Disseminated anaplastic hemangiopericytoma WHO grade III / solitary fibrous tumor, cellular type
The latest WHO classification of tumors of the central nervous system still considers meningeal hemangiopericytoma (HPC) a member of the group of mesenchymal tumors of the central nervous system (1)(3). Nevertheless, currently most pathologists do not longer consider HPC a specific entity but rather a growth pattern shared by many different tumors (2). Accordingly, it has been argued that HPC should be classified as solitary fibrous tumor, cellular type (cSFT) (3) Intracranial location is a rarity, with HPC / cSFT representing less than 1% of all CNS tumors and less than 2% of all meningeal tumors (4) (3). They are most commonly found superficially and related to the meninges (3). Intraventricular location is extremely rare. The initial differential diagnoses for this type of intraventricular process included ependymoma, choroid plexus papilloma or ventricular meningioma.
The histological pattern of the tumors in both locations in this patient were remarkably similar featuring the characteristic pattern of a highly cellular tumor of jumbled or "chaotic" appearance of densely packed monotonous plump or spindle-shaped tumor cells together with numerous thin-walled hyalinized vessels of "staghorn"-appearance. In addition, a network of delicate reticulin fibers investing individual tumor cells was apparent. At this point, differential diagnosis included HPC / cSFT, SFT, fibrous type (fSFT), meningioma, gliosarcoma, and mesenchymal chondrosarcoma. Further immunohistochemical studies disclosed strong positivity for vimentin and CD177, while positivity for CD34 was only focally seen. This profile was considered highly characteristic for HPC / cSFT. Furthermore, meningioma was ruled out by the lack of whorls, nuclear inclusions, and psammoma bodies, as well as the rich reticulin fiber network and the negativity for EMA. Gliosarcomas are usually at least in some regions positive for GFAP. Mesenchymal chondrosarcoma is positive for CD99 and would have at least small islands of hyaline cartilage. A diagnosis of fSFT was finally dismissed due to only focal positivity for CD34. With regard to the significantly elevated mitotic activity with more than 5 mitotic figures in 10 adjacent high power fields, the presence of necrosis, and the high cellular density, the tumors in this patient were classified as anaplastic according to the WHO classification (1)
Approximately 29% of hemangiopericytomas are anaplastic (4). 5-year survival is about 93% overall with a wide range of reported median survival rates of 62-142 months in the anaplastic variant (1, 4, 6). Known risk factors for tumor recurrence in hemangiopericytoma are tumor size ? 6cm and non-skull base location (5). It has been reported that 36% of patients who died succumbed to CNS tumor burden and, as expected, high-grade tumors were found to recur 3-7 years earlier than low grade tumors (1, 6).
According to the literature, approximately one-quarter of the patients develop spinal metastases (1); metastases to other soft tissues or internal organs are more common (6). The occurrence of spinal metastasis after such a short interval highlights the aggressive nature of the anaplastic variant and raises the question whether early craniospinal imaging and radiation are warranted.
There is a paucity of data on hemorrhage rates and the propensity and mechanism in hemangiopericytoma remain to be elucidated (2). The present case is especially unusual in that tumor hemorrhage occurred twice, and was ultimately the cause of death. Most likely, the initial hemorrhage and the natural ensuing disintegration of the tumor within the ventricular system contributed to the rapid and extensive CSF dissemination.
Radiation has long been established as a solid therapy option, whereas chemotherapy has been discussed controversially (1, 4). Current treatment with radical excision combined with adjuvant radiation has shown the best survival rates and recurrence-free rates and can thus be viewed as the optimal treatment to date (5, 6).
In conclusion, these tumors, especially in the presence of hemorrhage, may need aggressive treatment, i.e. early craniospinal diagnosis and radiation, analog to high-risk medulloblastoma.
Contributed by Kara Leigh Krajewski, MD, Jakob Matschke, MD, Niklas Humke, MD, Wolfgang B÷rm, MD, Manfred Westphal, MD, Nils Ole Schmidt, MD