Page 301 - Canine Lameness

17.2 Neoplasia of pecific eeions 273

chondrosarcoma. Benign tumors and lesions include epithelial inclusion cyst, histiocytoma,
hemangiopericytoma, fibroma, sebaceous gland adenoma, keratoacanthoma, adnexal dyspla-
sia, follicular cyst, keratoma, hamartoma, plasmacytoma, trichoblastoma apocrine gland cyst,
basal cell epithelioma, fibroma, hemangioma, and sebaceous hyperplasia.
Although osteosarcoma distal to the antebrachiocarpal and tarsocrural joint occurs, it appears to
be rare (Gamblin et al. 1995). While the metacarpal or metatarsal bones are the most common
sites, there does not appear to be a predilection for the thoracic or pelvic limb. Treatment options
for malignant tumors of the pes and manus include digit amputation, partial foot amputation,
partial limb amputation with prosthesis, and full limb amputation. The type of surgery will depend
on size and location of the tumor. Non‐osseous malignant tumors can be treated with marginal
excision and adjuvant radiation therapy when amputation is not possible or allowed.

17.2.2 Carpal Region

The carpal region, and more specifically the distal radius, is one of the two most common anatomic
sites for osteosarcoma (Section 11.3.3). Osteosarcoma of the distal radius remains the most frequent
neoplastic cause of lameness in this region for large‐ and Giant‐breed dogs. Because of the paucity of
soft tissues around the distal aspect of the radius, particularly on the cranial surface, it is common for
owners and veterinarians to see a “swelling” or mass effect in that region when neoplasia is present.
This holds true for osseous (i.e. osteosarcoma; Figure 13.13) or soft tissue (such as soft tissue or joint
capsule tumors) swelling. Tumors of the joint capsule are uncommon in the carpal area, nonetheless
villonodular synovitis (Section 11.3.4), histiocytic sarcoma, and synovial cell sarcoma should all be
considered as differential diagnoses. Treatment of carpal region neoplasia depends on the specific
diagnosis and extent. Options include local excision, radiation therapy, full or partial limb amputation,
as well as a variety of limb‐sparing surgeries for primary bone tumors specific to the distal radius.

17.2.3 Elbow Region
Although osteosarcoma of the distal humerus, as well as of the proximal radius and ulna, occurs, it is
rare (Liptak et al. 2004) and the maxim, “osteosarcoma occurs away from the elbow” generally holds
true. Several other rare neoplastic conditions have been described for this region: primary osteosar-
coma of the synovium of the elbow has been reported in a Labrador Retriever and should be differenti-
ated from calcinosis circumscripta (Section 14.14.1). While tumors of the synovium typically display
lytic changes in the bones on “both sides” of the joint, radiographs of this case of osteosarcoma of the
joint capsule did not reveal periarticular bone lysis (Thamm et al. 2000). Additionally, the elbow is one
of the three most common joints to develop periarticular histiocytic sarcoma. Other reported types of
sarcomas originating from the synovium in canines include malignant fibrous histiocytoma, fibrosar-
coma, and undifferentiated sarcoma (Craig et al. 2002). Synovial osteochondromatosis with malignant
transformation to chondrosarcoma has also been reported in another Labrador Retriever (Aeffner
et al. 2012). Treatment of tumors of the elbow region is challenging due to the limited soft tissues and
therefore frequently requires full limb amputation for malignant tumors.

17.2.4 Shoulder Region

The shoulder region, and more specifically the proximal humerus, is one of the two most common
anatomic sites for osteosarcoma, making it a frequent cause of lameness in large‐ and Giant‐breed
dogs. In general, scapular tumors are uncommon but, when they do occur, they are most often