Lipomatous hemangiopericytoma (Fat forming solitary fibrous tumor) associated with oncogenic osteomalacia.
Hemangiopericytomas are rare tumors that constitute about 0.4% of all CNS tumors . This entity was first described by Stout and Murray in 1942 (8). Hemangiopericytomas have been classified as a group of tumors which share a common hemangiopericytic growth pattern and are a distinct clinical and pathological entity from meningiomas. These are neoplasms of pericytes that form solid sheets and nests around irregularly formed vascular channels.
The present case has certain unusual features. The patient presented with intracranial bleed. Although hemangiopericytomas are highly vascular tumors, they predominantly present with mass effect and seizures. Bleed in tumor is very rare. Till date, only 8 cases of hemangiopericytoma have been reported that presented with intracranial bleed (4,6). These have presented in different forms as intraparenchymal, subdural or subarachnoid hemorrhage and a combination of these (6). Our patient presented with intraparenchymal, subarachnoid and intraventricular bleed. Though pre-operative embolization has been recommended for these vascular tumors, it is not possible in an emergency setting due to raised intracranial pressure. A staged approach can also be performed wherein evacuation of hematoma is done in first setting and tumor excised later after the patient's neurological condition improves (6).
The other unusual presenting feature was association with oncogenic osteomalacia. Our patient was diagnosed to have unexplained osteomalacia three years back and was on treatment for the same. Oncogenic osteomalacia is a paraneoplastic syndrome that is attributed to a humoral factor FGF-23 secreted by mesenchymal tumors that inhibits the renal absorption of phosphate in the proximal renal tubule (2). It leads to decreased serum phosphate levels and abnormal bone mineralization. Clinical features include adult onset bone pain, muscular weakness and multiple bone fractures. Diagnosis is generally delayed by few years due to indolent onset of symptoms. This entity is extremely rare with intracranial tumors. Removal of the tumor results in normalization of the calcium and phosphate levels.
The third unusual feature about the case was that the tumor revealed large areas of adipocytic differentiation. Lipomatous variant of hemangiopericytoma is quite rare and is alternatively known as fat forming variant of solitary fibrous tumor. It is very rare in intracranial location with only two cases reported till date. The first case was described in occipital region and the other case was reported to involve the parapharyngeal space, skull base and jugular foramen (1,7). It has been hypothesized that immature pericytes within the tumor may undergo adipocytic differentiation. However, this hypothesis is controversial due to the lack of intermediate and transitional cells exhibiting the features of both pericytes and adipocytes (3).
This tumor can closely mimic spindle cell lipoma or well differentiated liposarcoma and therefore should be differentiated from the two. Hemangiopericytomas are usually positive for CD34 unlike liposarcomas.
Treatment includes surgical excision of the tumor. Though hemangiopericytomas are more aggressive than meningiomas with higher incidence of recurrence, Lipomatous hemangiopericytoma is a more benign variant. However, few cases of malignant variant have also been reported in literature (5). The benign variant has good long term results with total excision.
At three months follow up, patient has recovered from the third nerve palsy. Her MRI at follow up shows a small residual tumor. Her serum phosphate and vitamin D levels have also returned to normal. She received gamma knife radiosurgery for the residual tumor and after one year of follow up patient has been asymptomatic.
Contributed by Hanni Gulwani, DNB, MRCPath, Nitin Garg, MS, MCh