Case of the month #3
by Antonio Melendez Lazo (DipECVCP)
A 10-year-old neutered male mixed-breed dog presented with a two-minute generalized tonic-clonic epileptic seizure, followed by aggression and weakness of the hind limbs in the post-ictal phase. Physical and neurological examinations were unremarkable. A complete blood test showed no abnormalities, and rectal diazepam was prescribed for future seizures. However, the dog experienced three more seizures at home and was brought to the emergency room. Upon admission, treatment with phenobarbital was initiated.
A CT scan revealed a frontal extraparenchymal lesion causing midline deviation and enhancement after contrast administration. Surgery was performed to remove the mass via transfrontal rhomboid craniotomy, and imprints were taken before submitting the sample for histopathological examination. What’s your diagnosis?
Figures 1 and 2. CT scan. Note the frontal extraparenchymal lesion with enhancement after contrast administration and midline deviation in figure 1.
Fig. 2A-D. Intracranial mass imprint. Romanowsky-type stain (Quick Panoptic), 10-50x.
Clinical and cytologic samples were compatible with meningoma.
Cytologic diagnosis of meningioma can be challenging to interpret due to the variety of histologic subtypes described. In this case, there is a population of cells arranged in variably cohesive aggregates with some individual cells that are round to elongated with wispy bluish cytoplasm. Nuclei are also round to oval with mild variation in size, finely stippled chromatin and sometimes single, small visible nucleoli. Whorl formation and pink intra- and intercellular material is sometimes seen.
Histopathology confirmed the diagnosis of meningioma, specifically the meningothelial subtype.
Meningiomas are the most common primary CNS tumors in dogs and cats. Intracranial meningiomas are typically solitary, slow-growing discrete masses arising from arachnoid meninges cells. While most exhibit benign behavior, they can cause neurological signs due to their space-occupying effects. Although a mixture of histologic subtypes is often present, meningiomas are graded according to the human WHO tumor grading system, based on the dominant histologic pattern observed, the presence of necrosis, and the mitotic rate.
Some cytologic features most commonly associated to specific subtypes include:
- Intranuclear pseudoinclusions (cytoplasmic invaginations) in meningothelial subtypes;
- Whorl formation in transitional subtypes;
- Psammoma bodies (mineralized structures) in psammomatous subtypes;
- Abundant background pink extracellular matrix material in chordoid subtypes.
Meningiomas can usually recognized based on their appearance alone, and additional tests such as immunohistochemistry and cerebrospinal fluid analysis often do not provide specific information.
Zimmerman, K.L., Bender, H.S., Boon, G.D. et al. (2000). A comparison of the cytologic and histologic features of meningiomas in four dogs. Vet Clin Pathol 29: 29–34.
Dickinson, P.J., Sturges, B.K., Kass, P.H., and LeCouteur, R.A. (2006). Characteristics of cisternal cerebrospinal fluid associated with intracranial meningiomas in dogs: 56 cases (1985–2004). J Am Vet Med Assoc 228: 564–567.
Petersen, S.A., Sturges, B.K., Dickinson, P.J. et al. (2008). Canine intraspinal meningiomas: imaging features, histopathologic classification, and long‐term outcome in 34 dogs. J Vet Intern Med 22: 946–953
Motta, L., Mandara, M.T., and Skerritt, G.C. (2012). Canine and feline intracranial meningiomas: an updated review. Vet J 192: 153–165