Metastatic meningioma – A radiological conundrum

60-year-old female, presented with right pelvic pain and swelling past one month. She also complained of intermittent headaches with vomiting for one month. No neurocognitive impairment or family history of cancer. MRI pelvis was performed, and biopsy was done from sacroiliac lesion. Based on the histopathological findings, which revealed meningothelial tumour with fascicular and whorled pattern of cells with no nuclear atypia, MRI brain was performed for further evaluation.

Meningiomas are dural-based extraaxial masses, which are usually well defined circumscribed to lobular masses with broad base towards dura [1]. Adjacent bony hyperostosis on CT can be either reactive or due to bony invasion. Typical meningiomas are well-marginated with homogenous enhancement, whereas atypical and aggressive WHO grade 2 and 3 types show brain invasion, internal necrosis, and adjacent osseous destruction with perilesional brain oedema [2]. MRI pelvis revealed T2 intermediate, STIR hyperintense heterogeneously enhancing lesion seen involving right iliac bone, sacroiliac joint and sacrococcygeal vertebrae, encasing sciatic nerve and exiting right sacral nerve. There is infiltration of the right pyriformis muscle, iliacus and gluteus maximus muscles. On MRI brain, a large T1 isointense and T2 intermediate extraaxial homogenously enhancing lesion is seen along the convexity of right parietal lobe, displacing the cuneus, precuneus and lateral occipital gyrus in the supratentorial aspect. No perilesional neuroparenchymal oedema. Given the histopathology of the sacroiliac lesion and the imaging features of extraaxial mass, we considered this a case of benign metastasizing meningioma, of which very few cases have been reported in literature. Histopathology of the primary tumour revealed WHO grade I meningioma.

Background

Meningiomas are the most common non-glial brain tumours, with female predilection and usually occur in 5^th-7^th decade of life. They originate from arachnoid cap cells like meningothelial cells and other precursors. Most of them are sporadic; however, few of the cases are familial, post radiotherapy and neurofibromatosis type 2 (NF-2) associated. They are usually asymptomatic; however, involvement of adjacent venous sinuses mass effect can cause symptoms like headache, vomiting, and seizures. Even small meningiomas are typically followed with imaging due to their unpredictable growth trajectories; hormonal changes around menopause have been thought to contribute to some growth escalation [1]. Metastatic meningiomas are treated by surgical resection. However, newer approaches like Stereotactic body radiotherapy (SBRT) and radiopharmaceutical targeted therapy like Peptide receptor radionuclide therapy (PRRT) [3].

Imaging perspectives

MRI is the modality of choice for imaging. Meningiomas present with broad base towards dura, appear hypointense on T1, intermediate on T2 with homogenous post-contrast enhancement. Ancillary findings include calcifications, bony hyperostosis, which are better appreciated on Computed Tomography (CT). The atypical and aggressive variants account for about 15-20% cases, which can show aggressive features like adjacent sinus invasion, bony destruction, neuroparenchymal infiltration and metastases [4].

Outcome

• Meningiomas are usually slow-growing indolent benign tumours. In high-grade meningiomas, though rare, extracranial metastases have been reported in literature and have poor prognosis. Lungs are the most common site of metastases, followed by bones [5].
• Smaller lesions, asymptomatic subjects can be managed conservatively. Though surgical excision is the mainstay for symptomatic cases, atypical, recurrent and high-grade variants require multimodal management like radiotherapy and endovascular embolization for tumoral shrinkage [4]. Somatostatin receptor (SSTR) expression has been found in meningiomas irrespective of grade; hence, Lutetium 177 (177 Lu) dotatate, a theranostic radio-isotope, which is beta particle-emitting somatostatin analogue, has evolved as a promising treatment tool in such high-grade meningiomas [6].

Teaching points

• MRI is the modality of choice for evaluation of extraaxial tumours.
• Clinical, radiological and histopathological correlation is quintessential in these tumours for appropriate medical and surgical management.

All patient data have been completely anonymised throughout the entire manuscript and related files.