IMAGING RECOMMENDATION FOR SKULL BASE AND TEMPORAL BONE TUMORS
The skull base is a complex osseous structure that serves as a conduit between the intracranial and extracranial compartments. It contains several neural foramina and fissures with traversing neurovascular structures 20. As in adults, there is a wide variety of benign and malignant skull base tumors that may occur in the pediatric population such as nerve sheath tumors, glomus tumors, RMS, Ewing sarcoma, olfactory neuroblastoma/esthesioneuroblastoma, chondrosarcoma and chordoma21-23. Systemic malignancies such as lymphoma, leukemia and especially LCH may involve the skull base.
Clinical presentation of children with skull base tumors varies with sub-location: anterior, middle versus posterior skull base. Children with anterior skull base mass lesions often present late and without distinction between neoplastic and non-neoplastic entities or between benign and malignant neoplasms. Nasal obstruction especially long term unilateral nasal obstruction, sinonasal pain, epistaxis, excessive lacrimation, anosmia and even visual changes may be presenting symptoms24. Tumors of the middle skull base may present with headache, hypothalamic-pituitary dysfunction, visual changes, facial dysesthesia and pain, deficits of CN III-XI, facial deformity and oropharyngeal obstruction. Finally, tumors of the posterior skull base present with headache, neck pain which may be from craniocervical instability, torticollis secondary to the craniocervical junction involvement, or cranial nerve dysfunction including visual abnormalities and dysphagia with involvement of the hypoglossal canal and jugular foramen25.
Temporal bone neoplasms in the pediatric population are exceedingly rare. These typically include RMS. Other sarcomas are rare. Systemic malignancies such as lymphoma, leukemia and especially LCH may involve the temporal bone. Patients typically present with signs and symptoms that mimic refractory and severe ear infection. Additionally, common presenting symptoms include hearing loss, otorrhea, otalgia, vertigo and headache. Facial weakness and diplopia may also occur. Extension of the mass to involve the orbital apex, cavernous sinus, hypoglossal canal and jugular foramina may produce additional cranial nerve dysfunction symptoms. Finally, with invasion of the dura, patients may present with CSF leakage and/or meningitis26.
Imaging in Skull Base and Temporal Bone Tumor Staging
Both CT and MRI play complementary roles for evaluation of skull base and temporal bone tumors at both diagnosis and follow up27,28. Similar to head and neck tumors in other subsites, goals of imaging are to evaluate the origin and the extent of the lesion as well as to differentiate between neoplastic and non-neoplastic entities or between benign and malignant neoplasms. Following initial diagnosis, staging evaluation typically occurs via the AJCC TNM classification system for select sites. Esthesioneuroblastoma staging may occur via the Kadish or modified Kadish staging or Dulgerov systems which require imaging assessment of regional tumor invasion such as paranasal sinuses, orbits, skull base, dural and brain involvement, as well as evaluation of co-existing nodal and distant metastases29. Note that a universally agreed upon staging system does not exist for temporal bone tumors other than RMS.
Staging of skull base and temporal bone RMS, like all other RMS in the head and neck, is via the IRSG staging system9.
Staging of skull base and temporal bone RMS is recommended via the IRSG staging system. (GRADE A, SOR 1.08, very strong recommendation)