Page 82 - Feline diagnostic imaging

6.2 ­iseases oo the Feline rain 79

(a)

(b)

(c)
Figure 6.3 Sagittal ultrasound image of a 1‐month‐old male
domestic longhair cat with GM2 gangliosidosis (Sandhoff
disease). The rostral portion of the head is on the left. The cat
received an injection of adeno‐associated viral vectors
(expressing hexosaminidase) in the left cerebral lateral ventricle,
from which ultrasound images were taken. The tip of the needle
(arrows) is positioned in the lateral ventricle. Some hyperechoic
air can be seen in the lateral ventricle (arrowhead) secondary to
the injection. IA, interthalamic adhesion; S, splenial sulcus.
Figure 6.2 Spatial resolution issues are a challenge with feline Source: Images courtesy of Dr Douglas Martin, Scott‐Ritchey
spinal MRI owing to the small size of the spinal cord and limited Research Center, Auburn University.
tissue contributing to signal intensity. Low field MR units often
need to employ large fields of view (FOV) of the spine (a,b) to Meningiomas can have a radiographic manifestation,
have sufficient signal to produce an image. However, the lower which is unusual for primary nervous system tumors.
spatial resolution makes it challenging to diagnose the
compressive lesion at L4–5 on the sagittal image (arrow), even Specifically, calvarial hyperostosis occurs due to infiltra-
with the transverse image (b) through this disc (arrow). It could tion and/or expansion into or through the calvarial vault
be argued that higher resolution could have been acquired [11–13]. A rostrocaudal radiograph of the dorsal calvarial
based on the brightness in the discs, CSF, and fat regions. region can demonstrate asymmetric changes in the calvar-
(c) With a FOV focused on the lumbar spine and higher image
spatial resolution, as well as the use of a 1.5 T scanner, it is easy ial vault if the mass is located adjacent to this bone
to localize the extruded and compressive material at L5–6 contour.
(arrows). Source: Images courtesy of Dr Shannon P. Holmes, Both CT and MRI are primarily used for the diagnosis of
Animal Cross‐Sectional Imaging Specialists. feline meningiomas. The estimated accuracy of MRI in
diagnosing feline meningiomas is 96% but is unknown for
signs in order of frequency include altered consciousness, cir- CT [14]. These masses are typically distinctly and smoothly
cling, seizures, ataxia, and behavioral changes, as well as non- marginated [14,15]. In MRI images, a complex of signal
specific clinical signs of lethargy and inappetence/anorexia [6]. intensity features is attributed to meningiomas. The masses
Meningiomas account for 85% of primary intracranial neo- are typically iso‐ to hyperintense to gray matter in T2‐
plasia and 59% of all tumors associated with the brain [6]. weighted (T2W) images, iso‐ to hypointense on T1‐
Domestic shorthair cats are overrepresented and cats with weighted (T1W) images, and undergo moderate‐to‐marked
meningiomas are over the age of 9 years [6,8,9]. These are homogeneous contrast enhancement (Figure 6.4) [14–16].
extraaxial masses that arise from the dura mater. Rostrotentorial The extraaxial location of a mass can often be confirmed
locations are the most common, with the rostrotentorial menin- with enhancement of the thickened dura matter surround-
ges and tela choroidea being the most common sites [6,10]. ing the mass margins in postcontrast images, referred to as