Treatment of Metastatic Spinal Disease; what the Radiologist needs to know

Abstract

Advancements in technology and multidisciplinary management have revolutionized the treatment of spinal metastases. Imaging plays a pivotal role in determining the treatment course for spinal metastases. This article aims to review the relevant imaging findings in spinal metastases from the perspective of the treating clinician, describe the various treatment options, and discuss factors influencing choice for each available treatment option. Cases that once required radical surgical resection or low-dose conventional external beam radiation therapy, or both, are now being managed with separation surgery, spine stereotactic radiosurgery/stereotactic body radiation therapy, or both, with decreased morbidity, improved local control, and more durable pain control. The primary focus in determining treatment choice is now on tumor control outcomes, treatment-related morbidity, and quality of life.

Introduction

Approximately 1.8 million people are diagnosed with cancer annually in the United States. ¹ Increased longevity of patients with cancer due to recent advances in systemic therapies has led to an increasing number of patients presenting with metastatic disease. Due to the highly vascular red marrow in adult vertebrae, the vertebral column is the most common site for skeletal metastatic disease. ^2,3 Overall, spinal metastases are the third most common site of metastatic disease following the lungs and liver. ^4–6 Approximately, 10% of all cancer patients will develop symptomatic spinal metastases at some point during their disease course. ^4,7–9

Spinal metastases most commonly occur in the thoracic spine, followed by the lumbar spine and sacrum. The cervical spine is the least common site of spinal metastatic disease. ^4,6,8 Although many patients with spinal metastases do not have symptoms, the proliferation of neoplastic tissue leads to a progression of structural disruption. This structural disruption can cause pain due to pathological fracture, instability pain, periosteal stretching, or neurogenic pain from direct compression. ^2,4 More importantly, spinal cord compression eventually occurs in 10% of patients with spinal metastases causing sensory/motor or sphincter dysfunction. ^4,5,7 Overall, symptomatic spinal metastases lead to diminished functional independence and poor quality of life.

In the past, metastatic spinal disease has been treated surgically, with conventional external beam radiation therapy (EBRT), or both. These therapies have their drawbacks, as aggressive surgical resection often results in significant patient morbidity. ^2,7 The therapeutic effects of conventional EBRT are usually delayed 10–14 days from the start of treatment with maximal benefits occurring 12–20 weeks after treatment. Additionally, EBRT achieves complete or partial pain relief in only 60% of patients, with a median duration of only 4 months. ⁷ Over the past two decades, many improved and targeted therapies have been developed to treat spinal metastatic disease with a focus on long-term local tumor control to improve patient functionality and quality of life. ^4–7 These therapies include stereotactic radiosurgery (SRS), spine separation surgery, stereotactic beam radiation therapy (SBRT), and percutaneous minimally invasive procedures such as vertebroplasty/kyphoplasty, percutaneous ablations, and pre-surgical endovascular embolization. In select groups of patients, targeted pain management techniques can be utilized including epidural steroid injections and spinal neurolysis. ^10,11 There is scarce evidence in the literature regarding the use of these techniques. In any event, epidural steroid injection and spinal neurolysis can relieve pain, but do not contribute to long-term tumor control. Given this multitude of treatment options and the varying degree of spinal metastatic disease, a multidisciplinary approach in treating spinal metastatic disease is paramount. ^5–7

As part of the multidisciplinary approach, it is essential for diagnostic radiologists to be familiar with these various treatment options and understand the role of imaging in the treatment algorithm. This review details the various treatment options available for spinal metastatic disease with a focus on the relevant imaging findings from the perspective of the treating clinician.

Diagnostic Imaging

Patients with suspected metastatic spinal disease receive radiological imaging for diagnosis and to assess the extent of disease. MRI is currently the best available imaging modality to evaluate metastatic spinal disease. ¹² Initial imaging assessment with MRI plays a crucial role in the diagnosis and initial evaluation of metastatic spinal disease. It is the best modality to assess for the presence of pathological fracture, bowing of the posterior cortex, epidural soft tissue, neurologic compression, and spinal cord edema. ¹² Although there is a lack of universal agreement on the MR protocol to optimize evaluation of metastatic spinal disease, complete studies of the spine, which include STIR (short tau inversion recovery), T2, & T ₁ weighted sagittal with T ₁- and/or T₂ weighted axial images are necessary for the detection of vertebral metastasis, epidural metastasis, and cord compression. ¹² Axial T₂ weighted images are particularly useful as these are required to assess epidural disease using the Bilsky epidural spinal cord compression (ESCC) grading system. ^5,7 Additionally, contrast-enhanced sequences are often added to the protocol. Contrast-enhanced sequences are particularly useful for improved lesion detection and evaluation for leptomeningeal enhancement. ¹³

Relevant imaging findings in spinal metastasis include the extent of spinal involvement (solitary vs multiple), level of involvement and location within the vertebral column, the type of lesion (lytic, blastic, or mixed), the degree of vertebral body involvement, involvement of the posterior elements, the presence or absence of pathological fracture including the degree of vertebral body collapse, presence or absence of epidural soft tissue and cord compression. Dynamic radiographs are also particularly useful in assessing the spine’s stability and are factored into the Spinal Instability Neoplastic Score (SINS), which is discussed in detail below. ^4,5,7

Utilizing MRI to assess for epidural soft tissue is particularly important in determining the optimal treatment for the patients. ^5,7 However, in patients who cannot undergo MRI, CT myelography can be especially helpful. CT gives excellent osseous delineation and can detect cortical destruction. CT myelography offers assessment of osseous integrity and assessment of the thecal sac contents. ¹⁴ Neuroradiologists play a crucial role here partly because everything in the epidural space may not be tumor. For example, retropulsion of bone, hardware, epidural venous plexus, and artifacts can be mistaken for soft tissue tumor by the untrained eye. ⁷

Patient Assessment

Spinal metastases most commonly present with back pain and are therefore easily missed in the early stages of the disease. Progression may lead to intractable pain, neurological compromise, and spinal instability. Despite significant advances in surgical and radiation treatment, any intervention for spinal metastases is considered palliative, ¹⁵ with the aim of relieving pain and improving quality of life. Because of this, deciding on the optimum treatment plan is often a complex and challenging process involving a large multidisciplinary team. One algorithm proposed by Spratt et al is outlined in Figure 1. ⁷

Figure 1.

Initial assement algorithm for patient with spinal metastases. KPS, Karnofsy Performance Status.

Linking back pain to metastatic disease can be difficult due to the myriad ways pain can present in these patients. Symptoms generally progress over the course of weeks to months and can be disproportionate to the size of the lesion or its bony involvement. Pain is often localized to a specific area and worsens with activity and pressure. These symptoms are likely caused by a combination of cytokine production from the tumor, weakened bone from tumor-induced osteolysis, and periosteal stretching due to an enlarging lesion. ³ Direct compression of spinal cord and/or nerve roots can result in non-localized pain due to radiculopathy. Separately, spinal instability and fractures secondary to metastatic lesions can cause debilitating pain with weight-bearing. ⁴ Understanding the underlying cause of pain can help the clinician choose treatment modalities which will be most effective. Estimation of a patient’s prognosis is vital in creating a risk–benefit assessment for a patient’s treatment plan. Clearly, aggressive intervention should be avoided in those with limited survival, and thus multiple scoring systems were created, including the Tomita score, ¹⁶ the Bauer score, ¹⁷ the Skeletal Oncology Research Group score, ¹⁸ and the Tokuhashi and revised Tokuhashi. ^19–21 While each system uses different parameters, common factors include primary tumor type, presence or absence of neurological deficit, general systemic condition of the patient, visceral metastases, and the number of spinal metastases. Tumor type and presence of visceral metastases being the strongest prognosticators. ^22,23 General condition as measured by Karnofsky Performance Status (KPS) ²⁴ and/or the Eastern Cooperative Oncology Group scale (ECOG) ²⁵ are key components of these scores, as patients with poor functional status (KPS ≤ 40 or ECOG ≥ 3) are less likely to have clinically significant benefit from aggressive management such as surgery or stereotactic radiation compared to more conservative measures. ^7,26

While the Tomita and Tokuhashi scores are the most widely used, these aging scoring systems do not account for the improved survival of many cancer types and the improvements in radiation and surgical techniques, lowering the risks of treatment. ²¹ Newer models such as the Skeletal Oncology Research Group scale use machine learning algorithms to choose prognosticating variables and include laboratory values such as white cell count and hemoglobin levels ¹⁸ to more accurately predict survival and the likely benefit of intervention.

Nevertheless, these scoring systems provide a foundation for treatment decisions. Aggressive treatment was traditionally avoided in patients with less than 6 month survival, but as surgical and radiation treatments become less morbid and new systemic treatments become more effective, this algorithm will continue to evolve. ²⁶

Multidisciplinary Approach

Broadly, the different categories of treatment can be divided into systemic therapy, surgical management, conventional EBRT, SBRT/SRS, and percutaneous minimally invasive neurointerventional procedures (i.e. vertebroplasty, percutaneous ablations, and endovascular embolization). The specific indications and examples for each therapeutic option are discussed in more detail below. In general, each therapy has different indications, which are outlined in Table 1. Given the broad spectrum of treatment options provided by different clinical specialties or a combination of specialties, the initial assessment of a patient with metastatic spinal disease requires a multidisciplinary team to determine the best therapy. The focus is on patient outcomes and local tumor control. ^5,7–9 Multiple specific factors are considered by the clinician to determine the best possible therapy for each patient.

Table 1.

General indications for surgery, radiosurgery & vertebral augmentation.

Surgery	Symptomatic spinal cord compression by a radiosensitive tumor (e.g. Lymphoma or myeloma)
	Mechanical instability
Radiosurgery (SRS/SBRT)	Failed prior EBRT
Vertebral augmentation	Painful pathologic fracture without significant epidural spinal cord compression
Conventional EBRT	Patients without any of the above indications
Tumor embolization	Patients with hypervascular tumors prior to surgery
Tumor ablation	Local control and immediate pain relief for focal metastatic lesion usually in conjunction with radiation or vertebral body augmentation

EBRT, external beam radiation therapy; SBRT, stereotactic beam radiation therapy; SRS, stereotactic radiosurgery.

Once the patient has been assessed from a broader perspective and systemic treatment options are considered, the next step in determining therapy is to evaluate the spinal metastasis itself. ⁷ Overall, this assessment can be done according to a decision framework to determine the optimal treatment for the patient. One commonly used framework is known as the LMNOP algorithm, ⁷ which is outlined in Table 2 and in Figure 2. First, the specific location of the tumor must be determined radiologically. When evaluating location, it’s important to determine the spinal level of the tumor, the location within the spinal column, and if multiple levels are involved. Each factor plays a role in the treatment algorithm. Next, mechanical stability is determined by using the SINS scoring system, which is outlined in Table 3. The SINS scoring system uses radiological and clinical data to determine the spinal stability and need for a surgical consult. If the spine is determined to be unstable, then the treatment is almost always to surgically stabilize the spine. ^4,7,9 Another commonly used framework is known as the NOMS framework. The NOMS framework consists of neurologic, oncologic, mechanical and systemic considerations. ²⁷ This framework also uses both the SINS grading system to assess mechanical instability and the 6-point epidural spinal cord compression scale to assess the degree of cord compression.

Table 2.

LMNOP System.

LMNOP System
L	Location	Extent of disease at symptomatic levels: Involvement of anterior &/or posterior elements
	Levels	Solitary or multiple
M	Mechanical instability	Stable (SINSa 0–6)
		Potentially unstable (SINSa 7–12)
		Unstable (SINSa 13–18)
N	Neurology	Symptomatic epidural cord compression
O	Oncology	Highly radiosensitive
		Radiosensitive
		Radioresistant
P	Patient fitness	Medical fitness for surgery
	Prognosis	Depend on tumor type (O)
	Prior therapy	Previous radiation therapy at symptomatic levels
		Failed multiple systemic treatments

^aSINS: Spinal Instability Neoplastic Score.

Figure 2.

LMNOP algorithm for spinal metastases management.

Table 3.

Components of SINS

Components of SINS
Components	SINS*
Location within the spine
Junctional (Occiput-C2, C7-T2, T11-L1 & L5-S1) Mobile (C3-C6 & L2-L4) Semi-rigid (T3-T10) Rigid (S2-S5)	3 2 1 0
Bone lesion quality
Lytic Mixed lytic/Blastic Blastic	2 1 0
Vertebral body collapse
>50% collapse <50% collapse No collapse with >50% vertebral body involved None of the above	3 2 1 0
Pain relief with recumbence & pain with movement or loading of the spine
Yes No (occasional pain not mechanical) Pain free	2 1 0
Radiographic spinal alignment
Subluxation or translation present De novo deformity (kyphosis &/or scoliosis) Normal alignment	2 1 0
Posterolateral involvement of spinal elements (facet, pedicle or costovertebral joint fracture or replacement with tumor)
Bilateral Unilateral None of the above	2 1 0

SINS, Spine Instability Neoplastic Score.

Once spinal stability is determined, the next key factor is determining the neurological risk posed by the spinal metastases. This assessment is partially based on the 'patient’s symptoms at presentation (i.e. sensory and motor deficits, myelopathy), and partially based on the potential neurological risk (i.e. degree of cord compression and the degree of epidural disease). The degree of epidural disease is commonly determined using the scoring system proposed by Bilsky et al, ^5,7 and outlined in Figure 3. The neuroradiologist plays a key role here because a disease that is only limited to bone is treated differently than the disease that is causing spinal cord compression, as the latter almost always requires immediate intervention. ^5,7,9 In some instances, spinal cord compression by an epidural tumor can be treated with low-dose conventional EBRT. These cases require the tumor to be highly radiosensitive. For this reason, among others, the next step in the algorithm is to determine the oncological assessment (i.e. tumor histology). ^5,7 Broadly, tumors are classified as radiosensitive, intermediate, or radioresistant. In general, this step will determine the type of radiation therapy that the patient receives (i.e. SBRT/SRS vs conventional EBRT). In some cases, patients with a stable spine and little to no impending neurological risk may benefit from rehabilitation interventions. These methods can reduce symptom burden and potentially prevent injury. ⁷ These interventions would clearly be less invasive and pose less risk to the patient compared to radiation therapy and surgery.

Figure 3.

Schematic representation of Bilsky's 6-point ESCC grading scale assessed on axial T ₂W image. 0: Bone only disease. 1a: Epidural extension without deformation of thecal sac. 1b: Deforamtion of thecal sac without spinal cord abutment. 1c: Deformation of thecal sac with spinal cord abutment, but no cord compression. 2: Cord compression with CSF visible around it. 3: Cord compression with no CSF around it. CSF, cerebrospinal fluid; ESCC, epidural spinal cord compression

The final step in the treatment paradigm is to determine the preferred treatment/combination of treatments based on the previously mentioned factors. The following sections will discuss each component of these management strategies in more detail with correlating radiological examples.

Role of Surgery

Surgical intervention remains an important component of the treatment algorithm for spinal metastases and metastatic spinal cord compression (MSCC). There is a huge spectrum of surgical options, ranging from minimally invasive percutaneous vertebral body augmentation to open surgical decompression, resection, and spinal column reconstruction. When tailored appropriately to the 'patient’s needs, surgery can greatly improve quality of life and prolong survival. ²⁸

The role of surgery has evolved as technology improved and morbidity decreased. Early surgical intervention involved solely decompressing the spine with a laminectomy, and had worse outcomes than radiation alone. ^29–32 This was largely due to the iatrogenic mechanical instability introduced to the spine with the laminectomy. In addition, dorsal decompression of the spine did not address the ventral epidural tumor which is the most common cause of MSCC. ¹⁵ Subsequent strategies involved posterior stabilization with screws and rods in addition to decompression and resection, with better outcomes. ^33,34 Decompressing the spinal canal allowed these patients to remain ambulatory for the remainder of their lives, while without surgery, most of these people would progress to paraplegia and its associated complications. ³⁵ Most recently, the concept of separation surgery has greatly improved outcomes when combined with radiation therapy, referred to as hybrid therapy. ^35–37

The indications for surgery include stabilization of a mechanically unstable spine, correction or prevention of spinal deformity, decompression of neural elements, tissue for histological diagnosis, removal of epidural disease to facilitate radiation and to provide local control in cases where radiation cannot be delivered. ¹⁵ In the acute setting, a new neurological deficit caused by MSCC dictates urgent decompression within 48 h. ²⁹ Given that surgical treatment cannot eradicate the disease, the goal of surgery is the preservation of neurological function and optimization of subsequent radiation. Figure 4 is a case illustration where surgery was indicated for decompression of neural elements and mechanical stabilization.

Figure 4.

62-year-old male with metastatic carcinoma lung presented with debilitated back pain. Axial T2 [A] and Sagittal T2 [B] MRI show compression fracture of the T1 vertebral body (arrowhead) with bulging of posterior cortex (arrow) and epidural soft tissue (*) surrounding the cord with distortion. VR dual energy CT image [C] the post-operative changes of T1-T2 posterolateral corpectomy with C5-T5 instrumented fusion and insertion of expandable cage. T2 axial image [D] show decompressed spinal canal post-surgery (curved arrow).

Surgical technique is dictated by the anatomic distribution of the metastatic disease. The main considerations are mechanical stability and neural compression. A commonly used metric for determining stability is the SINS, ³⁸ outlined in Table 3. High scores (13–18) are a strong indicator for an unstable spine and generally dictate spinal fusion. ³⁹ When only stabilization is needed, these procedures involve fusion of two or more levels above and below the affected vertebral level. ^37,40 Lower scores are either intermediate (7–12) or stable (0–6) and can usually be managed with less extensive surgery for stabilization or non-surgically.

Epidural compression is often measured using the Epidural Spinal Cord Compression (ESCC) scale. ⁴¹ A high degree of compression dictates the removal of the epidural component to improve the efficacy of radiation while decreasing toxicity to the spinal cord or cauda equina. ⁴² This shift towards the separation of tumor from the thecal sac rather than gross total resection of all affected structures has greatly reduced morbidity from surgical intervention. ^27,37 Rather, 360 degree evacuation of epidural disease through the transthoracic, ⁴³ retroperitoneal, ⁴⁴ or most commonly transpedicular ^45–47 is done to create space between critical structures and the tumor to be radiated. Generally, a wide laminectomy is done, followed by resection of both pedicles and posterior vertebral body. Anterior and posterior fixation is then completed. ^46,48

Minimally invasive techniques have improved outcomes in the surgical management of this disease. ^37,49 Smaller incisions and faster wound healing reduce the amount of time between surgery and radiation treatment compared to open surgery; adjuvant radiation can start as early as 1 week from surgery rather than up to 1 month. ⁷ Minimally invasive spine surgery for spinal metastasis can range from decompression alone to full 360 degree separation surgery and posterior fixation. ^47,49–51 As technology and techniques improve, the spectrum of procedures that can satisfactorily be done through a minimally invasive approach will continue to improve.

Complication rates vary widely depending on surgical technique used and range from 7 to 27%. ^43–47 The most common complications include wound breakdown and spinal fluid leak. Minimally invasive surgery generally has been shown to have lower complication rates (14%) due to smaller incisions and surgical corridors. ⁴⁹

Role of Conventional External Beam Radiation Therapy (EBRT)

Historically, EBRT has been the treatment of choice for patients with spinal metastases without bony collapse or significant neurological deficit. ⁴ The primary goal of treatment with EBRT is pain control and durable local tumor control to alleviate or prevent neurological compromise. ^4,5,7 Depending on the tumor histology, 60–70% of patients have partial or complete pain relief. 25% of patients report a complete resolution of pain, typically for a duration of 4 months. ⁷

Typically, conventional EBRT for spinal metastases confers short-term reversible toxicity. The rates of these toxicities are not consistently reported, presumably because of the mild and reversible effects. These toxicities include fatigue, transient esophagitis, mucositis, diarrhea, and general bowel irritation. ⁵² The more feared complication of EBRT is radiation myelopathy, which may take years to manifest, and is often far beyond the expected survival of typical patients undergoing conventional radiation therapy. ⁵²

EBRT can be delivered in many different doses and fractionation regimens. The most common regimens include 8 Gy in a single fraction, 20 Gy in 5 fractions, and 30 Gy in 10 fractions. The efficacy in pain control between these regimens is equivocal. ^4,5,7 Long-term efficacy has recently been shown to be more effective with the multifractionated regimens. ^5,7 Conventional EBRT has dose limitations due to the close proximity to the spinal cord. Therefore, conventional EBRT achieves the most durable long-term control when used to treat highly radiosensitive tumors. In general, radiosensitive tumors are classically considered lymphoma, myeloma, seminomas, and germinomas. ^7,9 Conversely, radioresistant tumors such sarcoma, melanoma, renal cell carcinoma, and GI malignancies are less responsive to EBRT with long-term local control rates of less than 50%. ⁷

Therefore, as outlined in the LMNOP algorithm Figure 2 conventional EBRT is a first-line therapy for radiosensitive tumors in a stable spine. Tumors that are more radioresistant are more suitable for higher doses of radiation delivered with sophisticated techniques (i.e. SRS or SBRT) that can spare the adjacent spinal cord. These techniques will be discussed in more detail in the subsequent sections.

Case illustration of EBRT for metastatic spinal disease is outlined in Figure 5. In some cases, patients initially treated with EBRT will subsequently be treated with SBRT as outlined in Figure 6.

Figure 5.

40-year-old female with metastatic left breast cancer. Initially presented with spinal metastases at T9 & T10 levels were treated with 18 Gy SBRT which was followed by new metastases lower cervical and upper thoracic region which were subsequently treated with 30 Gy 10 fractions conventional EBRT. MRI of the entire spine 11 months post-radiation treatment show heterogeneous marrow signal on pre-contrast T ₂ & T ₁W images [A, B] with patchy areas of fatty signal (arrow) and heterogeneous patchy enhancement on post-contrast T1 sagittal images [C] (arrow) representing post-treatment changes. Also note diffuse fatty marrow signal on pre-contrast sagittal T ₁W image (arrowhead) in the cervical & upper thoracic vertebrae with a small treated metastasis with marginal enhancement at T4 (curved arrow). EBRT, external beam radiation therapy; SBRT, stereotactic beam radiation therapy.

Figure 6.

71-year-old male with metastatic cholangiocarcinoma. Pre-contrast sagittal T ₁W image [A] show L2 metastasis with mild pathologic fracture (arrow). Post-EBRT pre-contrast sagittal T ₁W image [B] show further height loss (curved arrow) and new bone retropulsion severely narrowing the spinal canal (arrowhead). Remaining vertebral bodies show fatty marrow signal due to XRT (star). Post-partial corpectomy of L2 & posterior fusion from T12-L3 & pre SBRT dual energy CT myelogram volume rendered (VR) image [C] show severe compression of the thecal sac & proximity of cauda equine nerve roots (arrow) to metastatic lesion. Pre-contrast sagittal T ₁W image 1 year post-SBRT [D] show local tumor control with patchy fat marrow signal in L2 (*). Systemic progression with new metastasis at L5 (arrow). EBRT, external beam radiation therapy; SBRT, stereotactic beam radiation therapy; VR, volume rendered.

SRS/SBRT

The development of spinal SRS or SBRT has shifted the paradigm for the treatment of spinal metastasis. ⁵³ Conventional EBRT requires multiple treatments with lower doses of radiation ⁵⁴ to avoid toxicity to the spine. EBRT is also strongly affected by tumor radiosensitivity, ⁵² limiting its utility. Conversely, SRS and SBRT deliver much higher doses (12–24 Gy) in one or a few (2–5) fractions, respectively. These higher doses obviate the specificity for histology that EBRT has, and can effectively gain local control on classically radioresistant tumors. ^55–57

The most common complications relating to SRS are mild and similar to the complications found with EBRT. These include esophagitis, mucositis, dysphagia, diarrhea, paresthesia, transient laryngitis, and transient radiculitis. Radiation-induced spinal cord injury is exceedingly rare with SRS with rates as low as 0.5%. ^27,52

For example, Figures 7 and 8 are case illustrations of an effective use for SRS in a patient with metastatic renal cell carcinoma and lung carcinoma respectively; Figure 9 is a case illustration of a patient with metastatic breast cancer treated with SBRT. The downside to these treatments is that they require significantly more resources and logistical planning, ⁵⁸ as pre-operative MR imaging or CT myelogram must be done with <1 mm of motion, target delineation with a spine surgeon, and image guidance systems. ⁷ Nonetheless, the combination of separation surgery followed by SRS or SBRT, or hybrid therapy has greatly improved patient outcomes in the treatment of spinal metastasis. ³⁶

Figure 7.

60-year-old female with metastatic renal cell carcinoma to L3 and status post-SRS to this lesion received 16 Gy single fraction. Pre-SRS sagittal STIR and CT myelogram sagittal reformats [A, B] show a lytic lesion in the posterior body of L3 (arrow) with erosion of posterior cortex & epidural soft tissue (curved arrow). 3 months post-SRS pre-contrast sagittal STIR image [C] show decrease in the lesion size and resolution of epidural soft tissue (arrowhead). SRS, stereotactic radiosurgery; STIR, short tau inversion recovery.

Figure 8.

61-year-old male with NSCLC with metastasis to T3 vertebral body and bilateral posterior elements underwent separation surgery & SBRT 25 Gy in 3 fractions. Pre-operative axial T ₂W image [A] show T3 metastasis (curved arrow) with circumferential epidural and right pre-spinal soft tissue component (arrow) resulting in spinal cord compression (*). Post-operative axial T ₂W image [B] show changes of laminectomy (arrowhead) and resection of epidural soft tissue. 15 months post-SBRT sagittal & axial T ₂W image [C] show decreased tumor size and post-treatment changes (arrow). NSCLC, non-small cell lung carcinoma; SBRT, stereotactic beam radiation therapy.

Figure 9.

55-year-old female with metastatic breast cancer. Solitary L4 spinal metastasis was treated with single fraction 19 Gy SBRT. Pre-SBRT non-contrast sagittal T ₁W image [A] show hypointense sclerotic lesion along right side of L4 body (arrow). No epidural or soft tissue extension noted. Attenuation corrected FDG-PET image sagittal reformats of lower spine [B] show focal increased metabolic activity in this lesion (curved arrow). 18 months post-SBRT non-contrast sagittal T ₁W & axial T ₂W mage [C] show stable size of this sclerotic lesion (arrowhead) & FDG-PET [D] show significant decrease in metabolic activity (circle). FDG-PET, fludeoxyglucose positron emmission tomography; SBRT, stereotactic beam radiation therapy.

Percutaneous Procedures

Another category of procedures that are vital in the diagnosis and treatment of spinal metastatic disease are percutaneous interventional procedures. These include CT-guided biopsies for tumor histology, ⁵⁹ vertebral body cement augmentation and ablation, ^60–62 and pre-operative transarterial tumor embolization. ^63,64 As life expectancy increases for these patients, secondary procedures that manage long-term sequelae will become increasingly important and complement the standard treatment for spinal metastases.

One of the complications of spinal metastasis is vertebral pathologic compression fractures from compromised mechanical integrity of the bone. These fractures can cause severe pain and neurological deficit ⁶⁵ if left untreated. Vertebral body augmentation involves cement filling of the destroyed bony lesion, and is often combined with radiofrequency ablation (RFA). ⁶¹ Though there are no guidelines for minimum pain scores for ablation or vertebral body augmentation, most studies treat patients with Visual Analog Scores of 7–9. ^61,66 Ablation of tumor in the vertebral body allows for local control in patients who have already received radiation or have a contraindication to radiation. ⁶² Polymethylmethacrylate (PMMA) can then be injected to stabilize the vertebral body and has been shown to significantly improve patients' pain scores. ⁶⁷ Figure 10 is an example of a patient treated with EBRT, who subsequently required vertebral body augmentation. Radiation therapy and ablation can also be done concurrently, which allows for immediate pain resolution and improved pain scores compared to conventional radiation alone. ^60,66

Figure 10.

62-year-old female with known widely metastatic neuroendocrine tumor of lung with palliative EBRT 20 Gy in 5 fractions from C7 through T4. Post-EBRT sagittal T ₁W image [A] of the thoracic spine shows hypointense vertebral metastatic lesions (arrowhead) throughout the spine with post radiation diffuse fatty marrow changes (*). Follow-up sagittal T ₁W MR image [B] of thoracic spine show progression of metastatic disease with a new compression deformity of T7 & T9 (arrow) with loss of approximately 60% T9 body height. AP radiograph [C] show post-kyphoplasty changes at T9 (curved arrow). AP, anteroposterior; EBRT, external beam radiotherapy.

There are several different modalities for spinal ablation, including laser photocoagulation, radiofrequency ablation, cryoablation, and microwave ablation, each with unique advantages and disadvantages. While radiofrequency is the most commonly used technique, it is limited by adjacent tissue characteristics which may alter the region of treatment, and can have limited utility in posterior vertebral body lesions given their proximity to the spinal canal. ^2,66 Cryoablation has the advantage of real-time monitoring of the lesioning effect on CT or MRI, while microwave ablation is less affected by adjacent tissue characteristics. These other modalities can provide better results in certain patients, but a paucity of data has limited their widespread use to date. ⁶⁶ Complications of spinal ablation of any modality are uncommon (<15%), and include transient radiculopathy, aseptic meningitis, hematoma, and infection. ⁶⁶ Vertebral body collapse after ablation is another known complication, but can be avoided with concurrent cement augmentation. ^61,67 The most common complication of vertebral body augmentation is cement leak, which is generally asymptomatic but can cause pulmonary embolism or nerve damage in a small number of cases. ⁶⁸ The duration of pain relief varies, but is overall durable for vertebral body augmentation and RFA. For example, one study reported a significant reduction in Visual Analog Scores at 6 months post-combined augmentation and ablation. ⁶⁷ Additionally, once the maximal effects of ablation kick in, better tumor control leads to better pain control.

Pre-operative transarterial embolization can reduce the morbidity of surgery for highly vascular tumors, which can have intraoperative blood loss of 2–5 L without pre-operative embolization. ⁶⁹ Figure 11 is a case illustration of a patient with metastatic renal cell carcinoma treated with embolization prior to surgery. For tumors known to be highly vascular, a pre-operative angiogram and embolization using particles has been done to facilitate subsequent conventional therapy. However, results from the only randomized control trial to study this technique suggest that embolization may only be effective for certain hypervascular tumor types, ⁷⁰ and its effect may be clinically insignificant. Improvements in the detection of the degree of vascularity of spinal metastasis may increase this benefit. ^71–73

Figure 11.

53-year-old patient with solitary metastasis to left lateral mass of C6 underwent embolization of hypervascular renal metastatic lesion with coils and particles followed by surgical resection and posterior spinal fusion. Axial T2 MR image [A] shows hyperintense metastatic lesion involving lateral mass of C6 vertebrae (curved arrow). Multiple dark flow voids (arrow) within the lesion indicating hypervascularity. Pre-operative cervical catheter angiogram [B, C] reveals pre-embolization tumor blush on the left lateral aspect (circle) and post-embolization angiogram shows decreased tumor blush, coils and plugs (circle).

Summary

Advancements in technology and multidisciplinary management have revolutionized the treatment of spinal metastases. It is important for the radiologist to be familiar with these advancements and to understand the relevant imaging findings that determine the best treatment for the patient and tailor the reports accordingly to convey needed information. The 'patient’s quality of life can be improved by utilizing minimally invasive interventions. A multidisciplinary management system represents the best option for the treatment of spinal metastatic disease based on the current evidence. Cases that once required aggressive surgical resection or low-dose conventional EBRT can now be managed with separation surgery or spine SRS/SBRT. These methods have been proven to decrease patient morbidity, improve local tumor control, and provide more durable and longer lasting pain control. Depending on the 'patient’s clinical scenario, some cases might be optimally managed with interventional procedures, rehabilitation, or palliative care. Overall, special attention to the relevant details of metastatic spinal disease at initial imaging will translate into improved patient outcomes.