bone tumor rather than a tumor of muscular origin. These findings suggest that combining CT with MRI may provide more accurate diagnoses than using either modality alone in spinal chondrosarcoma.

The authors have no conflicting interests.

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Article

Case Report

J Vet Clin 2024; 41(2): 133-138

Published online April 30, 2024 https://doi.org/10.17555/jvc.2024.41.2.133

Copyright © The Korean Society of Veterinary Clinics.

Computed Tomography and Magnetic Resonance Imaging Features of Spinal Chondrosarcoma in a Cat

Minhee Lee1 , Sang-Kwon Lee1 , Juyoung Shin2 , Seulgi Bae2 , Kija Lee1,*

1Department of Veterinary Medical Imaging, College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea
2Department of Veterinary Internal Medicine, College of Veterinary Medicine, Kyungpook National University, Daegu 41566, Korea

Correspondence to:*leekj@knu.ac.kr

Received: February 26, 2024; Revised: March 29, 2024; Accepted: April 2, 2024

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

An 8-year-old, spayed female Persian cat weighing 3.6 kg presented with a lumbosacral mass and bilateral weight bearing hindlimb lameness. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed a dumbbell-shaped heterogeneous mass extending through the internal surface of the ileum and surrounding the lumbosacral junction. CT also revealed extensive osteoproliferation and bone lysis of the sacrum, but no evidence of any pulmonary metastasis. Furthermore, MRI revealed a focal area in the spinal cord showing connection with the adjacent tumor, suggesting tumor invasion into the spinal cord. Low-grade myxoid chondrosarcoma was histopathologically diagnosed. This is the first report describing CT and MRI findings of spinal cord chondrosarcoma in veterinary medicine. This study suggests that combining CT with MRI is a more sensitive tool for evaluating spinal tumors than using CT or MRI alone.

Keywords: feline, computed tomography, magnetic resonance imaging, spinal tumor, chondrosarcoma

Introduction

Chondrosarcoma is a rare spinal tumor in cats. Despite being the second most common type of primary bone tumors in dogs, only 0.3% of all feline malignant tumors were identified as chondrosarcoma in a retrospective study of 938 malignant feline tumors (16,17). In another retrospective study on 85 cats with tumors affecting the spinal cord, lymphoma and osteosarcoma were the most common tumors affecting the spinal cord, followed by glial tumors, meningioma, and fibrosarcoma, whereas chondrosarcoma accounts for only 1% of all feline spinal tumors (11). They usually originate in the bones and can affect the spinal cord either by compression or invasion, resulting in clinical signs of spinal cord dysfunction and pain.

The identification of the extent and origin of the tumor is essential for surgical or radiation therapy planning. In the diagnosis of spinal tumor, computed tomography (CT) is recommended for the evaluation of the bone structure and tumor metastasis whereas magnetic resonance imaging (MRI) is recommended for the accurate margin assessment of the tumor and diagnosis of tumor invasion into the spinal cord (3,15). However, studies on the CT and MRI features of spinal chondrosarcoma in dogs are scarce, and there are no reports on the imaging features of feline spinal chondrosarcoma. In a study conducted in dogs, the CT images of spinal chondrosarcomas revealed osteolytic and osteoproliferative lesions (15). Another study investigating spinal tumors in dogs and cats demonstrated that the spinal chondrosarcoma in dogs exhibited a mass with heterogeneous contrast enhancement on MRI (1). However, a comprehensive comparison of CT and MRI findings is lacking. We herein report a case of spinal chondrosarcoma in a cat and provide detailed insights into the CT and MRI findings.

Case Report

An 8-year-old, spayed female Persian cat (3.6 kg) presented with bilateral weight bearing hindlimb lameness. The owner noticed a palpable soft tissue mass in the lumbosacral junction 1 week ago. The patient exhibited right hind limb lameness approximately 6 months ago and left hindlimb lameness 1 week before the visit. There were no specific findings other than a slightly decreased general proprioception of the bilateral hindlimb in the physical and neurological examinations. On complete blood count and serum chemistry, only the blood glucose level was slightly elevated (glucose 182 mg/dL; normal range 71-148 mg/dL).

Abdominal radiograph revealed two soft tissue masses, one at the lumbosacral junction and the other in the retroperitoneum (Fig. 1A, B). Focal osteolysis of the seventh lumbar vertebra and osteoproliferation of the sacrum were also observed. Abdominal radiographs revealed no other abnormalities. On ultrasound, the masses in the lumbosacral junction and retroperitoneum had heterogeneously hypoechoic parenchyma surrounded by a well-defined margin (Fig. 1C, D). Further evaluation of the mass was impossible because of the acoustic shadowing by the near vertebral structures; therefore, CT and MRI were performed.

Figure 1. Radiographic (A, B) and ultrasonographic (C, D) images of the spinal masses of a cat in the present case. Soft tissue masses at the lumbosacral junction and retroperitoneum are identified (arrowheads). There is a focal osteolysis of the seventh lumbar vertebra and osteoproliferation of the sacrum (arrow). On the ultrasound, a mass at the lumbosacral junction (C) and a mass in the retroperitoneum (D) are observed. The masses have well-distinct margin with the surrounding tissue and had heterogeneously hypoechoic parenchyma.

CT was performed using a 32-multislice CT scanner (Alexion; Canon Medical Systems, Japan). General anesthesia was induced using 5 mg/kg propofol (Anepol; Hana Pharm, Korea) and maintained with 1.5-2.5% isoflurane (Isoflurane®; Choongwae Co., Ltd, Korea) and 1 L/min oxygen. The scanning parameters were as follows: 120 kV, 112 mA and 2.5-mm slice thickness with rotation time of 750 ms. The cat was positioned in sternal recumbency on the CT table, and thoracic and abdominal CT images were obtained. A contrast study was conducted after the intravenous administration of 600 mgI/kg iohexol (Omnipaque 300; GE Healthcare, Norway) injected at a speed of 1.5 mL/s using an autoinjector (A-60; Nemoto Kyorindo Co., Japan). Triple-phase CT images including arterial, venous, and delayed phases were obtained for abdominal CT whereas only delayed-phase images were obtained for thoracic CT. Postcontrast CT images of the artery, venous and delayed phase were obtained at 10, 45 and 100 s after injections. All CT data were cross-sectionally reconstructed in the transverse and sagittal planes at a slice thickness of 1.0 mm.

Abdominal CT revealed a single, large dumbbell-shaped mass in the lumbosacral region and retroperitoneum (Fig. 2). Notably, the mass showed a connection through the internal surface of the ileum (Fig. 2A). The mass showed mild peripheral rim enhancement and irregular contrast enhancement of the parenchyma, and a well-distinct margin with surrounding multifidus, lumbar, and gluteal muscles was observed (Fig. 2B). Extensive osteoproliferation and cortical bone lysis of the sacrum, and severe osteolysis of the vertebral body, pedicle, and transverse process of the seventh lumbar were observed (Fig. 2C, F). There was no evidence of distant metastasis to the abdominal lymph nodes. Thoracic CT showed no discernible evidence of pulmonary metastasis or thoracic lymph node enlargement.

Figure 2. Non-contrast (A, D) and venous phase (B, E) transverse CT with soft tissue window and bone window setting (C, F) transverse images in a cat with spinal chondrosarcoma. There is a dumbbell-shaped heterogeneously contrast-enhancing mass around the lumbosacral junction, connected through the internal surface of the ileum (A, B). Osteolysis (arrow) of the pedicle and transverse process of the seventh lumbar (C), and cortical bone lysis and osteoproliferation (arrowheads) of right wing of sacrum is observed (F).

MRI was performed using the 1.5T MR system (Signa explorer, GE healthcare; Waukesha, WI) for further evaluation of tumor invasion into the spinal cord. Under general anesthesia, the patient was positioned in dorsal recumbency, and the images were obtained with spin-echo sequences with a 16-channel flexible coil. T1-weighted (T1W) (TR = 649 ms and TE 11 ms, matrix size = 360 × 240), T2-weighted (T2W) (TR = 4,280 ms and TE = 102 ms, matrix size = 360 × 240), fat-suppressed T1W (TR = 604 ms and TE = 10 ms, matrix size = 288 × 224), and STIR T2W (TR = 6,812 ms and TE = 81, matrix size = 360 × 240) images of the caudal abdominal region were obtained. MR images were scanned in the transverse and sagittal planes, and gadoterate meglumine (ClariscanTM, GE healthcare, United States) was intravenously injected at a dose of 0.3 mL/kg for contrast study.

On MRI, a dumbbell-shaped mass heterogeneously hyperintense to the muscle on T2W images and isointense on T1W images was identified (Fig. 3A, B). A T2W hyperintense and T1W hypointense focal area in the spinal cord, showing connection with the adjacent mass, was identified, strongly suggesting tumor invasion into the spinal cord (Fig. 3A, C). The left sciatic nerve was clearly observed but not the right sciatic nerve; tumor invasion of the right sciatic nerve was also considered (Fig. 3D, F). Peripheral rim enhancement of the mass and strong contrast enhancement around the osteolytic and proliferative lesions was observed, suggesting primary bone tumors such as osteosarcoma, chondrosarcoma, fibrosarcoma, and undifferentiated sarcoma (Fig. 3F).

Figure 3. T2W (A, D), T1W (B, E) and post-contrast fat-suppressed T1W (C, F) magnetic resonance images in a cat with spinal chondrosarcoma. A dumbbell-shaped mass heterogeneously hyperintense to muscle on T2W images and isointense on T1W images is identified (A, B). T2W hyperintense, T1W hypointense focal area in the spinal cord, showing connection with the adjacent mass is identified (A-C, solid arrows). While the left sciatic nerve is observed in the inner side of the ilium (open arrows), the right sciatic nerve was not clearly observed (D, E). Peripheral rim sign (F, solid arrow) and septonodular enhancement (F, asterisk) is observed. Contrast enhancement (arrowheads) around the osteolytic and proliferative lesions is observed (F).

Based on the aforementioned CT and MRI findings, the primary bone tumor with adjacent invasion into the spinal cord and right sciatic nerve was at the top of the list of differential diagnosis. Soft tissue sarcoma or malignant nerve sheath tumor originating from the right sciatic nerve were also included in the differential diagnosis. A punch biopsy of the lumbosacral mass through a dorsal approach was conducted, and multinodular proliferation of mesenchymal cells embedded in a myxomatous to chondroid matrix was revealed (Fig. 4). The histopathologic diagnosis of the mass was myxoid chondrosarcoma. The patient was administered medicine for pain management but died 9 months after the diagnosis, following severe lethargy, dysuria, and dyschezia. An autopsy was not performed due to the owner’s refusal.

Figure 4. Histopathological findings from the mass around the sacrum in a cat. A mesenchymal neoplasm comprised of a multinodular proliferation of polyhedral to slightly fusiform mesenchymal cells embedded in a myxomatous to chondroid matrix is identified, which is consistent with a consistent with a myxoid chondrosarcoma. H&E stain, scale bar = 20 µm.

Discussion

Based on our review of the literature, this is the first report describing the CT and MRI features of spinal chondrosarcoma, a rare spinal tumor in cats. The combination of CT and MRI was useful in evaluating bony lesions, adjacent soft tissues, and spinal cord as well as pulmonary metastasis in a cat with spinal chondrosarcoma.

While a few studies have reported the MRI features of spinal chondrosarcoma in dogs (1,15), no studies describing the MRI features of spinal chondrosarcoma in cats were conducted. The MRI features of spinal chondrosarcomas include a mass with hyperintensity on T2W, iso- to hypointensity on T1W, and mixed osteolytic and proliferative lesions (1). Another study of vertebral chondrosarcoma conducted in six dogs reported that all of the osteolytic and proliferative lesions involved the dorsal compartments of the vertebrae, including spinous processes and lamina (15). In this study, the presence of osteolytic lesions of the L7 pedicle and transverse process as well as the signal intensity of the mass was consistent with that in previous studies. However, while a previous study reported mild to marked contrast enhancement of mass parenchyma and/or the tumor margin in spinal chondrosarcoma (15), in the present study, the mass parenchyma only exhibited mild septonodular enhancement corresponding to fibrovascular septation. Similarly, in humans, the characteristics of chondrosarcoma arising from the trunk and extremities are reported to include heterogeneous contrast enhancement of the mass parenchyma with peripheral rim signs and septonodular enhancement corresponding to fibrovascular septation (6,18). Despite the lack of general contrast enhancement in the mass parenchyma, the tumor’s similarity to human chondrosarcoma warranted its inclusion in the differential diagnosis list. In addition, in the present study, strong contrast enhancement was observed around the osteolytic and proliferative lesion of the sacrum, which differs from the observations of previous studies.

In general, CT is useful in the diagnosis of the bone lesion and pulmonary metastases in tumors, whereas MRI is a more accurate techniques for evaluating the mass itself. In our case, extensive osteoproliferation and cortical bone lysis of the sacrum, severe osteolysis of the vertebral body and pedicle and transverse process of the seventh lumbar were more accurately identified on CT images. Chondrosarcomas have a lower metastatic rate than the other primary bone tumors (5). In this case report, pulmonary metastasis of the tumor was not observed on CT. MRI is useful in assessing tumor margin, neural invasion, and spinal cord invasion owing to its ability to achieve excellent soft tissue contrast (1,15) In particular, in this case report, the abnormal findings of the sciatic nerve, which could indicate invasion into the sciatic nerve, were observed only through MRI. Furthermore, the order of the hindlimb lameness, starting from the right hindlimb and extending to the left, could be explained by the right sciatic nerve invasion identified in the MRI images.

On CT and MRI, the mass, which was thought to be two masses in the lumbosacral junction and retroperitoneum on radiograph and ultrasound, turned out to be a single, large dumbbell-shaped mass extending through the internal surface of the ileum. Dumbbell-shaped tumors of the spinal region refers to separate tumors that are connected by a portion of tumor tissue transversing the neural foramen and that inhabit two or separate regions, and are categorized into nine subtypes based on location (2,9). In our case, the mass involved extralaminal, extradural and paravertebral regions, consistent with type VI dumbbell tumor (2). Dumbbell-shaped tumors are typically relatively small (12), however, similar to our case, a giant dumbbell-shaped mass has been reported in human giant lumbar schwannoma (10). Typically, the primary differential diagnosis for dumbbell-shaped tumor is a nerve sheath tumor, such as schwannoma or neurofibroma (13). A case of a dumbbell-shaped malignant peripheral nerve sheath tumor was also reported in a dog (14). However, in the case, the dumbbell-shaped mass identified as chondrosarcoma through histopathologic examination. In addition, on MRI images, the mass had a distinct contrast enhancement around the osteolytic areas of the sacrum, indicating the high possibility of a primary bone tumor rather than soft tissue sarcoma. This case suggests that bone tumors and peripheral nerve sheath tumors should be considered in patients with a dumbbell-shaped masses.

Chondrosarcomas are histologically characterized by anaplastic cartilage cells forming a cartilaginous matrix (18). Chondroblastic osteosarcoma, a subtype of osteosarcoma, also contains an abundant chondroid matrix (8). This may result in similar features on conventional MRI, such as septonodular or peripheral rim signs, which are also detected in chondrosarcomas (18). However, osteosarcoma has a high possibility of metastasis; therefore, the treatment for chondroblastic osteosarcoma must include chemotherapy before or after the surgical excision, whereas chondrosarcoma treatment dose not require chemotherapy (18). Therefore, an accurate diagnosis between chondrosarcoma and chondroblastic osteosarcoma is essential.

In humans, there has been increasing number of studies on functional MRI in oncological imaging for the characterization of the tumor in recent years (7). In particular, diffusion-weighted imaging (DWI) is a promising tool for the characterization of lesions (4). It is also employed to evaluate treatment response after chemotherapy (7). DWI contributes to cellularity and the extracellular matrix, resulting in a low ADC value in malignant tumors and a high ADC value in chondrogenesis-related tumors (4). Therefore, higher minimum ADC values are obtained in chondrosarcoma than in chondroblastic osteosarcoma due to the osteoid matrix of osteosarcoma (4). Although DWI was not performed in the present study, based on previous studies (4,18) DWI may be useful for differentiation between chondrosarcoma and chondroblastic osteosarcoma in veterinary medicine.

In conclusion, spinal chondrosarcoma is a rare tumor in cats, and CT and MRI were instrumental in diagnosing the tumor in this case. The CT images were useful in excluding pulmonary metastases and identifying osteolysis and osteoproliferation but were limited in diagnosing spinal cord and neural structures. The MRI images provided precise tumor margins and delineated neural and spinal cord invasion due to its excellent soft tissue contrast. In addition, severe osteolytic and osteoproliferative lesions identified by CT, combined with the strong contrast enhancement around the bony lesions observed on MRI images, strongly suggest a primary bone tumor rather than a tumor of muscular origin. These findings suggest that combining CT with MRI may provide more accurate diagnoses than using either modality alone in spinal chondrosarcoma.

Conflicts of Interest

The authors have no conflicting interests.

Fig 1.

Figure 1.Radiographic (A, B) and ultrasonographic (C, D) images of the spinal masses of a cat in the present case. Soft tissue masses at the lumbosacral junction and retroperitoneum are identified (arrowheads). There is a focal osteolysis of the seventh lumbar vertebra and osteoproliferation of the sacrum (arrow). On the ultrasound, a mass at the lumbosacral junction (C) and a mass in the retroperitoneum (D) are observed. The masses have well-distinct margin with the surrounding tissue and had heterogeneously hypoechoic parenchyma.
Journal of Veterinary Clinics 2024; 41: 133-138https://doi.org/10.17555/jvc.2024.41.2.133

Fig 2.

Figure 2.Non-contrast (A, D) and venous phase (B, E) transverse CT with soft tissue window and bone window setting (C, F) transverse images in a cat with spinal chondrosarcoma. There is a dumbbell-shaped heterogeneously contrast-enhancing mass around the lumbosacral junction, connected through the internal surface of the ileum (A, B). Osteolysis (arrow) of the pedicle and transverse process of the seventh lumbar (C), and cortical bone lysis and osteoproliferation (arrowheads) of right wing of sacrum is observed (F).
Journal of Veterinary Clinics 2024; 41: 133-138https://doi.org/10.17555/jvc.2024.41.2.133

Fig 3.

Figure 3.T2W (A, D), T1W (B, E) and post-contrast fat-suppressed T1W (C, F) magnetic resonance images in a cat with spinal chondrosarcoma. A dumbbell-shaped mass heterogeneously hyperintense to muscle on T2W images and isointense on T1W images is identified (A, B). T2W hyperintense, T1W hypointense focal area in the spinal cord, showing connection with the adjacent mass is identified (A-C, solid arrows). While the left sciatic nerve is observed in the inner side of the ilium (open arrows), the right sciatic nerve was not clearly observed (D, E). Peripheral rim sign (F, solid arrow) and septonodular enhancement (F, asterisk) is observed. Contrast enhancement (arrowheads) around the osteolytic and proliferative lesions is observed (F).
Journal of Veterinary Clinics 2024; 41: 133-138https://doi.org/10.17555/jvc.2024.41.2.133

Fig 4.

Figure 4.Histopathological findings from the mass around the sacrum in a cat. A mesenchymal neoplasm comprised of a multinodular proliferation of polyhedral to slightly fusiform mesenchymal cells embedded in a myxomatous to chondroid matrix is identified, which is consistent with a consistent with a myxoid chondrosarcoma. H&E stain, scale bar = 20 µm.
Journal of Veterinary Clinics 2024; 41: 133-138https://doi.org/10.17555/jvc.2024.41.2.133

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Vol.41 No.2 April 2024

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