Unique cytologic and imaging features of a lumbosacral oligodendroglioma in a cat

Abstract

A 12-y-old castrated male domestic longhaired cat had progressive paraparesis and neurolocalization of L4-S3. MRI revealed a circumscribed intradural-extraparenchymal mass from L5 to S1 that was T2 and short tau inversion recovery hyperintense and strongly contrast-enhancing. Cytologic interpretation of a blind fine-needle aspirate obtained through the L5-L6 space was a tumor of probable mesenchymal origin. A pair of suspect neoplastic cells was seen on a cytocentrifuged preparation of the atlanto-occipital CSF sample, despite a normal nucleated cell count (0 × 10⁶/L) and total protein (0.11 g/L) with only 3 RBCs × 10⁶/L. Clinical signs progressed despite increasing doses of prednisolone and cytarabine arabinoside. Repeat MRI on day 162 demonstrated tumor progression from L4 to Cd2 vertebral segments with intraparenchymal extension. Surgical tumor debulking was attempted, but an L4-S1 dorsal laminectomy revealed diffusely abnormal neuroparenchyma. Intraoperative cryosection favored lymphoma, and the cat was euthanized intraoperatively 163 d following presentation. Postmortem examination was performed, and the final diagnosis was a high-grade oligodendroglioma. This case illustrates the cytologic, cryosection, and MRI features of a unique clinical presentation of oligodendroglioma.

Keywords: CSF; MRI; cats; cryosection; cytology; histopathology; neurology; spinal; tumor.

Figure 1.

Progression of the lumbosacral neoplasm on MRI (A, B) and at postmortem examination (C). A. Sagittal T2-weighted images of the lumbosacral back at initial MRI (day 64). The neoplasm forms a T2 hyperintense, intradural-extraparenchymal mass centered at L6 and L7 that extends cranially to L5 and caudally to S1 as fimbriated projections. B. Sagittal T2-weighted images of the lumbosacral back at the 3-mo recheck (day 162). The intradural-extraparenchymal mass is larger and newly extends into the spinal cord parenchyma at L6 and L7, resembling an intraparenchymal mass. In addition, local extension of the tumor is over a wider area (L4–Cd2). At L4–L6, the cranial extension of the mass involves the meninges and surface of the spinal cord. C. Postmortem examination. Arising within the spinal cord at the level of L5–S1 is an irregularly bulging, invasive, smooth, white-to-tan mass (arrows). Bar = 2 cm.

Figure 2.

Representative photomicrographs of the fine-needle aspirate (FNA) of the lumbosacral mass (A, B) and cytocentrifuged smear prepared from the CSF (C). Wright stain. A. A highly cellular smear of neoplastic cells present individually and in small-to-moderately sized aggregates admixed with wispy magenta extracellular matrix. B. The neoplastic cells were oval-to-rarely stellate with a moderate N:C ratio and deep-blue grainy cytoplasm that often contained several small clear discrete vacuoles. Cell borders ranged from indistinct-to-distinct with blebbed margins. The nucleus was oval and paracentric-to-eccentric with coarsely clumped chromatin and an indistinct nucleolus. Anisocytosis and anisokaryosis were moderate. Two binucleate cells are shown in this image (arrowheads). Inset: 2 cells with associated extracellular matrix at higher magnification. C. A single pair of oval cells was present that were suspected to be neoplastic cells from the lumbosacral mass based on their similar morphologic appearance to cells in the FNA.

Figure 3.

Transverse section of the lumbar spinal mass, cryosection (A) and H&E (B, C). A. Sections reveal a mixed round- and spindle-cell population. Neoplastic cells have variable amounts of cytoplasm with round-to-ovoid nuclei, finely stippled chromatin, and an inapparent nucleolus. Atypia is moderate, and no mitotic figures are noted. B. Approximately 80% of the spinal cord is replaced by an unencapsulated neoplasm composed of sheets of neoplastic oligodendrocytes admixed with arcades of microvascular proliferation. C. Neoplastic oligodendrocytes are loosely embedded within a light mucinous matrix. Neoplastic astrocytes sometimes have gemistocytic differentiation. Arcades of microvascular proliferation randomly occur within sheets of the mixed neoplastic glial cell population (asterisks).