Page 441 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 407

(sidebone). These stress fractures may be incomplete stage of laminitis were able to show loss of normal
162
or complete and are usually accompanied by extensively corium architecture, loss of lamellar architecture,
VetBooks.ir process and the ossified ungular cartilage. They are non­ lamellae, and focal areas of separation between the epi­
increased signal intensity in the dermis including in the
increased bone mineral density (sclerosis) of the palmar
dermal and dermal lamellae in the stratum lamellatum,
articular, simple, and non‐displaced fractures but fre­
quently involve the fossa of the collateral ligament of resulting in an increased ratio (>0.7) between the width
the DIP joint. They have a predictable proximodistal of the stratum lamellatum and the total dermal width
course with a palmar to dorsal and axial to abaxial ori­ (stratum lamellatum + stratum reticulare). Similar but
3
entation. Enlargement and signal abnormalities were more pronounced findings were seen in chronic lamini­
seen in the ipsilateral chondrocoronal, chondrosesa­ tis due to displacement of the distal phalanx with more
moidean, collateral sesamoidean, and collateral liga­ obvious separation between dermal and epidermal
ments of most horses and thought to contribute to the lamellae and the formation of a triangular wedge of
pain causing lameness. 162 lamellar regeneration. 89,118 Additional findings were cir­
cumscribed areas in the hoof wall of low intensity repre­
senting gas, circumscribed areas of high signal intensity
Lesions of the Ungular Cartilages
representing abscess formation, irregularity of the corti­
Primary injuries of unossified ungular cartilages and cal outline of the distal phalanx, increased osseous fluid
their related chondrocoronal and chondrosesamoidean palmar to the dorsal cortex of the distal phalanx, and
ligaments are uncommon. Diagnosis depends on MRI that increased size and number of vascular channels in the
reveals a markedly thickened, hypervascular cartilage with distal phalanx. 89,118
irregular contours and diffusely increased STIR signal Mild focal disruption of interlamellar alignment or
intensity. Occasionally the thickened, inflamed cartilage focally increased dermal fluid may be seen as an inciden­
45
may appear malaligned and displaced relative to its attach­ tal finding not related to lameness. Focal or linear hemo­
ment site on the palmar process of the distal phalanx. siderin accumulation in the dermis from old trauma may
Ossification of one or both cartilages of the foot is cause a signal void.
usually characterized by continuity of normal bone Space‐occupying masses in the stratum medium or
structure from the proximal portion of the palmar pro­ lamellatum of the hoof wall, containing a variable
cess through the ossified cartilage with a hypointense amount of keratin, may be a cause of lameness or an
outer rim of cortical bone surrounding a hyperintense incidental finding on MR images. MRI reveals a
spongiosa. However, trauma to an ossified cartilage may smoothly demarcated hoof wall lesion replacing the
result in increased bone mineral density (sclerosis) com­ normal architecture of the dermis of the hoof wall or
bined with focal or diffuse osseous fluid and is charac­ sole with deformity of the adjacent surface of the distal
terized by increased STIR signal and reduced T1 and T2 phalanx. The signal characteristics of these space‐occu­
signal either at the base of the ossified cartilage or at the pying masses vary from an area void of signal or with
junction between two separate centers of ossification. hypointense signal on any sequence to an area of het­
Increased mineralization may also be an incidental find­ erogeneous mixed signal intensity in T1‐ and T2*‐
ing but usually then without osseous fluid. Trauma to an weighted images and hypointensity in STIR sequences
ossified cartilage may be accompanied by thickening (Figure 3.234). 101,104,106 This signal variation is likely to
and signal abnormalities in the chondrosesamoidean reflect the degree of keratinization in the mass. While
and chondrocoronal ligaments. Collateral desmitis of true keratomas usually result in a well‐circumscribed
the DIP joint may also occur in conjunction with severe hypointense circular area protruding into the dermis
ossification of the collateral cartilages. 45,55,105 and osseous defect, the signal intensity of granulomas
Fracture results in a clear linear hyperintensity at the and fibrous or fibrovascular masses tends to be more
base of an ossified cartilage surrounded by osseous mode­ heterogeneous and mixed. 7,101,106 Adjacent intermediate
ling, including osseous fluid, although clear differentiation or high STIR signal intensity in the trabecular bone of
between trauma to the junction between separate centers the distal phalanx is indicative of reactive inflammatory
of ossification and a fracture is not always easy. 55,162 osteitis. The tomographic slicing produced by MRI has
Quittor or infection of an ungular cartilage is charac­ been useful for precise anatomical localization and sur­
terized by thickening of the infected cartilage and gical planning of hoof wall mass removal. 68,106
increased STIR signal. There may be evidence of fluid
tracts or fluid pooling with focal high or heterogeneous
T2 and STIR signal intensity within the cartilage and Puncture Wounds of the Sole
surrounding soft tissues. MRI examination may also MRI has been shown to be an excellent modality for
reveal variable involvement of other soft tissue and osse­ diagnosing penetrating foot injury in the horse. 20,92
ous structures of the foot in addition to infection of the Injuries from penetrating foreign objects in the foot
ungular cartilages. Preoperative MRI was shown to often result in focal areas of hypointense signal travers­
facilitate and guide the surgical approach to and postop­ ing the soft tissues on the palmar aspect of the foot in all
erative management of quittor in patients. 112 image sequences. Signal hypointensity of these tracts is
explained in acute stages as a signal void due to air or
ferrous material and in chronic stages due to hemosid­
Lesions of the Hoof Wall and Space Occupying Lesions
erin, which may persist indefinitely as a sign of previ­
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MRI has revealed soft tissue changes of the dorsal ous penetrating injury. In one large, retrospective study
hoof wall in acute and chronic phases of laminitis. 3,72,118 of horses with synovial sepsis following a penetrating
High‐field MR images (4.7 T) of the developmental injury, MRI was able to identify injury to the DDFT, the