FORAMEN MAGNUM
AND HIGH CERVICAL CORD

The Woman with Rotating Paralysis

CHITRA KUMAR, BA
DANIEL MCGOUGH, MS
JONATHAN A. FORBES, MD

The lowest part of the brainstem is a structure called the medulla oblongata. At the transition between skull and cervical spine, also known as the craniocervical junction, the medulla oblongata transitions into the high cervical spinal cord. Both the medulla oblangata and cervical spinal cord are comprised of intricate sensory and motor highways responsible for transmission of information from the brain to the extremities. The “highways” in both regions are densely packed—as an example, the cervical spinal cord is roughly the same size as the human thumb. It is therefore no surprise that tumors compressing these structures can cause catastrophic neurologic dysfunction.

Neurofibromas are one such type of tumor that sometimes result in compression of the high cervical spinal cord. Neurofibromas arise from the sheath of peripheral nerves. Importantly, the vast majority of these tumors are benign.¹ In many cases, neurofibromas are detected only after they have become large enough to compress neighboring neurologic structures.² Neurofibromas should be distinguished from schwannomas—a similar type of benign tumor that also arises from the peripheral nerve sheath.³ The differentiation between neurofibroma and schwannoma is particularly important when surgical management is considered. Schwannomas tend to “displace” the parent nerve bundle and can often be easily dissected from associated nervous structures. In contrast, neurofibromas often densely encase the associated peripheral nerve—placing this structure at increased risk when resection is chosen. As neurofibromas and schwannomas can have similar appearance on computerized tomography (CT) scans and magnetic resonance imaging (MRI), in many cases it can be difficult to differentiate between the two histopathologies prior to surgery.⁴ It is important to remember that a small percentage of nerve sheath tumors can be malignant—this determination, which can only be made after microscopic evaluation of tumor tissue has been performed by the pathology team, can be critically important for delivering an accurate prognosis and selecting appropriate therapy.

Both neurofibromas and schwannomas arise from the sheath of peripheral nerves. However, when the site of origin is close to the central nervous system, it is possible for tumor growth to result in progressive compression of the spinal cord. As tumors initially compress the spinal cord, patients will often first note difficulty with balance secondary to early dysfunction of the posterior columns. As the degree of impingement progresses, it is common for patients to note some element of weakness, reflecting increasing dysfunction of the corticospinal tracts. Of critical importance, the corticospinal tracts consists of axons that carry information essential to movement from the cerebral cortex to the anterior horn of the spinal cord. After these impulses reach the anterior horn, peripheral nerves subsequently shuttle this information to the extremities.⁵ Mild weakness secondary to early dys-function of the corticospinal tracts can resolve completely following tumor resection. In patients with profound weakness prior to surgery, it is often not possible to restore complete function following tumor resection. When the tumor in question causes impingement of the high cervical spinal cord close to the region of foramen magnum, it is possible for patients to suffer a “rotating paralysis”—as experienced by our patient Isabella,^* whose story we will discuss.

At 42 years of age, Isabella awoke one morning barely able to walk. This development was not surprising to her. Severe weakness predominantly involving the left side of her body had been getting worse for half a decade. Initially, she had noticed mild problems with balance. Soon after, she began to have trouble picking things up with her left hand. Around this time, she immigrated with her 9-year-old daughter from her home country of Honduras to the United States. It was following her arrival to the United States that Isabella began to notice that her left leg now appeared to be getting weaker. Weakness in her left arm had also clearly worsened—this extremity had become nearly useless for activities of daily living. As she tried to settle into her new job in the United States, Isabella found it challenging to manage her progressively worsening neurologic disability. She considered seeking medical advice, but as a Spanish-speaking immigrant with no health insurance and little in the way of a support system, she was hesitant to go to the hospital. The weakness on the left side of her body was getting worse. In addition, she had begun to note new weakness involving her right leg. Eventually, this progressed to involve her right arm as well. When she awoke one morning barely able to get out of bed, Isabella knew there was no other choice but to seek medical care.

In the emergency department, MRI scans of Isabella’s brain and cervical spine were obtained. MRI of the cervical spine revealed a large tumor near the craniocervical junction resulting in severe impingement of her spinal cord (Figure 4.1). The source of her progressive neurologic disability had been identified. Based on its appearance on the MRI, the radiologist suspected the tumor was of peripheral nerve sheath origin

In the hospital, Isabella was introduced to Dr. Jonathan Forbes, a neurosurgeon specializing in tumors of the cranial base. During the first consultation, a muscle strength grading scale was used to evaluate the weakness in Isabella’s extremities. This muscle strength grading scale ranges from zero to five, with a score of zero signifying a complete lack of muscle activation.⁶ While some of her muscles scored a three or four, her entire left leg, from knee to foot, had no muscle activation and was scored 0/5. Her disability had progressed to the point where she dragged her left leg when attempting to walk. Her movements were ataxic, uncoordinated, and extremely labored. With the help of a translator, Dr. Forbes explained to Isabella that all her symptoms, from the weakness in her extremities to her difficulty balancing while walking, were a result of spinal cord compression caused by the growing tumor. He described the nature of the tumor and how, without intervention, it would likely progress with time to take away all remaining function in her arms and legs and possibly even her ability to breathe. The best course of action would be to surgically remove the tumor. After discussing the risks and benefits with her family and healthcare team, Isabella elected to proceed with the surgery.

The surgery was performed with Isabella in the prone position. Blood pressure was carefully managed by the anesthesia team and neuro-monitoring was used to optimize safety. Following exposure and boney removal, Dr. Forbes meticulously dissected the tumor free from the spinal cord under magnification and removed it without complication. A tissue sample was sent to pathology, which confirmed the tumor was a benign neurofibroma. Isabella did extremely well following the surgery. Shortly after the procedure, she began to notice the strength in her extremities was improving. At her one-year follow-up visit with Dr. Forbes, she had regained a great deal of strength and was now able to ambulate without using a cane. Repeat MR imaging did not show any evidence of residual or recurrent tumor tissue (Figure 4.2); other images showed that her spinal column remained perfectly stable. At this visit, Isabella happily reported that she was now able to enjoy hikes and other outdoor activities with her young daughter for the first time in many years.

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* a pseudonym