To review the anatomy of the foramina of the skull base and demonstrate these on plain radiographic, CT and MR images. To provide a pictorial review of MR sequences and findings in patients with 1) lesions of the neurovascular contents of these foramina and 2) direct extension of skull base lesions to involve these foramina or perineural/direct spread of neoplastic/inflammatory conditions through the skull base foramina

Interpretion of images of the skull base is a difficult and daunting task due to the complexity of skull base anatomy. Appreciation of and accurate interpretation of abnormalities of the skull base, its foramina and their contents on MR is vital because 1)this area is difficult to assess clinically and 2)to enable early diagnosis of the existence and extension of neoplastic lesions so as to optimise patient outcome. Skull base foramina: Names & Contents: Nomenclature to be used to identiy the cranial nerves:

What to look for: Asymmetry of the bony dimensions of a foramen Loss of the normal fat within a foramen An abnormal mass within a foramen/fossa/canal Abnormal signal intensity of nerves/vessels within a foramen Abnormal enhancement within a foramen Sclerosis/erosion of bone adjacent to a foramen Perineural spread along cranial nerves Tumours which may metastasize in this manner: Adenoid cystic carcinoma Squamous cell carcinoma Basal cell carcinoma Lymphoma Melanoma Schwannoma Some infections (herpes zoster, actinomycosis, lyme disease) may also spread in this manner Pathology affecting...

The anatomy of the skull base is complex. Inflammatory, infectious and malignant conditions of the head and neck may extend into the skull through the foramina in the base of skull or may extend intracranially through direct invasion of the bones of the skull base. Cranial nerves and vessels passing through the skull base foramina may serve as conduits for the spread of disease. Thorough knowledge of skull base anatomy, pathology of the skull base and the MR sequences which demonstrate such pathology is important.

e-mail: [email protected] Specialist registrar at University College Hospital Galway

Neuroradiology The Requisites 2nd edn. Grossman RI, Yousem DM. Elsevier 2003. Imaging Atlas of Human Anatomy. 3rd edn. Weir J, Abrahams P. Elsevier 2003.