MRI system: 1.5 T magnet (Magnetom EspreeTM, Siemens Medical Technologies, Malvern, PA)

Sequences (Brain):

• Sagittal T2-W turbo spin echo (TSE) images (TR 4270 ms, TE 102 ms, 3 mm slice thickness)
• Transverse T2-W TSE images (TR 3592 ms, TE 102 ms, 3 mm slice thickness)
• Transverse T1-W SE images (TR 310 ms, TE 12 ms, 3 mm slice thickness)
• Transverse fluid attenuated inversion recovery (FLAIR) images (TR 8000 ms, TE 84 ms, TI 2372 ms, 3 mm slice thickness)
• Transverse T2*-W gradient recalled echo (GRE) images (TR 939 ms, TE 26 ms, flip angle 20, 3 mm slice thickness)
• Post contrast images (0.2 ml/kg (0.1 μmol/kg) gadopentetate dimeglumine (Magnevist.) i.v.)
• T1-W SE images in transverse, dorsal and sagittal plane; dorsal images acquired with FatSat (TR 307-482 ms, TE 12 ms, 3 mm slice thickness)

In the suprasellar region, there is an approximately 2.5 x 2.1 x 2.2 cm lobulated and fairly well circumscribed mass, extending rostrally to the caudal aspect of the frontal lobes and dorsally to the rostral ventral margin of the lateral ventricles. The mass is of mixed intensity but mostly hyperintense on T2-weighted images, hypointense on T1-weighted images, remains hyperintense on FLAIR images, shows punctate susceptibility artifacts on T2*-weighted GRE images and displays strong mildly heterogeneous contrast enhancement. The mass appears to be invading rather than displacing brain parenchyma. There is mild perilesional diffuse T2 hyperintensity evident on T2-weighted and FLAIR images. Best seen on sagittal postcontrast images, the mass appears separate from the pituitary gland and the pituitary fossa.

Diagnosis

Large suprasellar mass with evidence of mild intralesional hemorrhage and perilesional edema.
Based on unusually craniodorsal extent of the lesion, apparent invasion rather than displacement of brain parenchyma, and visibility of a normal pituitary gland separate from the mass, an intra-axial neoplasm or an extra-axial neoplasm invading brain parenchyma is considered most likely. Consideration is given to glioma, round cell neoplasia (e.g., lymphoma) and uncommon tumor types such as craniopharyngioma and germ cell tumor.

Due to the poor prognosis the dog’s owners elected euthanasia. On post mortem examination there was a circular, tan, 2 cm diameter mass at the level of the pituitary gland which extended into the brain. The mass was soft, gelatinous, irregularly circular, pale tan, and well circumscribed.

Microscopic examination was consistent with a malignant mixed germ cell tumor (suprasellar germ cell tumor).

Pituitary macrotumors (adenomas or adenocarcinomas) are the most common mass lesions diagnosed in the sellar or suprasellar region in dogs (1). However, this was considered unlikely in this patient due to the cranial dorsal extent of the lesion, invasion rather than displacement of adjacent brain parenchyma, and visibility of a normal pituitary gland separate from the mass. Other masses which may occur in the sellar or suprasellar region and which may be difficult to distinguish from primary pituitary tumors include meningiomas, lymphoma, granular cell tumors, gliomatosis cerebri, very rare tumor types such craniopharyngiomas and germ cell tumors, and metastases to the pituitary gland (2-9). Germ cell tumors usually occur in the ovaries and testes; however, extragonadal germ cell tumors have also been reported. Intracranial germ cell tumors tend to localize in the suprasellar region of dogs as seen in this case (10, 11).

References

1. Pollard RE, Reilly CM, Uerling MR, Wood FD, Feldman EC. Cross-sectional imaging characteristics of pituitary adenomas, invasive adenomas and adenocarcinomas in dogs: 33 cases (1988-2006). J Vet Intern Med. 2010;24(1):160-5.

2. Bentley RT. Magnetic resonance imaging diagnosis of brain tumors in dogs. Vet J. 2015.

3. Wisner ER, Dickinson PJ, Higgins RJ. Magnetic resonance imaging features of canine intracranial neoplasia. Vet Radiol Ultrasound. 2011;52(1 Suppl 1):S52-61.

4. Wisner ER, Zwingenberger AL. Brain. In: Wisner ER, Zwingenberger AL, editors. Atlas of Small Animal CT and MRI. Ames: Wiley Blackwell; 2015. p. 153-278.

5. Nagata T, Nakayama H, Uchida K, Uetsuka K, Yasoshima A, Yasunaga S, et al. Two cases of feline malignant craniopharyngioma. Vet Pathol. 2005;42(5):663-5.

6. Gutierrez-Quintana R, Carrera I, Dobromylskyj M, Patterson-Kane J, Ortega M, Wessmann A. Pituitary metastasis of pancreatic origin in a dog presenting with acute-onset blindness. J Am Anim Hosp Assoc. 2013;49(6):403-6.

7. Tamura S, Tamura Y, Suzuoka N, Ohoka A, Hasegawa T, Uchida K. Multiple metastases of thyroid cancer in the cranium and pituitary gland in two dogs. J Small Anim Pract. 2007;48(4):237-9.

8. Palus V, Volk HA, Lamb CR, Targett MP, Cherubini GB. MRI features of CNS lymphoma in dogs and cats. Vet Radiol Ultrasound. 2012;53(1):44-9.

9. Anwer CC, Vernau KM, Higgins RJ, Dickinson PJ, Sturges BK, LeCouteur RA, et al. Magnetic resonance imaging features of intracranial granular cell tumors in six dogs. Vet Radiol Ultrasound. 2013;54(3):271-7.

10. Hare WR. Primary suprasellar germ cell tumor in a dog. J Am Vet Med Assoc. 1993;203(10):1432-3.

11. Valentine BA, Summers BA, de Lahunta A, White CL, 3rd, Kuhajda FP. Suprasellar germ cell tumors in the dog: a report of five cases and review of the literature. Acta Neuropathol. 1988;76(1):94-100.