Isolated cerebellopontine angle metastasis from breast cancer: The added value of MR spectroscopy

Cerebellopontine angle (CPA) tumors are predominantly vestibular schwannomas and meningiomas; metastatic lesions in this location are rare, particularly in the absence of multiple brain metastases. We report the case of a 53-year-old woman with a history of invasive ductal carcinoma of the breast in HER2-positive metastatic relapse, in whom brain MRI revealed a single 28 × 24 mm mass in the right cerebellopontine angle. The lesion was isointense on T1- and T2-weighted images, contained fluid components, and showed restricted diffusion (ADC 0.64 × 10⁻³ mm²/s) with intense peripheral enhancement after gadolinium administration. MR spectroscopy demonstrated markedly elevated Cho/NAA (6.73) and Cho/Cr (5.72) ratios within the lesion, with a normal perilesional spectroscopic profile, favoring a secondary lesion and allowing the main differential diagnoses to be excluded without biopsy. The patient underwent stereotactic radiotherapy (30 Gy in 5 fractions), with significant regression of the lesion on follow-up MRI at five months. This case illustrates the role of MR spectroscopy in the non-invasive characterization of atypical cerebellopontine angle lesions.