Page 341 - Atlas of Small Animal CT and MRI

Neoplasia 331

space distension, comparable to the “golf tee” sign Cerebrospinal fluid disseminated metastasis
described for conventional myelography (Figure Tumors arising within the subarachnoid space or intra­
3.4.15). 22,23 Using either imaging modality, localizing a cranial ventricular system will occasionally exfoliate
meningioma to the intradural–extramedullary compart­ cells that seed the spinal leptomeninges as metastatic
ment may not be possible when the tumor mass is large. deposits. Imaging features of CSF disseminated metas­
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tases are variable, and their appearance depends on
Peripheral nerve sheath tumor characteristics of the primary neoplasm (Figure 3.4.19).
The term peripheral nerve sheath tumor (PNST) includes
neoplasms that originate from Schwann cells, fibroblasts, Other neoplasms
or perineural cells. Because the terminology for this Neoplasms, such as lymphoma and histiocytic sarcoma,
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group of tumors has been inconsistent, we choose to use can be intradural–extramedullary but do not appear to
the all‐encompassing term PNST. Age of onset in dogs be as constrained by the meninges and can also simulta­
is reported to be bimodal, peaking at 2–3 years and neously be extradural and/or intramedullary. Round
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7–9 years, with no apparent breed predilection. Small cell tumors range from well defined to amorphous but
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PNSTs arising from nerve roots contained within the usually homogeneously contrast enhance. Other imaging
meninges and limited to an intradural–extramedullary features are variable (Figure 3.4.20).
distribution within the vertebral canal have CT and MR
imaging features similar to spinal meningiomas and
cannot be reliably differentiated from other intradural– Intramedullary neoplasia
extramedullary neoplasms (Figure 3.4.16). However, In a report of 53 dogs with intramedullary spinal cord
PNSTs are more likely to invade spinal cord parenchyma neoplasia, approximately two thirds of the tumors were of
and can also extend along peripheral nerves external to neuroepithelial origin. The remainder were metastatic
the vertebral canal, taking on a more tubular or lobular neoplasms, the most common of which were hemangio­
shape (Figure 3.4.17 and Chapter 3.6). sarcoma and transitional cell carcinoma. In this study,
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ependymoma was the most common neuroepithelial
Spinal cord nephroblastoma tumor, followed by astrocytoma. Dogs with primary
Spinal cord nephroblastoma (SCN) is an uncommon neo­ neoplasms were significantly younger than dogs with
plasm of young dogs (6 months to 4 years) that arises from metastatic disease (5.9 years vs. 10.8 years), and primary
transformed embryological renal tissue that is entrapped neoplasms were distributed in the cervical, caudal thoracic,
within the spinal dura matter during development. 21,27 and lumbar regions, while metastasis occurred predomi­
German Shepherd Dogs may be overrepresented, although nantly in the mid to caudal lumbar region. The imaging
total numbers reported to date are small. Most SCNs are appearance of intracranial neuroepithelial neoplasms is
located within the T9–L3 region of the vertebral column described in Chapter 2.8, and imaging features of primary
and are unencapsulated and intradural–extramedullary, spinal cord neoplasms are similar. Imaging features of
although invasion into spinal cord parenchyma occurs, metastatic neoplasms is more variable, and, particularly
which has been correlated with a poorer prognosis. 21,27 CT with hemangiosarcoma metastasis, the presence of
and MR imaging features are similar to those described hemorrhage may add to the complexity of the MR imaging
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for other intradural–extramedullary masses. An SCN characteristics. A common feature of all intramedullary
appears as a soft‐tissue attenuating mass on unenhanced neoplasms is the presence of an intraparenchymal mass
CT images and as a contrast‐filling defect on CT myelog­ that causes an increase in spinal cord diameter and annular
raphy. Spinal cord nephroblastomas are T1 iso‐ to mildly narrowing of the surrounding subarachnoid space. This
hyperintense, T2 hyperintense, and homogeneously appears as circumferential attenuation of the subarachnoid
enhance following intravenous contrast administration space on CT myelographic or T2 and STIR MR images
(Figure 3.4.18). (Figures 3.4.21, 3.4.22, 3.4.23).

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