History
A 7-year-old 35.0-kg (77.0-lb) sexually intact male Rottweiler was evaluated because of an 18-month duration of progressive lameness in the left pelvic limb. No history of trauma was reported. On examination, the dog had a grade 2 (on a scale of 0 to 5) lameness in the left pelvic limb when walking, severe muscle atrophy of the left pelvic limb, decreased range of motion in both hip joints, and crepitus in both elbow joints. The remainder of the examination was unremarkable. Results of a CBC and serum biochemical analyses indicated mild neutrophilia (9.7 × 103 neutrophils/μL; reference range, 2.7 × 103 to 9.4 × 103 neutrophils/μL), mild hypocalcemia (9.2 mg/dL; reference range, 9.3 to 11.4 mg/dL), and high alkaline phosphatase activity (266 U/L; reference range, 17 U/L to 111 U/L). Results of urinalysis and bacterial culture from urine were unremarkable. Pelvic limb radiography was performed (Figure 1).
Ventrodorsal radiographic view of both hip joints (A) and lateral radiographic view of the left hip joint (B) of a 7-year-old 35.0-kg (77.0-lb) sexually intact male Rottweiler that was evaluated because of an 18-month duration of progressive lameness in the left pelvic limb.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Ventrodorsal radiographic view of both hip joints (A) and lateral radiographic view of the left hip joint (B) of a 7-year-old 35.0-kg (77.0-lb) sexually intact male Rottweiler that was evaluated because of an 18-month duration of progressive lameness in the left pelvic limb.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Ventrodorsal radiographic view of both hip joints (A) and lateral radiographic view of the left hip joint (B) of a 7-year-old 35.0-kg (77.0-lb) sexually intact male Rottweiler that was evaluated because of an 18-month duration of progressive lameness in the left pelvic limb.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
On the ventrodorsal view of the hip joints in extension, patient positioning was mildly oblique. The left femur had multiple small, round, well-delineated areas of increased lucency with mildly sclerotic margins and reduced trabecular detail in the femoral head and neck and an ill-defined endosteal mineral opacity superimposed on the distal metaphysis (Figure 2). The left hip joint had incongruent joint spacing and poor coverage of the left femoral head by the dorsal acetabular rim; both of these findings were slightly more noticeable owing to obliquity of pelvic positioning. In addition, the left hip joint had a smoothly margined osteophyte, suggestive of chronicity, on the left cranial acetabular margin and an irregular circumferential osteophyte on the left femoral head. The amount of musculature evident radiographically was markedly less in the left pelvic limb, compared with the right, consistent with findings on physical examination. The right hip joint had slight incongruent spacing, with about 50% coverage of the femoral head by the dorsal acetabular rim. Cystic calculi were noticed in the urinary bladder.
Same images as in Figure 1. The left femoral head and neck have a moth-eaten appearance with round to irregular areas of increased radiolucency (solid black arrows; A and B). Moderate-to-severe osteophytosis (dashed black arrows; A and B) is evident in the left hip joint. An ill-defined endosteal mineral opacity (asterisk; B) is superimposed on the distal metaphysis of the left femur, and cystic calculi (solid white arrows; A and B) are present in the urinary bladder.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Same images as in Figure 1. The left femoral head and neck have a moth-eaten appearance with round to irregular areas of increased radiolucency (solid black arrows; A and B). Moderate-to-severe osteophytosis (dashed black arrows; A and B) is evident in the left hip joint. An ill-defined endosteal mineral opacity (asterisk; B) is superimposed on the distal metaphysis of the left femur, and cystic calculi (solid white arrows; A and B) are present in the urinary bladder.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Same images as in Figure 1. The left femoral head and neck have a moth-eaten appearance with round to irregular areas of increased radiolucency (solid black arrows; A and B). Moderate-to-severe osteophytosis (dashed black arrows; A and B) is evident in the left hip joint. An ill-defined endosteal mineral opacity (asterisk; B) is superimposed on the distal metaphysis of the left femur, and cystic calculi (solid white arrows; A and B) are present in the urinary bladder.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Our differential diagnoses for the monostotic and potentially aggressive bone lesion combined with severe osteoarthrosis in the left hip joint included cystic degenerative change, villonodular synovitis, chronic low-grade bacterial osteomyelitis, or less likely aggressive disease (eg, synovial cell sarcoma, osteosarcoma, or fungal osteomyelitis). Muscle wasting noticed in the left pelvic limb was suspected to have been caused by the abnormalities noticed in the left hip joint and not secondary to neurologic disease. Cystic calculi were incidental findings for which the owner declined diagnostic procedures. The ill-defined endosteal mineral opacity superimposed on the distal metaphysis of the left femur was also suspected to have been an incidental finding.
Computed tomography of the hip joints revealed many small, round regions of cortical bone lysis in the left femoral neck in the region of the insertion of the joint capsule (Figure 3). Each of these small lesions had a short zone of transition, sclerotic rim, and minimal cortical disruption, consistent with nonaggressive bone lesions. Osteophytes, consistent with severe degenerative joint disease, were also identified on CT.
Sequential transverse (A through C) and reconstructed dorsal (D) plane CT images of the left hip joint of the dog in Figures 1 and 2. In the neck of the femur are many small, round, cystic lucencies (solid arrows; A through D), each with a short zone of transition, sclerotic rim, and minimal cortical disruption, consistent with nonaggressive bone lesions. The cystic lucencies should not be confused with the trochanteric fossa (asterisk; D). Also evident are osteophytes (dashed arrows; A and B), consistent with severe degenerative joint disease. The dog's left is to the right of the images (bone algorithm [window level, 1,100 HU; window width, 4,500 HU] at 2.0-mm slice thickness). The transverse images are at the level of the cranial (A), mid (B), and caudal (C) aspects of the left acetabulum.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Sequential transverse (A through C) and reconstructed dorsal (D) plane CT images of the left hip joint of the dog in Figures 1 and 2. In the neck of the femur are many small, round, cystic lucencies (solid arrows; A through D), each with a short zone of transition, sclerotic rim, and minimal cortical disruption, consistent with nonaggressive bone lesions. The cystic lucencies should not be confused with the trochanteric fossa (asterisk; D). Also evident are osteophytes (dashed arrows; A and B), consistent with severe degenerative joint disease. The dog's left is to the right of the images (bone algorithm [window level, 1,100 HU; window width, 4,500 HU] at 2.0-mm slice thickness). The transverse images are at the level of the cranial (A), mid (B), and caudal (C) aspects of the left acetabulum.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Sequential transverse (A through C) and reconstructed dorsal (D) plane CT images of the left hip joint of the dog in Figures 1 and 2. In the neck of the femur are many small, round, cystic lucencies (solid arrows; A through D), each with a short zone of transition, sclerotic rim, and minimal cortical disruption, consistent with nonaggressive bone lesions. The cystic lucencies should not be confused with the trochanteric fossa (asterisk; D). Also evident are osteophytes (dashed arrows; A and B), consistent with severe degenerative joint disease. The dog's left is to the right of the images (bone algorithm [window level, 1,100 HU; window width, 4,500 HU] at 2.0-mm slice thickness). The transverse images are at the level of the cranial (A), mid (B), and caudal (C) aspects of the left acetabulum.
Citation: Journal of the American Veterinary Medical Association 256, 9; 10.2460/javma.256.9.977
Treatment and Outcome
An exploratory arthrotomy of the left hip joint was performed with a standard craniolateral approach. Severe osteophytosis and joint capsule thickening were noticed during surgery. A small amount of synovial fluid was aspirated from the left hip joint and submitted for anaerobic bacterial culture. Rongeurs were used to debride and collect osteophytes and fibrocartilage for histologic evaluation and bacterial culture. Needle core biopsy samples of the left femoral head and neck and a sharply excised biopsy sample of joint capsule were also obtained and submitted for histologic evaluation. The arthrotomy was completed routinely, and the dog was recovered from anesthesia without complication.
Histologic evaluation revealed moderate diffuse, chronic synovial hyperplasia with neutrophilic and lymphoplasmacytic synovitis, consistent with degenerative joint disease, with no evidence of neoplasia or villonodular changes. Evaluation of the core biopsy samples did not yield a histologically distinct cystic lesion; therefore, although no definitive underlying cause was identified, the areas of cortical bone lysis with mildly sclerotic rims evident with radiography and CT were suspected to have been secondary to degenerative joint disease. Bacterial cultures yielded no growth.
Because of financial constraints, the owner elected to wait 5 months before pursuing definitive treatment. Five months after the initial evaluation, the dog was returned for a recheck examination. The dog's clinical signs and radiographic findings for the left hip joint and pelvic limb were unchanged from the initial evaluation. A left total hip joint replacement was performed without complication. Because the dog also had a ruptured cranial cruciate ligament of the right pelvic limb, the dog later underwent tibial plateau leveling osteotomy for treatment. Twenty-one months later, the dog was examined elsewhere for an acute onset of paraparesis of unknown cause and was euthanized.
Discussion
Radiographic and CT findings of multifocal osteolysis in the dog of the present report prompted biopsy to rule out aggressive disease, even though findings of such distinct mildly sclerotic margins typically indicate benign conditions. Results of CT for the dog in the present report enhanced our confidence that the dog's lesions were benign given the lack of an associated soft tissue mass, minimal cortical destruction, and conspicuity of distinct sclerotic margins. Although core biopsy samples did not yield a histologically distinct cystic lesion and results of histologic evaluation were not definitive, results also did not indicate an aggressive neoplastic or infectious lesion. We therefore diagnosed presumptive degenerative subchondral cysts. Misdiagnosis of benign processes as malignancies has been described1; thus, care must be taken to prevent inappropriate management or euthanasia. The long history and lack of overt signs of pain in the dog of the present report were inconsistent with signs and signalments of dogs with common aggressive bone lesions.
Nonaggressive bone lesions are less common and are characterized by a short zone of transition, smooth periosteal reaction, and minimal cortical disruption. Differential diagnoses include degenerative joint disease (as was the case in the dog of the present report), villonodular synovitis, tenosynovitis, or hypertrophic osteodystrophy. Degenerative joint disease with subchondral cysts (also termed juxta-articular bone cysts, synovial cysts, or osseous cyst-like lesions)2 is well documented in humans3 and horses4 but is poorly understood in small animal medicine. Nonetheless, subchondral degenerative cysts can occur in the femoral head and are likely seen with some level of frequency by veterinary radiologists.5 The underlying cause of subchondral cysts in veterinary patients is debated and likely multifactorial.2 Future investigation regarding underlying cause and association with osteoarthritis in small animals is needed. Treatment of nonclinical subchondral bone cysts is not necessary; however, if the patient is lame, then management of the osteoarthritis and surgical treatment of the underlying disease (eg, cranial cruciate ligament tear or hip dysplasia) is warranted.6 Pathogenesis of the severe osteoarthrosis in the hip joint of the dog of the present report was unknown but may have been from asymmetric severity of dysplastic conformation or more likely previous trauma to that joint with concurrent bilateral mild hip dysplasia.
Aggressive bone lesions account for most lytic bone lesions in dogs and are characterized by permeative bone destruction, cortical disruption, a long zone of transition, and an interrupted, irregular periosteal reaction.5 In our experience, most aggressive bone lesions are neoplastic in origin. In addition to CT, which is helpful in characterizing bone lesions, as was the case in the dog of the present report, MRI could be considered for further distinguishing between malignant and benign lesions; however, MRI is more expensive and time-consuming. A recent study7 shows similar diagnostic accuracy between biopsy and fine-needle aspiration of bone lesions in dogs, with improved results when both techniques are done concurrently. Findings for the dog in the present report, however, highlighted the limitations of needle core biopsy samples in diagnosing nonaggressive bone lesions. Unfortunately, more aggressive biopsy, which may have isolated a distinct cystic lesion for histologic evaluation, was not advisable in weight bearing bones because of the risk of subsequent iatrogenic fracture.
References
1. Marti JM. Bilateral pigmented villonodular synovitis in a dog. J Small Anim Pract 1997;38:256–260.
2. Baird DK, Hathcock JT, Kincaid SA, et al. Low-field magnetic resonance imaging of early subchondral cyst-like lesions in induced cranial cruciate ligament deficient dogs. Vet Radiol Ultrasound 1998;39:167–173.
3. Chisholm KA, Gilchrist JM. The Charcot joint: a modern neurologic perspective. J Clin Neuromuscul Dis 2011;13:1–13.
4. McIlwraith CW. Subchondral bone cysts in the horse: aetiology, diagnosis and treatment options. Equine Vet Educ 2010;10:313–317.
5. Thrall DE. Radiographic features of bone tumors and bone infections in dogs and cats. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 7th ed. St Louis: Elsevier, 2017;390–402.
6. Towle HA, Breur GJ. Miscellaneous orthopedic conditions. In: Tobias KM, Johnston SA, eds. Veterinary surgery small animal. St Louis: Elsevier, 2012;1112–1126.
7. Sabattini S, Renzi A, Buracco P, et al. Comparative assessment of the accuracy of cytological and histologic biopsies in the diagnosis of canine bone lesions. J Vet Intern Med 2017;31:864–871.
