A 43-year-old female presented with headaches and involuntary limb movements. Brain MRI showed a lobulated, enhancing extra-axial mass in the left parietal lobe with surrounding edema. Cerebral angiography revealed the tumor was primarily fed by the posterior division of the left middle meningeal artery. The patient underwent embolization followed by surgical resection of the mass. Pathology found features consistent with a hemangiopericytoma, a mesenchymal tumor that can recur and metastasize unlike meningiomas.

1. Harbor-UCLA Neuroradiology Case Conference Sahar Farzin, M.D. Department of Radiology Harbor-UCLA Medical Center Hien Huynh, M.D. Department of Pathology Harbor-UCLA Medical Center

2. History: 43 year-old female with 4 month history of headaches and progressive worsening involuntary limb movements

3. Brain MRI. Axial FLAIR sequence: Lobulated mass with isointense signal in the left paramedian parietal lobe. There is mass effect on the left lateral ventricle and splenium of corpus callosum, and surrounding vasogenic edema. The mass abuts the dura posteriorly. Pial vessels are interposed between the mass and brain parenchyma, suggestive of an extra-axial tumor. There are prominent flow voids, or vessels, in the posterior aspect of the mass.

4. Brain MRI. T1WI Pre- and Post-gadolineum: lobulated enhancing mass in the left paramedian parietal lobe with a small nonenhancing, hypointense area posteriorly. There are vascular flow voids seen interposed between the mass and the underlying brain parenchyma, suggestive of an extra-axial mass. There is mass effect on the left lateral ventricle and splenium of the corpus callosum. The mass abuts the dura posteriorly.

5. Axial T1WIs Post-Gadolineum

6. Coronal T2WI Brain MRI. Coronal T2WIs show the left parietal lobe extra-axial mass with isointense signal to the gray matter. The mass is surrounded by hyperintense or edematous parenchyma. A cleavage plane is visualized between the mass and the surrounding parenchyma. Prominent flow voids are noted in the superior aspect of the mass, consistent with enlarged vessels.

7. Sagital T1WIs Pre- and Post-Gadolineum Brain MRI. Sagital T1WIs Pre- and Post-Gadolineum demonstrate a posteriorly dural-based, extra-axial mass with avid enhancement. There is surrounding parenchymal edema.

10. Lateral Cerebral DSA Image: Left ICA Injection ECA Internal Maxillary Artery Superficial Temporal Artery Middle Meningeal Artery Posterior division of MMA Anterior division of MMA

11. Lateral Cerebral DSA Image: ECA Injection Superfical Temporal Artery Internal Maxillary Artery Middle Meningeal Artery Note the enlarged size of the Middle Meningeal Artery in comparison to the normal Superficial Temporal Artery.

12. Sequential Lateral DSA Images: Selective catheterization of Posterior Division of MMA Tumor blush is seen early on after visualization of the arterial feeders, and persists after arterial washout. There are enlarged dysplastic distal arterial feeders noted. Tumor blush Dysplastic enlarged arterial feeders

13. Sequential Lateral Cerebral DSA Images: Left Vertebral Artery Injection Vertebral Artery Branch from Vertebral A. Basilar A. Posterior Cerebral A. Terminal arterial feeders Tumor blush Left Vertebral Artery injection shows a small muscular branch coursing posteriorly to supply the tumor. (Minor supply).

15. Tumor Embolization with PVA Particles Catheter-directed injection of two vials of 300-500 micron polyvinyl alcohol (PVA) particles for embolization purposes. Above images show progressive stagnation of contrast within the main arterial pedicle suggestive of successful embolization. Microcatheter tip Stagnant contrast within arterial pedicle

16. DSA Images During Embolization Show Spontaneous Extravasation Sequential lateral DSA images during embolization show spontaneous contrast extravasation from one of the intratumoral vessels. Contrast extravasation Contrast extravasation

17. Immediate Follow-up DSA Image Immediately following the DSA images that showed extravasation these images were obtained. Again seen is stagnant flow within the main arterial feeder with no further evidence of extravasation.

19. CT Brain

21. Pathology

22. Hematoxylin-Eosin, 10x On low magnification, the tumor is seen as highly cellular with a pattern of dysarray.

23. Hematoxylin-Eosin, 20x Many of the cells are round and plump as seen here, though they can vary with a more elongated morphology. There is also scant cytoplasm and inconspicuous nucleoli.

24. Hematoxylin-Eosin, 10x There are focal areas of lower cellularity with necrosis.

25. Hematoxylin-Eosin, 20x Though much of the vasculature consists of slit-like spaces, larger vessels when branched can have a “staghorn” appearance as seen here.

26. CD34 Immunohistochemical Stain, 20x Scattered vascular spaces are positive for CD34 (seen as brown areas) . However, the tumor cells themselves in the picture are negative for CD34 (blue areas). In one-third of all cases of hemangiopericytomas, the tumor cells can be positive for CD34 in a patchy distribution.

27. M1B Immunohistochemical Stain, 20x M1B is a nuclear stain that is used as a marker for proliferative activity. The percent positivity for M1B, or proliferation index, is 10-20% in this case (seen as brown-staining nuclei in the picture).

28. EMA Immunohistochemical Stain, 20x The image shows that the tumor is negative for EMA (Epithelial Membrane Antigen). Hemangiopericytomas are mostly EMA negative though there may be weak, focal positivity. The differential diagnosis of a hemangiopericytoma includes a meningioma, which is EMA positive.