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Tungsten (W) is a potential candidate for plasma facing materials (PFMs) of fusion reactor. The helium (He) produced in fusion reaction is insoluble and easy to gather and form to He bubbles in W, resulting in embrittlement and degradation of the performance of the W matrix. In this paper, based on molecular dynamics, the nucleation and growth of helium bubbles in the bulk and at ∑3[211](110) and ∑9[110](411) grain boundaries of W was studied. As a result, the growth mechanism of Helium bubbles at grain boundary of W was different from in bulk. Helium bubbles in bulk W grow up by extruding dislocation rings. The growth mechanism of helium bubbles at ∑3[211](110) grain boundary was as follows: Firstly, a small amount of W interstitial atoms were extruded and emitted. And then the 1/2\begin{document}$\left\langle {111} \right\rangle $\end{document} dislocation line was extruded. Finally, the 1/2\begin{document}$\left\langle {111} \right\rangle $\end{document} dislocation line would migrate along the direction of [111] of the grain boundary interface. Moreover, the emission of W interstitial atoms and dislocation extrusion of the helium bubble were not observed in our simulated time scale at the ∑9[110](411) grain boundary. Then we used the NEB method to calculate the diffusion barrier of self-gap atoms in the bulk and at ∑3[211](110) and ∑9[110](411) grain boundaries of W, which explained the simulation results. The migration energy barrier of W self-gap atoms in the bulk and at ∑3[211](110) grain boundary was only a few to a few millielectron volts. So as long as W self-gap atoms dissociated from the surface of the He bubble in the thermal relaxation process, they can be easily migrated out. However, The migration energy of the W self-gap atom at the ∑9[110](411) grain boundary can be from a few tenths to a few electron volts. Even during the thermal relaxation process, the W self-gap atoms dissociated from the surface of the He bubble. It was difficult for the W self-gap atoms migrated out. Finally, the correlation between He bubble size and stress released was given. Either in bulk or at ∑3[211](110) and ∑9[110](411) grain boundaries of W, after the pressure of the helium bubble becomes stable with time, the radius of the helium bubble would increase rapidly whenever the pressure dropped sharply. So there was a small step on the curve of the evolution of the radius of the helium bubble with time. Thus, helium bubbles in W could promote growth by releasing pressure intermittently.

Objective: To investigate the clinicopathological characteristics, prognosis, pathology, and differential diagnosis of LPM by analyzing our experience and reviewed relevant literature. We also postulated the necessity of postoperative adjuvant therapy. Methods: 19 patients with LPM underwent surgical treatment from 2007 through 2010 in our department. The clinical charts of the patients, including surgical, histological, and follow-up records, as well as imaging studies, were analyzed retrospectively. Other 43 cases searched from the literature were also included, so that 62 LPM cases were summarized and reviewed together. Results: The summarized 62 patients comprised 30 males and 31 females aged 9 years to 79 years (40.7±18.3 years). The most common locations were convexity, skull base, para-sagittal and cervical canal. Multiple or diffuse lesions were found in 8 cases. There were 13 patients had peripheral blood abnormalities (21%). One-third of the cases had moderate to severe peritumoral brain edema. Thirty-eight patients had total resection, 12 patients not specified while 12 received subtotal resection or only biopsy. MIB-1 was available in 24 cases and a third of them were higher than 3%. Follow-up more than 3 year was only completed in 19/62 cases. Seven cases suffered recurrence and two of them died after 2 years of operation. Conclusion: LPM is a very rare benign variant of intracranial meningioma. Both lesions and hematological abnormalities have a predilection for younger individuals. Preoperative diagnosis of this subtype of meningioma is still difficult. Surgical resection is the primary treatment option, and supportive care for those not totally removed is very important, because the recurrence rate for this subtype is rather low. However, the massive infiltration of lymphocytes and plasma cells in LPMs are still controversial and the long-term follow-ups are needed. Radiotherapy is not recommended, and hormonal or immune-inhibitor therapy might be helpful.