Solitary fibrous tumor (SFT) of the pineal region
The majority of tumors in the pineal region are pineal parenchymal neoplasms or germ cell origin (Zhang, 2010). SFT in the pineal region is extremely rare with only four cases reported in the literature to date (Zhang, 2010, Jang 2013, Wen, 2014), including an unusual example of composite tumor of low-grade astrocytoma with a component of anaplastic SFT (Jang 2013) (Table 1). The main differential diagnoses of intracranial SFT are fibrous meningiomas and hemangiopericytomas (HPC).
Homogeneous or heterogeneous intense enhancement on both CT and MRI on contrast administration is reported as the most prominent feature of SFT (Wang, 2013). The dural tail sign, which is highly suggestive of meningioma, is also seen in SFT (Wang, 2013).
The distinguishing feature of SFT from both fibrous meningiomas and HPC is their uniform, strong immunoreactivity for CD34, CD 99, vimentin and Bcl2. Reactions for EMA, S-100, smooth muscle actin, desmin and progesterone receptors are inconsistent, and most often negative (Fletcher et al, 2013). Furthermore, on ultrastructural examination, SFT cells have abundant endoplasmic reticulum and do not form desmosomal junctions seen in meningiomas (Zhang, 2010).
SFT and HPC were previously classified as separate entities in the 2007 WHO classification of central nervous system tumors. However, recent molecular studies on the NAB2-STAT6 fusion gene and nuclear STAT6 immunoreactivity in both SFT and HPC indicate that these lesions represent a spectrum of the same entity (Schweizer, 2013). SFT are usually benign and their behavior resembles that of the WHO grade I meningioma. Histologic malignancy in SFT is infrequent and more often observed to be focal rather than widespread patterns. Recently different variants of the NAB2-STAT6 fusion genes have been reported in SFT of soft tissue and have been observed to correlate with malignant histological findings (i.e., higher Ki-67 label index, higher mitotic rate and presence of nuclear atypia/pleomorphism) with associated biological aggressive behavior and shorter disease free survival (Schwiezer et al, 2013). HPC on the other hand are often predictably aggressive. HPC in the pineal region is also rare and to date, only 6 cases have been described. Combined, only ten SFT and HPC of the pineal region have been reported (Table 1).
Though the follow-up of patients with previously reported pineal region SFT has been short (i.e., 3-16 months), recurrence after treatment appears to be rare unless a significant residual is left or high-grade features are identified on histology. Generally, CNS SFT outside of the pineal region is favorable and the extent of resection is an important factor, which determines recurrence-free survival (Bruder, 2015). Though recurrence is rare after gross total resection, there have been reports of regrowth of residual tumor after subtotal removal despite subsequent radiotherapy (Bruder, 2015). Furthermore, the biology of SFT in the intracranial compartment is not completely understood. Though most are benign and completely cured by gross total resection (Tihan, 2003; Wen, 2014), there have been a few cases found to be locally recurrent or even metastatic to the extracranial locations, such as soft tissue, spine, lung and liver (Ogawa, 2004; Ng, 2000; Kim, 2004).
In summary, SFT of the pineal region are rare and though usually a slow growing low-grade tumor, it can exist as a more aggressive form behaving in a similar fashion to HPC or other malignant soft tissue tumors. With recent molecular analyses, it is now possible to re-classify SFT and HPC on a spectrum of the same entity.
Contributed by M. Michelle Kameda-Smith, Boleslaw Lach, Kesava Reddy