Spine tumors 4 – Intradural Extramedullary Lesions
Lesions that occur within the thecal sac are categorized as intradural extramedullary lesions. The vast majority of these lesions are tumors. The most common are schwannomas (and other nerve sheath tumors) and meningiomas, but there are others that include ependymoma, metastatic disease, and lymphoma. Also remember that the intradural extramedullary space contains cerebrospinal fluid (CSF), so any process that diffusely affects CSF can affect this space.
Peripheral nerve sheath tumors are a group of benign and malignant nerve tumors including schwannomas and neurofibromas. These can expand the neural foramen and usually have well defined margins. Schwannomas tend to enhance a lot while neurofibromas enhance less. Sarcoidosis is another common granulomatous disease that can affect the cord. The most common appearance is T2 abnormality within the cord with some enhancement. Enhancement is often along the surface of the cord.
Neurofibromatosis is a genetic syndrome with two types, type 1 and type 2. NF type 1 is characterized by multiple plexiform (involving more than one adjacent nerve root) neurofibromas. If neurofibromas increase in size rapidly, have necrosis, or cause pain, that can be a sign of malignant degeneration. NF type 2 is characterized by multiple masses including schwannomas, meningiomas, or ependymomas. NF type 2 is sometimes called MISME syndrome.
Schwannomas are probably the most common intradural extramedullary lesions. They are well defined lesions with avid enhancement. They often have central non-enhancement or cystic degeneration, but calcification or hemorrhage are less common.
Case 1 – Meningioma. Meningiomas are well demarcated intradural lesions which occur along the dura and deflect the spinal cord. They enhance avidly and usually don’t have necrosis. They frequently calcify, which you may appreciate more on CT. If they are more elongated and plaquelike they may be referred to as “en plaque” menigiomas. They can cross the dura and have components outside the dura as well.
Case 2 – Myxopapillary ependymoma. Myxopapillary ependymomas are relatively common tumors that occur around the conus and cauda equina. They usually enhance avidly. Necrosis or hemorrhage are more common than in schwannomas. They were previously grade 1 tumors but have been upgraded to grade 2 because they frequently recur.
Leptomeningeal metastases are a consideration anytime you see multiple intradural nodules. In adults, these are most commonly from the most common tumors such as melanoma, lung, and breat cancer. Lymphoma can also occur along the cauda equina. In pediatric patients you should also think about intracranial tumors that spread in the CSF, like medulloblastoma, pineal
Case 3 – Paraganglioma. Spinal paragangliomas are rare spine tumors that have a lot of abnormal surrounding vessels and are prone to hemorrhage. Think about them anytime you see an enhancing tumor in the spine with a lot of flow voids. The other thing you might think about is a hemangioblastoma, but they are more likely to be cystic.
Case 4 – Lipoma. Fat containing lesions along the conus are common and can be lipomas or dermoids. Clues are fat-suppression of FS images, chemical shift artifact, and fat density on CT. If it is thin and linear along the filum terminale, it is likely a benign fatty filum terminale.
Summary. Intradural extramedullary lesions are among the most common spinal lesions and it is important to have a clear differential when you see them.
The level of this lecture is appropriate for radiology residents, radiology fellows, and trainees in other specialties who have an interest in neuroradiology or may see patients with spine tumors.
Other videos on the spine tumor playlist are found here