Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 529
Fig. 4-72 A 2-year-old male Rottweiler had a bite wound on
his right foreleg 5 months previously. The wound had been
treated with antibiotics but the swelling recurred. On physical
examination the limb was swollen at the carpus and forearm,
and a draining tract was present. There is diffuse soft-tissue
swelling involving the right forelimb. There is bony proliferation
involving the distal one-third of the ulna. A central area of radiolucency
extends through the caudal ulnar cortex, or cloaca. The
bone proximal and distal to the area of radiolucency is dense.
Diagnosis: Chronic osteomyelitis. A sequestrum is not observed
in this case. This lesion responded to surgical curettage.
In young dogs, the entire diaphyseal cortex may develop into a large sequestrum.
Extensive, reactive periosteal proliferation will surround the dense cortical sequestrum.
Fortunately this lesion will respond to antibiotics, because removal of the sequestrum is
not possible.
An unusual sequestrum may be seen when a bone is penetrated by a pin used as a fixator.
The radiographic appearance of concentric zones of osteosclerosis and osteolucency
surrounding the bone defect caused by a pin has been called a ring sequestrum. 279 Although
infection is a likely cause in this situation, bone necrosis from the heat related to inserting
the pin must be considered also.
An unusual outcome of bacterial osteomyelitis is the formation of a chronic bone
(Brodie’s) abscess. 280,281 This is a chronic abscess of bone that is incarcerated by a wall of
granulation tissue and a fibrous capsule. The abscess becomes static and sterile.
Radiographically, a chronic bone abscess appears as a focal lucency surrounded by a zone
of mild to moderate sclerosis. 281
M YC O T I C A N D H I G H E R B AC T E R I A L O S T E O M Y E L I T I S
Coccidioidomycosis and blastomycosis account for the majority of cases of mycotic
osteomyelitis; however, infections due to histoplasmosis, aspergillosis, cryptococcosis, paecilomycosis,
nocardiosis, actinomycosis, and sporotrichosis have been reported (Figs. 4-73
to 4-77). 127,282-305 Mycotic osteomyelitis is most frequently polyostotic. The periosteal and
endosteal bony proliferation in mycotic infection usually is denser and more extensive than
that seen with bacterial osteomyelitis. However, some lesions associated with histoplasmosis
and other systemic mycoses have been predominately lytic (Fig. 4-78). 284,288
Sequestrum formation is uncommon. The differentiation between mycotic osteomyelitis
and neoplasia is aided by knowing the geographic distribution of mycotic diseases and that
young animals are affected more often than older animals.