Foramen Magnum Mass



Foramen Magnum Mass


Karen L. Salzman, MD



DIFFERENTIAL DIAGNOSIS


Common



  • Acquired Tonsillar Herniation


  • Dolichoectasia (Vertebrobasilar)


  • Chiari 1


  • Chiari 2


  • Diffuse Astrocytoma, Low Grade


Less Common



  • Meningioma


  • Schwannoma


  • Ependymoma


  • Metastases, Intracranial, Other


  • Subependymoma


  • Hemangioblastoma


  • Intracranial Hypotension


  • Skull Base Masses



    • Chordoma, Clivus


    • Chondrosarcoma, Skull Base


    • Giant Invasive Pituitary Macroadenoma


Rare but Important



  • Epidermoid Cyst


  • Dermoid Cyst


  • Syringomyelia


  • Neurenteric Cyst


ESSENTIAL INFORMATION


Key Differential Diagnosis Issues



  • Foramen magnum (FM) is posterior skull base aperture in occipital bone



    • Transmits medulla oblongata, vertebral arteries & accessory nerves (CN11)


  • FM mass can be divided into intra-axial, extra-axial, & skull base masses


  • Cisterna magna is skull base cistern between medulla anteriorly & occiput posteriorly


Helpful Clues for Common Diagnoses



  • Acquired Tonsillar Herniation



    • Secondary to posterior fossa mass effect or severe hydrocephalus


    • Tonsils pushed inferiorly, impacted into FM


    • Cisterna magna obliterated


    • 4th ventricle may obstruct causing hydrocephalus


  • Dolichoectasia (Vertebrobasilar)



    • Dilated, ectatic vessels in older patient


    • Typically affects vertebrobasilar system


    • May mimic a FM mass


  • Chiari 1



    • Small posterior fossa, crowded FM


    • Low-lying, pointed cerebellar tonsils; > 5 mm below FM


  • Chiari 2



    • Complex malformation of hindbrain with lumbar myelomeningocele


    • Tissue herniates through FM behind upper cervical cord


    • Elongated, “straw-like” 4th ventricle


    • Associated with dural abnormalities, “beaked” tectum, “towering” cerebellum, dysgenic corpus callosum


  • Diffuse Astrocytoma, Low Grade



    • Primary astrocytic brain tumor with intrinsic tendency for malignant progression


    • 50% of brainstem “gliomas” are low-grade astrocytoma; occur in pons & medulla of children


    • T2 hyperintense mass; ± enhancement


Helpful Clues for Less Common Diagnoses



  • Meningioma



    • Extra-axial, enhancing, dural-based mass with dural “tails”


    • Often occur along clivus with extension through FM


  • Schwannoma



    • Benign encapsulated nerve sheath tumor composed of differentiated neoplastic Schwann cells


    • Enhancing extra-axial mass; T2 hyperintense


    • Often occur along cranial nerves at skull base with extension into FM


  • Ependymoma



    • Soft or “plastic” tumor, squeezes out through 4th ventricle foramina


    • 2/3 infratentorial, 4th ventricle


    • Heterogeneously enhancing 4th ventricle mass


  • Metastases, Intracranial, Other



    • Enhancing mass, usually multiple


    • Primary tumor typically known


  • Subependymoma



    • Rare, benign, well-differentiated, intraventricular, ependymal tumor


    • Intraventricular, inferior 4th ventricle typical (60%)


    • T2 hyperintense lobular mass


    • Usually middle-aged or elderly male



  • Hemangioblastoma



    • Posterior fossa mass with cyst, enhancing mural nodule (60%); 40% solid mass


    • 80% cerebellar hemispheres; 15% vermis, 5% medulla, 4th ventricle


    • Often extend through FM


  • Intracranial Hypotension



    • Brain descent with tonsillar herniation &/or “sagging midbrain” in 40-50%


    • Diffuse, intense dural enhancement 85%


    • Headache caused by reduced intracranial CSF pressure


  • Chordoma, Clivus



    • Rare malignant tumor arising from remnants of primitive notochord


    • Destructive, T2 hyperintense midline mass in clivus


    • May extend into FM


  • Chondrosarcoma, Skull Base



    • Chondroid malignancy of the skull base, typically centered on petro-occipital fissure


    • Chondroid matrix on CT 50%; > 50% bone destruction


    • T2 hyperintense mass, heterogeneous enhancement


    • May extend into FM from adjacent bone


  • Giant Invasive Pituitary Macroadenoma

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Aug 7, 2016 | Posted by in NEUROLOGY | Comments Off on Foramen Magnum Mass
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