Pulmonary metastasis from a World Health Organization grade I intracranial parasagittal meningioma: a case report

[...]contrary to this belief, one third of meningiomas with distant metastases originate from grade I tumours with 31% identified incidentally.1 In contrast, grade III lesions, which demonstrate overt aggressive behaviour, represent only 1% of meningiomas and account for 40% of documented metastases.1 The true incidence of metastatic meningiomas is unknown, but given the frequent occurrence of grade I tumours, that metastatic lesions are often asymptomatic and that routine whole-body imaging is seldom performed, the stated figure of 0.1% is likely an underestimation.1 In our case, the interval between primary resection and metastasis detection was 11 years, considerably longer than the cited median duration of 58 months (range, 4 months to 15 years), reflecting the slow-growing nature of grade I tumours.1 Three quarters of metastatic WHO grade I meningiomas involve a single organ, primarily the lung (42%) followed by the spine (12%), bone (10%), liver (10%), and cervical lymph nodes (10%).1 Although conventional histological studies such as the Ki-67 proliferation index have failed to identify a subgroup of meningiomas predisposed to metastasis, loss of heterozygosity of 1p, 9p, 14q and 22q may be characteristic of these lesions.2 Clinical risk factors for metastasis include repeated surgery, local recurrence and invasion of the dural venous sinuses.1 The non-collapsible and valve-less nature of the dural venous sinuses, such as the SSS, may permit seeding of tumour cells into the internal jugular vein and subsequently into the pulmonary microcirculation, an indication that tumour location is pivotal in determining haematogenous metastasis.1 Parasagittal meningiomas, comprising 20% to 34% of lesions, are perhaps most susceptible because of their propensity to invade the SSS, technically hindering their complete resection.3 4 Our case illustrates the importance of treating the SSS infiltrating portion of these tumours, but there is little consensus on the appropriate management strategy. When the posterior SSS is patent, prohibiting its ligation and excision, some neurosurgeons prefer subtotal resection followed by adjuvant radiosurgery or radiotherapy.3 Others advocate the more technically demanding surgical approach of gross total resection with sinus reconstruction, to spare the patient the long-term adverse effects of irradiation.4 Both strategies offer comparable tumour control rates although multimodality treatment may be associated with fewer procedu