EE 137: MR Imaging Review of the Skull Base Foramina and Their Lesions Brandon W. Sur MD, MSE Department of Imaging Sciences University of Rochester Medical Center

Disclaimer The author has no financial disclosure or conflicts of interest with the presented material in this presentation.

Objectives Review anatomical location of the skull base foramina with CT images Review contents of each foramen Learn various lesions affecting each foramen with exemplary MR images.

Cribriform Plate Anatomy Contents Thin, horizontal bony plate with numerous foramina transmitting nerves Part of the ethmoid bone Bounded laterally by the lateral lamella Contents Olfactory bulbs/nerves Anterior ethmoidal artery (extradural)

Cribriform Plate A C B Lesions Meningioma Esthesioneuroblastoma Squamous cell carcinoma Lymphoma Melanoma Olfactory schwannoma Bony lesions: fibrous dysplasia, metastases Esthesioneuroblastoma: Axial (A), coronal (B), and sagittal (C) T1+C images show a heterogeneously enhancing mass in the nasal cavity destroying the cribriform plate and extending intracranially

Cribriform Plate D E F Lesions Meningioma Esthesioneuroblastoma Squamous cell carcinoma Lymphoma Melanoma Olfactory schwannoma Bony lesions: fibrous dysplasia, metastases Olfactory groove meningioma: Sagittal (D), axial (E) , and coronal (F) T1+C images show an intensely enhancing dural based mass within the olfactory groove.

Optic Canal Contents Anatomy Located in the posterior portion of the orbital roof Situated within the base of the lesser wing of the sphenoid bone Contents Optic nerve and its meninges Ophthalmic artery Central retinal vein Sympathetic nerve fibers

Optic Canal A Optic Glioma: Axial T2 (A) shows diffusely thickened right optic nerve in a patient with neurofibromatosis type I. Axial T1+C (B) shows no significant enhancement. Lesions Optic nerve glioma Meningioma Schwannoma Lymphomatous/leukemic infiltration Hemangioblastoma Cavernous hemangioma Sarcoidosis B

Optic Canal C Optic nerve sheath meningioma: Coronal (C) and axial (D) T1+C images show enhancement along the left optic nerve and extending into the optic canal. Lesions Optic nerve glioma Meningioma Schwannoma Lymphomatous/leukemic Hemangioblastoma Cavernous hemangioma Sarcoidosis D

Superior Orbital Fissure Anatomy Located between the lesser and greater wings of the sphenoid bone Pathway between the cavernous sinus and the apex of the orbit Contents Oculomotor nerve Trochlear nerve Abducens nerve Ophthalamic (V-1) nerve Ophthalmic veins Sympathetic nerve plexus Orbital branch of middle meningeal artery Recurrent branch of lacrimal artery Lesions Aneurysm Meningioma Pituitary tumors Craniopharyngioma Perineural spread of tumor Lymphoma Orbital varix

Inferior Orbital Fissure Contents Maxillary nerve Zygomatic nerve Orbital branches of pterygopalatine ganglion Infraorbital vessels; inferior ophthalmic veins Anatomy Located inferior to the superior orbital fissure Bounded superiorly by the greater wing of sphenoid, inferiorly by maxilla and orbital process of palatine bone, and laterally by the zygomatic bone. Lesions Meningioma Schwannoma Perineural spread of tumor

Foramen Rotundum Anatomy Contents Located at the anterior base of the greater wing of the sphenoid bone Runs laterally obliquely downward Contents Maxillary (V-2) nerve Artery of the foramen rotundum Emissary veins

Foramen Rotundum B A Lesions Schwannoma Meningioma Nasopharyngeal carcinoma Metastasis Perineural spread Nasopharyngeal Carcinoma: Coronal (A) and axial (B) T1+C images show an ill-defined, enhancing sinonasal mass extending through the right foramen rotundum.

Foramen Rotundum C D Lesions Schwannoma Meningioma Nasopharyngeal carcinoma Metastasis Perineural spread Skin Squamous Cell Carcinoma Metastasis: Coronal (C) and axial (D) T1+C images show enhancement along the left foramen rotundum.

Foramen Ovale Anatomy Contents Located at the posterior base of the greater wing of the sphenoid bone; posterolateral to the foramen rotundum Extracranial opening at the lateral pterygoid plate Contents Mandibular (V-3) nerve Accessory meningeal artery Emissary veins

Foramen Ovale A B Lesions Schwannoma Meningioma Neurofibroma Hemangiopericytoma Perineural spread of tumor Meningioma: Sagittal (A) and axial (B) T1+C images show a dural based enhancing mass extending through the right foramen ovale.

Foramen Spinosum Contents Lesions Anatomy Meningeal branch of mandibular (V-3) nerve Middle meningeal artery Lesions Perineural spread of tumor Metastasis Anatomy Situated in the greater wing of the sphenoid bone Located posterolateral to the foramen ovale

Foramen Lacerum Anatomy Contents Lesions Situated in the occipital bone Located between the occipital condyle and jugular tubercle Runs anterolaterally Contents Greater petrosal nerve Internal carotid artery overlies Lesions Perineural spread of tumor Metastasis

Stylomastoid Foramen Contents Anatomy Facial nerve Located in the temporal bone Termination of the facial canal Contents Facial nerve Styloidmastoid artery

Stylomastoid Foramen A C B Lesions Schwannoma Neurofibroma Adenoid cystic carcinoma: Coronal T1+C (C) image shows an enhancing right parotid gland mass extending intracranially through the stylomastoid foramen and destroying the temporal bone. Schwannoma: Axial (A) and coronal (B) T1+C images show enhancement along the facial canal and the stylomastoid foramen. Lesions Schwannoma Neurofibroma Perineural spread of tumor

Internal Auditory Canal Contents Facial nerve Vestibulocochlear nerves Labyrinthine artery Anatomy Located in the petrous part of the temporal bone Runs laterally

Internal Auditory Canal B Schwannoma: Axial (A) and coronal (B) T1+C images show a heterogeneous, enhancing mass in the left cerebellopontine angle involving the left internal auditory canal. Lesions Schwannoma Meningioma Epidermoid Arachnoid cyst

Internal Auditory Canal Lesions Schwannoma Meningioma Epidermoid Arachnoid cyst Bilateral Acoustic Neuromas: Axial (C) and coronal (D) T1+C images of neurofibromatosis type II patient show bilateral enhancing masses in the bilateral internal auditory canals.

Jugular Foramen Anatomy Contents Formed by the petrous part of the temporal bone and the occipital bone Two compartments divided by the jugular spine:smaller, anteromedial, “pars nervosa” and larger, posterolateral, “pars vascularis” Contents Glossopharyngeal nerve Inferior petrosal sinus Vagus nerve Spinal accessory nerves Internal jugular vein Ascending pharyngeal& occipital artery branches

Jugular Foramen A B Lesions Schwannoma Meningioma Glomus tumor Metastases Perineural spread of tumor Glomus Tumor: Coronal (A) and axial (B) T1+C images show a heterogeneous, enhancing mass within the left jugular foramen.

Jugular Foramen C E D Lesions Schwannoma Meningioma Glomus tumor Chondrosarcoma: Axial (C) and coronal (D) T2 images demonstrate a T2 hyperintense lesion in the left jugular foramen. Axial T1+C image (E) shows heterogeneous enhancement. D Lesions Schwannoma Meningioma Glomus tumor Metastases

Hypoglossal Canal Anatomy Contents Situated in the occipital bone Located between the occipital condyle and jugular tubercle Runs anterolaterally Contents Hypoglossal nerve Meningeal branch of ascending pharyngeal artery Emissary vein

Hypoglossal Canal A C B D Lesions Meningioma: Coronal T1+C (A) and axial T1+C (B) images show an enhancing, dural based mass occupying the foramen magnum and extending into the right hypoglossal canal. Schwannoma: Coronal T1+C (C) and axial T1+C (D) images show a dumbell-shpaed (not fully seen in these two images), enhancing mass within the right hypoglossal canal. B D Lesions Meningioma Schwannoma Persistent hypoglossal artery

Hypoglossal Canal G E F Lesions Persistent Hypoglossal Artery: Axial (E) and coronal (F) images of CT angiogram of the head show persistent hypoglossal artery within expanded left hypoglossal canal. G F Dissection of Persistent Hypoglossal Artery: Axial image of CT angiogram of the head/neck (G) shows dissection of the persistent hypoglossal artery within the left hypoglossal canal. Lesions Meningioma Schwannoma Persistent hypoglossal artery

Foramen Magnum Anatomy Contents Situated in the occipital bone A line drawn between the basion and opisthion defines the opening Contents Spinal cord; medulla oblongata and meninges Vertebral arteries Spinal arteries and nerves

Foramen Magnum A B D C Lesions Meningioma Schwannoma Chordoma Coronal (A), sagittal (B) and axial T1+C (C) images show an intensely enhancing, dural based mass occupying the foramen magnum. Schwannoma: Coronal T1+C (D) image of a patient with NF2 shows an enhancing mass within the foramen magnum extending down to the spinal canal. Lesions Meningioma Schwannoma Chordoma Neurofibroma

Conclusion Understanding of the anatomy of the skull base foramina, knowledge of the characteristic and differential imaging findings of disorders affecting them, and reviewing pertinent clinical history will allow radiologists to formulate accurate diagnoses and present appropriate differential diagnostic considerations.

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