Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

544 Small Animal Radiolo g y and Ultrasono graphy
Fig. 4-89 A 6-month-old male Shetland Sheepdog with a congenital
anomaly of the right front limb. There were no clinical
signs associated with this deformity. There is a marked deformity
of the metacarpal and carpal bones. The distal row of
carpal bones is deformed. The third and fourth digits are separated,
with articulation of the fourth and fifth digits with the
ulnar and accessory carpal bones, and articulation of the first,
second, and third digits with the radial, second, and third carpal
bones. The lateral carpal bones appear to articulate with the
ulna and the medial carpal bones with the radius. Diagnosis:
Ectrodactyly. The left forelimb was normal.
a kitten and three dogs. 379-381 Radiographically, the bone density was normal. Multiple
healing fractures with active callus formation were noted.
O S T E O P E T R O S I S
Osteopetrosis is a rare, hereditary, familial, and congenital bone abnormality manifested by
a generalized increase in bone density, especially in subchondral bone, that involves the
axial and appendicular skeleton (Fig. 4-91). Cortical thickening and increased medullary
densities, or marble bone, will partially or completely obliterate the medullary canal. 382-384
Pathologic fractures may occur despite the markedly increased bone density. Clinical signs
may be related to the fractures or to an anemia that results from obliteration of the bone
marrow. 383-385
E O S I N O P H I L I C PA N O S T E I T I S A N D E N O S T O S I S
Panosteitis is a self-limiting bone disorder that causes lameness due to an acute onset of
long bone pain. 386-394 It most frequently affects large-breed dogs. Although mainly a
disease of the young, having been reported in dogs as young as 2 months, it does occasionally
affect older individuals up to 7 years of age. The acute lameness may undergo
spontaneous remission and may recur in the same limb or reappear in another limb.
Evidence of pain frequently can be elicited by applying direct pressure to the affected
bone.
The radiographic findings in panosteitis center on the nutrient foramina and involve
the diaphysis and metaphysis of the long bones. 386,387 Four radiographically distinct phases
have been described. The earliest phase reveals a zone of radiolucency at the nutrient foramen.
This is rarely identified clinically and usually requires a retrospective analysis. The
second phase begins with an increase in endosteal and medullary density; there is blurring
of the normal trabecular pattern. Contrast between the medulla and cortex is reduced
(Figs. 4-92 and 4-93). In the third phase, the radiodense areas tend to coalesce, become