37‐Year‐Old Female with Intraventricular Mass

Clinical History and Imaging

A 37‐year‐old female presented with occipital headache, muscle weakness and paresthesia in the right limbs over 3 months. Magnetic resonance imaging showed a 5 cm solid, contrast‐enhancing mass in the left lateral ventricle and adjacent parietal white matter with midline shift, ventricular compression and hydrocephalus (Figure 1a). After surgical resection, she was submitted to radiation therapy for 4 months and did well for 3 years, when progressively growing thoracic wall nodules appeared. In the last 2 weeks she complained of paraparesis and hypoesthesia in the lower limbs. Computerized tomography showed lesions in the left clavicle and scapula, sternum and T11 vertebra, the latter causing spinal cord compression (Figure 1b). Laminectomy was followed by radiation therapy for the thoracic lesions and chemotherapy. The patient evolved with improvement of muscular strength and relapsing episodes of thoracic pain, controlled with medication. So far there is no radiological evidence of intracranial recurrence.

Figure 1.

 

Neuropathological Findings

Macroscopic and histologic features of the resected specimens (intracranial and vertebral) were essentially similar. Grossly, the masses were whitish and firm. On hematoxylin and eosin staining, the lesions were hypercellular and consisted of compactly arranged, spindled to oval cells supplied with thin‐walled branching vessels (Figures 1c and 2a). Mitoses (Figure 2a, inset) could reach 4 / 10 high‐power fields (hpf) in some areas. Nuclear atypia and necrosis were not identified. Reticulin stain highlighted a predominantly perivascular network, which also wrapped individual cells and small groups (Figure 2b). Immunoreactivity was diffuse for vimentin, CD34 (Figure 2c) and CD99 (Figure 2d); focal for Bcl‐2 and negative for GFAP, EMA, S‐100 protein, cytokeratins (AE1AE3), estrogen and progesterone receptors, muscle (1A4, HHF‐35, desmin) and neuroendocrine (CD56, synaptophysin, chromogranin) markers. Ki‐67 index was around 15%. What is your diagnosis?

Figure 2.

 

Diagnosis

Intracranial solitary fibrous tumor with atypical histologic features and distant bone metastases.

Discussion

Solitary fibrous tumor (SFT) of the central nervous system (CNS) is rare and classified as a mesenchymal, non‐meningothelial lesion 3. It would originate from CD34‐positive fibroblasts localized to the dura and perivascular connective tissue. Intraventricular tumors would derive from the mesenchymal component of the choroid plexus 1. In the CNS, SFT occurs in adults without gender predilection. Symptoms and signs are non‐specific and vary with tumor location. On neuroimaging, SFT is solid and shows diffuse enhancement. Dural attachment may be observed, however dural tail sign is not a feature. It may be mimicked by other discrete tumors, such as meningioma and hemangiopericytoma (HPC). Macroscopically, SFT is well circumscribed, solid, lobulated whitish mass. Local infiltration and necrosis may be found in aggressive lesions. Histologically, fusiform or ovoid cells with vesicular nuclei and scant cytoplasm occur in hypo‐ or hypercellular areas. Hyalinized and/or myxoid background may be found. Vascularization is variable and characterized by branching vessels, sometimes in staghorn‐like pattern. Nuclear pleomorphism, necrosis and mitoses are absent or rare. Classically, SFT is strongly and diffusely immunopositive for vimentin, CD34, CD99 and Bcl‐2. EMA, S‐100 protein and cytokeratins are negative. Ki‐67 index is often less than 2% 1, 4.

As regards differential diagnosis, most meningiomas show whorls and psammoma bodies. Such features are not prominent in the fibrous variant, which exhibits a spindled/storiform architecture. Unlike SFT, meningiomas are immunopositive for EMA and negative for CD34. Distinction between HPC and SFT may be difficult, as both show similar cytological and architectural findings, including staghorn‐like vessels. In fact, it is debatable whether SFT and HPC are distinct entities or ends of a spectrum 2, 4. Tumors showing no (or only focal) immunopositivity for CD34 are currently considered HPC, while those diffusely and strongly positive for CD34, as the case here reported, are diagnosed as SFT 1, 3, 4. Microscopic differentiation is relevant as HPC are WHO grade II (usual) or III (anaplastic) lesions tending to recur and/or metastasize more commonly than SFT. Even though the latter has not been assigned a WHO grading, it tends to behave as low grade tumor after total gross resection 1, 3.

Thus, our case illustrates an extremely rare presentation of an intracranial STF with atypical histologic features and distant bone metastases. The qualification of atypical is based on hypercellularity and mitotic index, according to a recent review 1. The authors found 220 cases of SFT of the CNS from 1996 to 2011, around 13% of which showed cytological atypia/pleomorphism, hypercellularity, >4 mitoses/10 hpf and/or necrosis. Such findings were associated with tumors that locally recurred and/or originated distant metastases. Only 5 were complicated by extracranial metastases, just one in bone. The prognostic significance of spontaneous necrosis, high MIB1 index (>5%) and brain invasion are as yet undetermined 1.