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Spinal Cord Tumors

Spinal Cord Tumors

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Tumors of the Spinal Canal

Introduction

  • Here, we will learn the key tumors of the spinal canal.
    • Primary spinal cord tumors are one-tenth as common as primary brain tumors but vertebral metastases are extremely common: at autopsy, the majority of patients with lung, breast, and prostate tumors have vertebral METs.
  • From the outset, it helps to divide spinal cord tumors into their three major localizations:
    • Intramedullary, which are tumors that grow out of the spinal cord, itself; the spinal cord parenchyma.
    • Intradural extramedullary, which are tumors that grow from internal to the dura mater but external to the spinal cord, itself.
    • Extradural extramedullary, which grow from external to the dura mater (ie, the vertebrae) but can invade the spinal canal and compress the spinal cord.

Anatomy of the Spinal Canal

To best understand these spaces, let's review the anatomy of the spinal canal; indicate that we'll specify their spaces and the intervening layers.

  • Start with an axial view of the spinal canal.
    • Label posterior and anterior.
  • Draw truncated segments of the vertebral body (anteriorly) and vertebral arch (posteriorly) (See: Vertebral Column).
  • Next, within the spinal canal, draw the spinal cord and nerve roots in axial section.
  • First, show that dura mater forms a thick ring within the spinal canal.
  • On one side of the diagram, draw the dural root sheath (aka dural root sleeve), which is the dural investment that follows nerve roots into the intervertebral foramen.
    • Show that the dura mater transitions into the epineurium of the peripheral nerve.
  • On the other, dissect away the dura, so we can see the layers underneath; the arachnoid and pia mater, together, transition into perineurium (although intertextual variation exists regarding this point, and it often goes unmentioned in textbooks).
  • Next, draw the arachnoid mater internal to the dura mater.
    • Show that it runs underneath the dura (we lose sight of it under the dural root sheath).
  • Now, internal to it, draw the pia mater, which directly adheres to the spinal cord and nerve roots, so it takes the shape of those structures.
  • Next, show the intervening spaces:
    • The epidural space, which forms external to the dura mater, internal to the vertebral foramen.
    • The subdural space between the dura and arachnoid mater layers.
    • The subarachnoid space between the arachnoid and pia mater layers.

Simplified Anatomy

From this anatomy, we create a simplified diagram to generalize the spaces for tumors of the spinal canal.

  • Draw the spinal cord; label it as the site of intramedullary tumors.
    • Consider that the ependymal cells (which surround the central canal) and the astrocytic glial cells (of the white matter) derive the majority of these tumors.
  • Draw a ring of dura mater.
  • Indicate that internal to it are the intradural, extramedullary tumors and that external to it are the extradural, extramedullary tumors (namely, the vertebral metastases).

Spinal Canal Tumor Types

To solidify this understanding, draw examples of each.

  • First, draw an intramedullary spinal cord tumor.
  • Then, draw intradural, extramedullary spinal tumor that is compressing the exterior of the spinal cord but is internal to the dura mater.
  • Now, draw an extradural, extramedullary spinal tumor that compresses both the dura and the spinal cord.

Intramedullary Spinal Cord Tumors

First, let's address the intramedullary spinal cord tumors.

  • Indicate that these are typically gliomas.
    • Most commonly, they are ependymomas. Ependymomas comprise ~ 50% of intramedullary spinal cord tumors.

As a simple heuristic...

  • Indicate that the most common intramedullary spinal cord tumors in adults are:
  • Ependymomas
  • Astrocytomas
  • Whereas, in children they are:
    • Astrocytomas
    • Gangliogliomas
  • Rarely, these tumors are hemangioblastomas (~25% of the time, these are associated with von Hippel-Lindau syndrome).
  • And spinal cord metastases, which are represented by the most common form of CNS METs: lung, breast, and melanoma malignancies, as well as drop metastases from medulloblastoma, which typically arises from the midline cerebellum.

Intradural, Extramedullary Tumors

Now, the intradural, extramedullary tumors.

  • Indicate that these are primary peripheral nerve sheath tumors:
    • Schwannomas
    • Neurofibromas
    • See also Malignant Peripheral Nerve Sheath Tumor
  • Meningiomas
  • Filum ependymomas also rarely invade this space.
    • They are ependymal tumors of the cauda equina; the majority are myxopapillary, G1.
  • To understand the basic pathology of peripheral nerve sheath tumors, let's draw a slice through both a schwannoma and a neurofibroma.
  • First, show that schwannomas are benign, encapsulated tumors; they arise from a Schwann cell cylinder (the myelinating peripheral nerve cell) and grow within the parent nerve (ie, they do NOT infiltrate the surrounding tissue).
    • Consider that schwannomas commonly originate from CN 8, the vestibulocochlear nerve (called acoustic schwannoma or vestibular schwannoma) at the cerebellopontine angle or the dorsal (sensory) nerve roots.
  • Indicate that they have a biphasic appearance: Antoni A & B.
    • Antoni A regions are densely cellular and can comprise Verocay bodies. Think "A" for pAcked.
    • Antoni B regions comprise a less cellular, loose stroma with thin, wispy-appearing cells.
  • Next, show a neurofibroma with diffuse nerve expansion with abnormal twisting and lengthening of the nerve fibers, called dolioectasia.
  • On histopathological section, collagen bundles can form a "shredded-carrot" appearance.

Extradural, Extramedullary Tumors

See: Metastases
Lastly, the extradural extramedullary tumors.

Most commonly, these metastases are:

  • Breast, lung, prostate, and GI tumors.

Less commonly, these metastases are:

  • Kidney (renal cell), multiple myeloma, lymphoma, and thyroid tumors.
  • Non-metastatic extradural, extramedullary tumors are most often chordomas or sarcomas.

Metastatic Spread of Cancer to the Spine

Let's address some of the fundamentals of metastatic spread of cancer to the spine.

  • First, indicate that bone METs are often divided into osteoblastic (bone forming) versus osteolytic (bone thinning) lesions, to help with the radiographic determination of the cancer type.
  • Now, let's introduce a helpful mneomonic for key tumor metastases and color-code them based on whether they are blastic or lytic METs.
  • BLT with Mayonaise and a Kosher PickLe
    • B: Breast
    • L: Lung
    • T: Thyroid
    • M: Multiple Myeloma
    • K: Kidney (Renal cell)
    • P: Prostate
    • L: Lymphoma
    • Note that this acronym omits GI malignancies: Garnish.
  • Indicate the four main mechanisms of extension:
    • The most commonly discussed being venous spread
    • The others being arterial spread, and lymphatic spread, and direct extension (meaning direct erosion of mediastinal (ie, lung or breast) or retroperitoneal (ie, prostate) tumor into the spine.

So now, let's focus on the venous spread of tumor cells via Batson's plexus; we'll see that the majority of METs first seed the vertebral body at the thoracic level before they spread throughout it.

  • In axial view, draw the vertebral body, which is the disc-shaped weight-bearing portion of the vertebra.
  • Next, draw the vertebral arch.
  • Indicate that it encloses the vertebral foramen through which the spinal cord passes.
  • Show that the vertebral arch comprises (from anterior to posterior):
    • Paired pedicles, which abut the vertebral body,
    • Paired laminae, which meet medially at the:
    • Singular spinous process, which extends posteriorly; it serves as an attachment site for ligaments and muscles of the vertebral column.
  • Then, label the transverse processes to which trunk muscles and ligaments attach.
    Show that the center of the vertebral body comprises spongy bone whereas the periphery comprises compact bone.

Now, show the key venous supply of the spine.

  • Draw a cross-section through the vena cava, then the azygous vein, and show that the azygous vein passes as a lumbar radicular vein towards the posterior aspect of the body.
  • Along the posterior vertebral body, show that Batson's plexus (aka the internal vertebral venous plexus) supplies the posterior vertebral body.
    • It is a valveless plexus, thus increased vena cava pressure will produce backflow into Batson's plexus.
  • Now, draw a skull and then represent the length of the vertebral column.

Let's demarcate the vertebrae based on the highest to lowest frequency of spine metastases:

  • Thoracic is the primary site of ~ 70% of METs, primarily the lung and breast METs.
    • At the thoracic level, the azygous vein communicates with Baton's plexus.
  • Lumbar is the primary site of ~ 20% of METs, primarily the prostate METs.
    • At the lumbar level, the prostate drains via the prostate plexus.
  • Cervical is the site of ~ 10% of METs.
  • Indicate the sacrum, which rarely attracts METs.
    • Sacral METs are still more common than chordomas but indicate that chordoma is the most common primary tumor of the sacrum. Chordomas typically arise within the sacrum or the clivus, at the skull base.
  • Generalized skeletal METs can occur when the left-side of the heart, which receives blood from the lungs via the pulmonary vein, showers tumor cells throughout the spine in a non-segmental manner.

References

  • Argenziano, Giuseppe, Aimilios Lallas, Caterina Longo, Elvira Moscarella, Athanassios Kyrgidis, and Gerardo Ferrara. Cutaneous Melanoma: A Pocket Guide for Diagnosis and Management. Academic Press, 2017.
  • Campos, S., P. Davey, A. Hird, B. Pressnail, J. Bilbao, R.I. Aviv, S. Symons, et al. "Brain Metastasis from an Unknown Primary, or Primary Brain Tumour? A Diagnostic Dilemma." Current Oncology 16, no. 1 (January 2009): 62–66.
  • Dawes, Laughlin. "Vertebral Metastases | Radiology Reference Article | Radiopaedia.Org." Radiopaedia. Accessed August 26, 2018. https://radiopaedia.org/articles/vertebral-metastases.
  • DeAngelis, Lisa M., and Jerome B. Posner. Neurologic Complications of Cancer. Oxford University Press, 2008.
  • Dickman, Curtis A., and Michael G. Fehlings. Spinal Cord and Spinal Column Tumors: Principles and Practice. Thieme, 2011.
  • Klimo, Paul, and Meic H. Schmidt. "Surgical Management of Spinal Metastases." The Oncologist 9, no. 2 (April 1, 2004): 188–96. https://doi.org/10.1634/theoncologist.9-2-188.
  • Kumar, Naveen, Satheesha NAYAK B, Surekha Shetty, and Sn Somayaji. "Azygos Ladder and Looped Thoracic Duct – a Case Report." International Journal of Anatomical Variations 4, no. 1 (April 14, 2011). https://www.pulsus.com/abstract/azygos-ladder-and-looped-thoracic-duct--a-case-report-1564.html.
  • Manfrè, Luigi. Vertebral Lesions. Springer, 2017.
  • McLain, Robert F., Maurie Markman, Ronald M. Bukowski, Roger Macklis, and Edward C. Benzel. Cancer in the Spine: Comprehensive Care. Springer Science & Business Media, 2008.
  • McLendon, Roger E., Marc K. Rosenblum, and Darell D. Bigner. Russell & Rubinstein's Pathology of Tumors of the Nervous System 7Ed. CRC Press, 2006.
  • Niederhuber, John E., James O. Armitage, James H. Doroshow, Michael B. Kastan, and Joel E. Tepper. Abeloff's Clinical Oncology E-Book. Elsevier Health Sciences, 2013.
  • Payer, Sebastian, Klaus Christian Mende, Med Pract, Manfred Westphal, and Sven O. Eicker. "Intramedullary Spinal Cord Metastases: An Increasingly Common Diagnosis." Neurosurgical Focus 39, no. 2 (August 2015): E15. https://doi.org/10.3171/2015.5.FOCUS15149.
  • Samartzis, Dino, Christopher C. Gillis, Patrick Shih, John E. O'Toole, and Richard G. Fessler. "Intramedullary Spinal Cord Tumors: Part I—Epidemiology, Pathophysiology, and Diagnosis." Global Spine Journal 5, no. 5 (October 2015): 425–35. https://doi.org/10.1055/s-0035-1549029.
  • Samuels, Martin A., Allan H. Ropper, and Joshua Klein. Adams and Victor's Principles of Neurology 10th Edition. McGraw-Hill Education, 2014.
  • Schiff, David, Santosh Kesari, and Patrick C. Y. Wen. Cancer Neurology in Clinical Practice: Neurologic Complications of Cancer and Its Treatment. Springer Science & Business Media, 2008.
  • Tobin, Matthew K., Joseph R. Geraghty, Herbert H. Engelhard, Andreas A. Linninger, and Ankit I. Mehta. "Intramedullary Spinal Cord Tumors: A Review of Current and Future Treatment Strategies." Neurosurgical Focus 39, no. 2 (August 2015): E14. https://doi.org/10.3171/2015.5.FOCUS15158.