Less-Common Cranial Targets

1.The vascular skull-base tumor where SRS shines

Head-and-neck paragangliomas are highly vascular neuroendocrine tumors of the parasympathetic paraganglia. The carotid body tumor is the most common overall, followed by jugular, tympanic, and vagal paragangliomas; glomus jugulare and glomus tympanicum, which arise in the jugular foramen and temporal bone, are the ones neurosurgeons and radiosurgeons see most often. Most are indolent, but they are not uniformly nonsecretory or sporadic, and under the current WHO classification all paragangliomas are regarded as having metastatic potential, so "benign" describes behavior rather than a guaranteed category. The pretreatment workup should include biochemical testing for catecholamine excess, since a minority secrete, and referral for germline testing, since pathogenic variants in the succinate dehydrogenase (SDHx) genes are common and carry implications for relatives. Ga-68 DOTATATE PET/CT has higher detection rates than MRI and is the study of choice when multifocal or metastatic disease is a concern. Observation is reasonable for selected small, asymptomatic, stable lesions, particularly in older patients. When treatment is needed, radiosurgery achieves local control on the order of 90%+ with low rates of new cranial-nerve deficit at modest marginal doses (commonly ~13–16 Gy), as primary treatment or for residual/recurrent disease. The goal is durable growth arrest and function preservation, not necessarily radiographic disappearance.

2.Radioresistant tumors that need high dose

Clival/skull-base chordomas and chondrosarcomas are locally aggressive and relatively radioresistant, requiring high total doses for control. Management is maximal safe resection followed by high-dose radiotherapy, and because the required dose abuts the brainstem and optic apparatus, proton/particle therapy is frequently preferred for its dose-distribution advantage in dose escalation. Radiosurgery has a role as a boost or for small residual/recurrent disease at a safe distance from critical structures. Chondrosarcoma generally carries a better prognosis than chordoma. The key teaching point is that a tight single-fraction margin alone is usually inadequate for these radioresistant tumors: they are a dose-escalation problem.

3.Benign, often multiple, sometimes VHL

Hemangioblastomas: sporadic or part of von Hippel-Lindau disease: are benign, highly vascular tumors of the cerebellum, brainstem, and spinal cord, frequently multiple in VHL. Radiosurgery controls the solid tumor nodule and is especially useful for small, multiple, or surgically inaccessible (brainstem) lesions, sparing the patient repeated craniotomies. Margin doses are higher than for most benign tumors, typically 15–18 Gy, with reported series using a median near 18 Gy in VHL disease and 15 Gy in sporadic tumors. In the largest multi-institutional series, progression-free survival of treated tumors was 92% at 3 years, 89% at 5 years, and 79% at 10 years, with higher marginal dose, smaller volume, solid rather than cystic tumor, and VHL association all predicting better control. Its limitation is the cystic component: SRS treats the mural nodule but does not address an associated symptomatic cyst, which may still require drainage or resection.

In VHL the treated lesion is not the whole problem. Radiosurgery controls what it targets, but new hemangioblastomas continue to form, with a 5-year new-tumor rate near 39%, so lifelong imaging surveillance is required and repeat radiosurgery is expected rather than exceptional. A new CNS hemangioblastoma should prompt germline VHL testing and screening for renal cell carcinoma, pheochromocytoma, pancreatic neuroendocrine tumor, and retinal angioma. Systemic therapy has also entered this space: the HIF-2-alpha inhibitor belzutifan is approved for VHL-associated disease and produced objective responses in 44% of patients with VHL-associated CNS hemangioblastoma in a dedicated phase 2 cohort, which can defer or reduce the need for repeated local treatment. Long-term radiosurgery series have not shown malignant transformation, de novo malignancy, or accelerated new-tumor formation in VHL patients.

4.Ocular tumors and children

Uveal (choroidal) melanoma is managed within ocular oncology, where proton beam therapy and episcleral plaque brachytherapy are the established globe-conserving treatments; Gamma Knife/LINAC radiosurgery is an alternative at some centers for eye-preserving treatment of selected tumors. In pediatric patients, the long latency for late radiation effects (secondary malignancy, neurocognitive and endocrine sequelae) weighs heavily, so integral-dose-sparing proton therapy and fractionation are often favored over single-fraction photon SRS, and indications are individualized with particular caution. Other rare cranial targets (e.g., selected ependymomas, hemangiopericytoma/solitary fibrous tumor, recurrent gliomas) are handled case by case within multidisciplinary review.