Imaging of Sacral Masses: Self-Assessment Module

Transcription

1 1.5 CME AJR Integrative Imaging LIFELONG LEARNING FOR RADIOLOGY Imaging of Sacral Masses: Self-Assessment Module Alice S. Ha 1, Felix S. Chew ABSTRACT The educational objectives for this self-assessment module are for the participant to exercise, self-assess, and improve his or her understanding of sacral masses and the key imaging characteristics of various sacral masses. INTRODUCTION This self-assessment module on sacral masses has an educational component and a self-assessment component. The educational component consists of four required articles that the participant should read. The self-assessment component consists of nine multiple-choice questions with solutions. All of these materials are available on the ARRS Website (www. arrs.org). To claim CME and SAM credit, each participant must enter his or her responses to the questions online. EDUCATIONAL OBJECTIVES By completing this educational activity, the participant will exercise, self-assess, and improve his or her understanding of: A. The imaging evaluation of sacral masses. B. The radiologic features of different sacral tumors. REQUIRED READING 1. Venkatanarasimha N, Brown S, Suresh P. AJR teaching file: coccydynia with midline sacral mass. AJR 2010; 195[suppl 3]:S29 S31 2. Llauger J, Palmer J, Amores S, Bagué S, Camins A. Primary tumors of the sacrum: diagnostic imaging. AJR 2000; 174: Diel J, Ortiz O, Losada RA, Price DB, Hayt MW, Katz DS. The sacrum: pathologic spectrum, multimodality imaging, and subspecialty approach. RadioGraphics 2001; 21: Disler DG, Miklic D. Imaging findings in tumors of the sacrum. AJR 1999; 173: RECOMMENDED READING 1. Gerber S, Ollivier L, Leclère J, et al. Imaging of sacral tumours. Skeletal Radiol 2008; 37: Murphey MD, Andrews CL, Flemming DJ, Temple HT, Smith WS, Smirniotopoulos JG. From the archives of the AFIP: primary tumors of the spine radiologic pathologic correlation. RadioGraphics 1996; 16: INSTRUCTIONS 1. Complete the educational and self-assessment components included in this issue. 2. Visit and log in. 3. Select Self-Assessment Modules from the Lifelong Learning box in the lower left of the page. 4. Add the SAM to your shopping cart and order the online SAM as directed. (The SAM, including questions, must be ordered to be accessed even though the activity is free to ARRS members.) After purchasing the SAM, click on OK; you will be returned to the ARRS home page. 5. Click on the My Education tab at the top of the page, then on My Online Products. (Note: You must be logged in to access this personalized page.) 6. You can also access the purchased SAM by logging on to 7. Answer the questions online to obtain SAM credit. Keywords: bone tumor, CT, MRI, sacrum DOI: /AJR Received December 22, 2009, 2009; accepted after revision May 2, Both authors: Department of Radiology, University of Washington, Box , 4245 Roosevelt Way NE, Seattle, WA Address correspondence to A. S. Ha (aha1@uw.edu). AJR 2010; 195:S32 S X/10/1953 S32 American Roentgen Ray Society S32 AJR:195, September 2010

2 Sacral Masses QUESTION 1 Which of the following sacral tumors is most common? A. Giant cell tumor (GCT). B. Ependymoma. C. Chordoma. D. Ewing sarcoma. QUESTION 2 All of the following factors may contribute to delayed diagnosis of sacral mass EXCEPT: A. The sacrum can accommodate a large mass before symptoms arise. B. Patients present with nonspecific symptoms such as back pain. C. The sacrum is the site of early red marrow conversion. D. Radiography has low sensitivity for sacral masses. QUESTION 3 Among the following, which is the most common site for chordomas? A. Skull base. B. Thoracic spine. C. Thoracolumbar junction. D. Sacrum. QUESTION 4 How are sacral chondrosarcomas and sacral chordomas similar? A. Both are eccentric in position. B. Both have internal calcifications. C. Both have internal areas of high T1 signal. D. Both may arise from osteochondromas. QUESTION 5 Giant cell tumor (GCT) of the sacrum can possess any of the following characteristics EXCEPT: A. Local aggressiveness. B. Homogeneously low T2 signal on MRI. Solution to Question 1 The sacrum, the site of hematopoietic marrow in adults, is a common site for metastatic disease as well as hematologic malignancies such as multiple myeloma and lymphoma. Metastasis is the most common tumor involving the sacrum [1]. Metastases from lung, breast, kidney, prostate, head and neck, gastrointestinal tract, and skin cancers are most common in the sacrum. Most metastases are lytic, although some are blastic (i.e., breast and prostate cancers). Multiple myelomatous lesions are scattered multiple lytic lesions without sclerotic borders. C. Hypervascularity. D. Varied T2 signal on MRI. QUESTION 6 How are sacral aneurysmal bone cysts and sacral GCTs similar? A. Both are centered in anterior spinal elements. B. Both are hypervascular. C. Both contain multiple fluid fluid levels. D. Both stay within the sacrum and do not cross joint spaces. QUESTION 7 In images of primary sacral lymphoma, all of the following are possible appearances EXCEPT: A. Normal on conventional radiographs. B. Central sclerotic nidus on CT. C. Hot on bone scans. D. Large soft-tissue mass on MRI. QUESTION 8 All of the following statements are true about Tarlov cysts (i.e., sacral meningeal cysts) EXCEPT: A. They are extradural. B. They can erode and remodel adjacent bone. C. They contain a sacral nerve root. D. They are associated with partial sacral agenesis. QUESTION 9 Other than metastases, what is the most common type of malignant intramedullary spinal tumor of the sacrum in adults? A. Myxopapillary ependymoma. B. Chordoma. C. Chondrosarcoma. D. Malignant peripheral nerve sheath tumor. Primary benign and malignant tumors of the sacrum account for 7% of all intraspinal tumors [2]. Aside from lymphoproliferative tumors, chordoma is the most common primary malignant tumor of the sacrum (20 34%) with a 2:1 male-to-female predominance. Option C is the best response. Chordoma is most often found in middle-aged patients (age range, years), with peak incidence in the fifth decade. According to the Mayo Clinic series [3], 6% of malignant bone tumors involve the sacrum, with 50% consisting of chordomas. Ewing sarcoma (option D) is not the best re- AJR:195, September 2010 S33

3 Ha and Chew sponse because it accounts for about 8% of sacral bone tumors, mostly in children. Ependymoma is an intramedullary spinal tumor of the sacrum that is relatively rare in occurrence. Option B is not the best response. Giant cell tumors of the spine, representing only 3 7% of all giant cell tumors are uncommon. Therefore, option A is not the best response. Solution to Question 2 Because of the sacrum s curved shape and overlapping pelvic organs, masses in the sacrum are poorly visualized on radiography [4]. Axial imaging with CT or MRI is often used to detect and further characterize sacral masses. Although some characteristics help to limit the differential diagnosis, imaging-guided biopsy is often required to establish a specific diagnosis. Sacral masses are often large at diagnosis because the sacrum can accommodate a large mass before the mass impinges on an exiting nerve or adjacent intrapelvic organ. Often, patients with sacral masses complain of vague pelvic pain, back pain, leg pain, or incontinence [2, 5]. So, options A, B, and D are true and thus not the best responses, whereas the sacrum being site of hematopoietic marrow in adults is not a reason for delayed diagnosis. Option C is the best response. Solution to Question 3 Development of the human spine starts during embryogenesis and continues into the third decade of life. The notochord is involved in gastrulation and formation of the neural plate. The notochord eventually gives rise to the nucleus pulposus of the adult spine. Nonneoplastic notochordal vestiges are seen in up to 2% of cadavers, most frequently in the midline near the sphenooccipital synchondrosis and in the sacrococcygeal regions. The distribution of chordomas parallels this distribution because chordomas are thought to arise from malignant degeneration of notochordal remnants [5, 6]. Chordoma involves the sacrococcygeal region in 50 60% of the cases, so option D is the best response [7]. Chordoma involves the skull base (i.e., clivus or sphenooccipital region) in 30 35% of cases, so options A, B, and C are not the best responses. The sacrococcygeal form of chordoma has a higher level of metastases (i.e., lung, skin, and bone) than the skull base forms, most likely because of the longer survival time of patients with the sacrococcygeal form. Although considered a low-grade tumor, chordoma is difficult to treat. Prognosis is defined by its propensity to recur. Fuchs et al. [5] recently noted a 5-year survival of 74% and a 10-year survival rate of 52% and concluded that the single most important predictor of survival and recurrence was the margin achieved during surgical resection. All patients with a wide margin of resection survived. Adjuvant radiation therapy increases disease-free intervals, but chordoma is insensitive to chemotherapy [3 6]. Solution to Question 4 Chondrosarcomas account for 7 12% of malignant primary tumors of the spine [2]. Within the spine, chondrosarcoma is most common in the thoracic spine and is rare in the sacrum. Chondrosarcomas are usually eccentric in location, whereas chordomas are midline because chordomas are derived from the notochordal remnants. Option A is false and thus not the best response. Found in older patients (average age, 45 years), chondrosarcomas usually show high T2 signal but may show heterogeneous T2 signal because of the presence of a mineralized and unmineralized chondroid matrix. Therefore, both chondrosarcoma and chordomas can have intralesional calcifications, making option B the best response. There is usually no internal hemorrhage, hence allowing it to be distinguished from chordomas; therefore, chondrosarcomas do not have high T1 signal, making option C false and thus not the best response. Chordomas, on the other hand, may show areas of high T1 signal due to focal hemorrhage or mucoid content. There is often septal enhancement with gadolinium [5]. Chondrosarcomas may arise de novo or secondarily from osteochondromas. Option D is false and thus not the best response. Solution to Question 5 Giant cell tumor (GCT) of the spine represents only 7% of all GCTs; however, most of those occur in the sacrum. GCTs represent the second most common primary sacral neoplasm after chordoma and are seen most commonly in patients ranging from 15 to 40 years old with a female predominance [8]. GCTs are lytic, expansile, and destructive lesions that often involve the upper sacrum and are eccentric in position. They can extend across the sacroiliac joint and disk space to mimic infection unlike appendicular GCTs, which never cross joints [5]. GCTs consist of osteoclastic giant cells within a spindle cell stroma. On CT, they are vascular soft-tissue masses with a thin sclerotic rim; they may require embolization before surgery. Therefore, option C is not the best response. On MRI, GCTs are heterogeneous on T1 due to areas of hemorrhage. They are heterogeneous on T2 due to focal areas of necrosis, hemorrhage, and fibrosis, so option D is not the best response. From 5% to 10% of GCTs are malignant and can metastasize. Option B is false and therefore the best response. Although GCTs are benign tumors, prognosis is not favorable because of their locally aggressive nature (option A is not the best response), the subsequent difficulty in completely excising them, and a high recurrence rate of 40 60% [3, 7]. S34 AJR:195, September 2010

4 Sacral Masses Solution to Question 6 Aneurysmal bone cysts (ABCs) have a 4% incidence in the sacrum [9]. Twenty percent of ABCs are in the spine most commonly in the thoracic spine and rarely in the sacrum. Unlike GCTs, which are found in anterior spinal elements, ABCs are often centered in the posterior elements of the spine. Option A is false and thus not the best response. More than 80% of ABCs are detected by the age of 20 years with a slight female predominance, whereas GCTs are most common in patients between 15 and 40 years old. ABCs are characterized by multiple septated compartments containing fluid fluid levels often containing hemorrhagic debris. ABCs are not true neoplasms but are thought to be reactive lesions from localized disturbances of osseous blood flow, possibly because of a prior trauma or other adjacent bony neoplasms (both benign or malignant) [2]. Only a subset of GCTs contain components of ABC and hence contain fluid fluid levels. Option C is false and thus not the best response. ABCs can be hypervascular; thus, option B is the best response. ABCs can cross disk spaces to involve adjacent vertebral bodies, mimicking infection; this feature is also seen in chordomas and GCTs. Option D is false and thus not the best response. Usually, ABCs do not contain a softtissue component except for solid-variant ABCs [10]. Solution to Question 7 Primary lymphoma of the sacrum has a peak incidence during the second and third decades and is rare in children younger than 10 years old. There is a 2:1 male predominance [9]. There is intense radiotracer uptake on bone scan. When visible on radiographs, lymphoma is a permeative lytic lesion. Bone marrow invasion can be massive on MRI despite normal findings on radiographs. Often, there is a large soft-tissue mass with no visible cortical defects [1]. Options A, C, and D are true and thus not the best responses. A central sclerotic nidus is a key characteristic of osteoid osteoma not of primary lymphoma. Option B is false and therefore the best response. Solution to Question 8 A Tarlov cyst is a focal extradural dilatation of the sacral nerve root sheath, also known as a sacral meningeal cyst and perineural cyst. Tarlov cysts contain sacral root nerve fibers. Because of CSF pulsations, they can erode and remodel the sacral canal or sacral neural foramina [5]. Options A, B, and C are true and thus not the best responses. Tarlov cysts are usually asymptomatic, but large cysts can cause neurologic symptoms. They are common; they were seen in 5% of 500 consecutive MRIs of the lumbosacral spine of which five of 23 patients with cysts had symptoms [11]. Symptomatic lesions can be treated with aspiration and percutaneous fibrin glue injection therapy [12]. Anterior meningoceles, not Tarlov cysts, are associated with partial sacral agenesis. Option D is false and therefore the best response. Solution to Question 9 A minority of sacral tumors arise within the sacral spinal canal. Benign tumors such as schwannomas and neurofibromas are rare in the sacrum [1]. Malignant degeneration of these tumors are even more rare, making option D false. Ependymomas are the most common malignant sacral tumor within the spinal canal. Option A is the best response. The intramedullary type of ependymoma can occur anywhere but occurs most often in the cervical spine, whereas the myxopapillary type occurs exclusively in the conus medullaris and filum terminale. Myxopapillary ependymomas arise from the ependymal glia of the filum terminale and are therefore intradural; extradural forms are very rare. Myxopapillary ependymoma has a mean age of occurrence of 36 years and a slight male predominance. Myxopapillary ependymoma is a benign tumor with World Health Organization histologic grade I. It can cause local bony destruction but rarely metastasizes, with rare exceptions for the very rare extradural forms. Ependymomas are vascular soft-tissue masses with areas of hemorrhage and mucinous degeneration. On CT, they can cause sacral neural foramina widening and adjacent bone destruction. On MRI, they show high T2 signal with avid contrast enhancement. Drop metastases from other CNS tumors such as primary neuroectodermal tumor and choroid plexus tumor can settle in dependent portions of the sacral spinal canal. Although large chondrosarcomas and chordomas can extend into the neural foramina, these tumors are not intramedullary in origin; options B and C are false [1, 13]. References 1. Gerber S, Ollivier L, Leclère J, et al. Imaging of sacral tumours. Skeletal Radiol 2008; 37: Murphey MD, Andrews CL, Flemming DJ, Temple HT, Smith WS, Smirniotopoulos JG. From the archives of the AFIP: primary tumors of the spine radiologic pathologic correlation. RadioGraphics: 1996; 16: Unni KK. Dahlin s bone tumors: general aspects and data on 11,087 cases, 5th ed. Philadelphia, PA: Lippincott-Raven, Diel J, Ortiz O, Losada RA, Price DB, Hayt MW, Katz DS. The sacrum: pathologic spectrum, multimodality imaging, and subspecialty approach. Radio- Graphics 2001; 21: Fuchs B, Dickey ID, Yaszemski MJ, Inwards CY, Sim FH. Operative management of sacral chordoma. J Bone Joint Surg Am 2005; 87: Venkatanarasimha N, Brown S, Suresh P. AJR teaching file: coccydynia with midline sacral mass. AJR 2010; 195[suppl 3]:S29 S31 7. Farsad K, Kattapuram SV, Sacknoff R, Ono J, Nielsen GP. Sacral chordoma. AJR:195, September 2010 S35

5 Ha and Chew RadioGraphics 2009; 29: Llauger J, Palmer J, Amores S, Bagué S, Camins A. Primary tumors of the sacrum: diagnostic imaging. AJR 2000; 174: Disler DG, Miklic D. Imaging findings in tumors of the sacrum. AJR 1999; 173: Vester H, Wegener B, Weiler C, Baur-Melnyk A, Jansson V, Dürr H. First report of a solid variant of aneurysmal bone cyst in the os sacrum. Skeletal Radiol 2010; 39:73 77 FOR YOUR INFORMATION 11. Paulsen RD, Call GA, Murtagh FR. Prevalence and percutaneous drainage of cysts of the sacral nerve root sheath (Tarlov cysts). AJNR 1994; 15: ; discussion, Patel MR, Louie W, Rachlin J. Percutaneous fibrin glue therapy of meningeal cysts of the sacral spine. AJR 1997; 168: Shors SM, Jones TA, Jhaveri MD, Huckman MS. Best cases from the AFIP: myxopapillary ependymoma of the sacrum. RadioGraphics 2006; 26[suppl 1]:S111 S116 The reader s attention is directed to the AJR Teaching File on which this SAM is based, which begins on page S29. S36 AJR:195, September 2010