**8. Meningiomas**

Meningiomas are predominantly benign tumours in adults arising from the meningotheli‐ um of the arachnoid mater. Consequently, they occur at the brain surface—over the cerebral convexity, parafalcine region or along the skull base. Rarely, they can occur in intraventricu‐ lar or intraosseous locations. Meningiomas account for 20–25% of all intracranial neoplasms, with women affected more commonly than men. They are commonly associated with loss of heterozygosity of the long arm of chromosome 22.

On CT and MRI, meningiomas typically appear as rounded or ovoid avidly enhancing masses with dural tails at the tumour margins, variable compressive effect on adjacent brain paren‐ chyma (mainly depending on tumour size) and occasional hyperostosis of the adjacent skull.

Molecular imaging of meningiomas can be accurately performed using somatostatin ana‐ logue radiotracers [54] (**Figure 11**).

**Figure 11.** *Row A*: Fusion PET/CT shows a Ga-68 DOTATATE-avid focus directly adjacent to the right anterior clinoid process of the sphenoid bone. *Rows B and C*: Multiplanar MRI sequences show characteristic features of an intracranial meningioma on non-enhanced (*arrows*) and gadolinium-enhanced (*arrowheads*) imaging.

#### **8.1. Somatostatin analogue radiotracers**

Currently, the primary indication for using gallium-68 (Ga-68)-labelled somatostatin ana‐ logue radiotracers is for PET imaging of carcinoid and other NETs which usually express a high density of somatostatin receptors to which these peptides bind with high affinity [55]. Some non-NETs are also known to express somatostatin receptors, including meningiomas [56–58] which express all of the five somatostatin receptor (SSTR) subtypes but predominant‐ ly SSTR1 and SSTR2.

Traditional scintigraphic imaging of meningiomas utilised indium-111-labelled octreotide and single-photon emission computed tomography (SPECT). However, PET imaging with Ga-68 labelled somatostatin analogue radiotracers such as 1,4,7,10-tetraazacyclododecane-1,4,7,10 tetraacetic acid (DOTA)-Tyr3 -octreotate (TATE), DOTA-1-Nal3 -octreotide (NOC) and DOTA-Phe1 -Tyr3 -octreotide (TOC) offers superior count statistics and spatial resolution compared with SPECT. It also provides much higher target-to-background ratio of radiotracer uptake and more detailed tumour characterisation and has largely replaced octreotide SPECT imaging. This detailed spatial characterisation of meningiomas, when coupled with anatom‐ ical imaging by CT and MRI (in particular), allows for more accurate radiotherapy planning in patients with large, non-resectable tumours.

The demonstration of DOTATATE avidity in an intracranial lesion with only some features of meningioma on CT or MRI could permit differentiation of a meningioma from other tu‐ mours such as metastasis or craniopharyngioma, which can have a significant impact on clinical management.

There are also emerging data that DOTATATE uptake on PET improves diagnostic accuracy by delineating meningioma from tumour-free tissue [58] that can potentially enhance on CT and MRI especially in the setting of previous therapy.

FET PET in the late phase may be useful for the non-invasive grading of meningiomas [59].
