PM R 10 (2018) 880-885
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Neural Foraminal Lesions: An Imaging Overview Raza Mushtaq, MD, Jack Porrino, MD, Sylvestor A. Moses, PhD, ´n Pe ´rez-Carrillo, MD, MSc Gloria J. Guzma Introduction and Anatomic Considerations The neural foramina allow passage of spinal nerves, arteries, veins, and lymphatics from the spinal canal to the periphery [1,2] and are formed by various surrounding osseous and nonosseous structures. The anterior border is made up of the posterior aspect of adjacent vertebral bodies, the intervertebral disk, and the posterior longitudinal ligament. The superior and inferior borders of the foramen are formed by the vertebral notches of the superior and inferior vertebral pedicles. The facet, or zygapophyseal, joints form the posterior border [1,2]. Laterally, the foramen is covered by overlying psoas muscle and fascia [2]. Clinical Background Many lesions have been associated with nerves exiting at the level of the neural foramen. The purpose of this review is to describe the various pathologies at this site, which typically present with compression through the neural foramina in a longitudinal fusiform manner [3]. Peripheral nerve sheath tumors (PNSTs) constitute the majority of these lesions; however, there are a large number of foraminal/extraforaminal and neoplastic/non-neoplastic differential considerations for such lesions [3,4]. Neoplastic Lesions Benign PNSTs Neurofibromas and schwannomas (neurilemomas) are the 2 major benign PNSTs [2,5,6]. Peripheral nerves can be involved at any level but typically afflict major nerve trunks [5]. Neurofibromas Neurofibromas constitute 5% of all benign soft-tissue neoplasms. These tumors typically affect young patients in their second or third decades of life, without a
sex predilection [6,7]. These are usually solitary lesions involving superficial small cutaneous nerves that present as small, painless masses. Neurofibromas can also affect deeper, larger major nerve trunks, which often produce neurologic symptoms [5]. On histology, these lesions are composed of abundant collagen with interlacing fascicles of elongated cells [6]. Nearly 10% of neurofibromas are associated with neurofibromatosis. These patients have a greater incidence of malignant transformation [5]. In neurofibromatosis type 1 (NF1), neurofibromas have been divided as localized, plexiform, and diffuse types on a pathologic basis. The localized neurofibromas in NF1 tend to be larger and multiple, involving the deeper nerves. Plexiform neurofibromas involve longer segments of major nerves, resulting in large multilobulated masses that are considered pathognomonic for NF1. Diffuse neurofibromas occur most commonly in children and are often localized within the subcutaneous tissues [5]. Cross-sectional evaluation of neurofibromas on computed tomography (CT) reveals a well-defined low attenuating mass, often intradural extramedullary, that demonstrates homogeneous enhancement with associated pressure related dysplastic osseous abnormalities [3,8] (Figure 1). On magnetic resonance imaging (MRI), these lesions demonstrate hypointense signal on T1-weighted sequences and hyperintense signal on T2-weighted sequences with avid enhancement on postcontrast images [3,5,6]. A characteristic target sign has been described on T2-weighted sequences with a central hypointense region surrounded by homogeneously hyperintense signal (Figure 1) [3]. The central hypointense signal is due to high content of dense fibrous and collagenous material, whereas the peripheral hyperintense signal is constituted predominately by abundant myxoid material with high fluid content. A similar target sign can be appreciated on sonographic examination, with a well-defined hypoechoic lesion containing a central hyperechoic region [5].
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Figure 1. Plexiform neurofibroma in a patient with neurofibromatosis type 1. There is an enlarged left neural foramen (asterisk) on the axial computed tomographic (CT) image (A) related to an expansile mass (outlined) seen best on the corresponding axial T2-weighted magnetic resonance image (MRI) (B). Several target signs (arrows)da central hypointense region surrounded by homogeneously hyperintense T2 signaldare denoted on MRI. Hardware about the cervical spine is incidentally noted on the CT image.
Schwannomas Small schwannomas are generally asymptomatic, with larger masses causing symptoms from compression of adjacent nerves [5]. Histologically, schwannomas are composed of varying degrees of Antoni A (organized areas of cellular spindle cells) and Antoni B (loosely arranged areas of hypocellular myxoid tissue) regions that are often S-100 proteinepositive on immunohistochemical analysis [6,9]. Imaging characteristics of schwannomas are similar to those of neurofibromas, which typically present as solitary, lobulated, and grossly encapsulated intradural extramedullary masses. However, schwannomas tend to demonstrate cystic degeneration, hemorrhage, and xanthomatous changes (Figure 2) [3,5]. In addition, an eccentric location of the mass compared with the
associated nerve suggests a histologic diagnosis of schwannoma, whereas a central location favors neurofibroma [3]. Schwannomas often allow for nerve-sparing surgeries due to their encapsulated nature; conversely, neurofibromas require sacrificing the involved nerve due to their intimate relationship with the nerve [5]. Malignant Peripheral Nerve Sheath Tumors Malignant peripheral nerve sheath tumors (MPNSTs) are also known as malignant schwannomas, neurogenic sarcomas, and neurofibrosarcomas. MPNSTs affect a slightly older population, those 20-50 years of age, as compared with benign PNSTs. Nearly 50% of MPNSTs are found in patients with NF1, but only 5% of patients with NF1 develop MPNSTs [5].
Figure 2. Cervical schwannoma. Axial (A) and coronal (B) fat-suppressed postcontrast T1-weighted magnetic resonance images demonstrate an avidly enhancing mass expanding the right C2-C3 neural foramen and causing lateral displacement and severe compression of the spinal cord from the C2 through C4 level (the mass is outlined in [A] and denoted by closed arrows in [B]). Vb, vertebral body; the open arrow in (A) points to the normal left neural foramen.
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These tumors tend to be large, fusiform masses often presenting with extensive central necrosis and hemorrhage, affecting major nerve trunks, which results in pain and neurologic symptoms [5]. Differentiation of malignant from benign PNSTs is often difficult on imaging. Larger size (>5 cm) and ill-defined margins raise suspicion for malignant nature of the neoplasm [5,7]. Calcification within the mass is more commonly seen in malignant lesions (Figure 3) [5]. The MPNST demonstrates increased uptake on 18-fluorodeoxyglucose positron emission tomography, but 18-fluorodeoxyglucose positron emission tomography cannot reliably differentiate low-grade malignant PNSTs from benign plexiform neurofibromas. 18F-thymidine has been studied as a biomarker to further delineate low-grade MPNSTs from benign plexiform neurofibromas [10,11]. Chordoma Chordomas are a rare differential consideration for a neural foraminal mass, arising from ectopic remnants of the embryonic notochord [3,12]. Nearly 50% of chordomas are located in the sacrococcygeal region, 35% in the spheno-occipital clival synchondrosis, and the remaining within spinal vertebrae [12]. A few case reports have described neural foramen extension of chordomas presenting with compression through the neural foramina in a longitudinal fusiform manner [13]. These are slow-growing tumors; however, they are locally aggressive, often resulting in osseous and softtissue destruction. Histologically, they demonstrate abundant intracellular mucin matrix production with the presence of large vacuolated physaliphorous cells [12-14]. On imaging, these lesions are often centered in the midline position and demonstrate calcifications and destruction of adjacent vertebrae and intervertebral disks (Figure 4). The preoperative role of imaging in these cases is to define the extent of disease and isolate potential areas of surgical complications [15].
Figure 3. Malignant peripheral nerve sheath tumor in a man with neurofibromatosis type 1. A large, enhancing malignant peripheral nerve sheath tumor is present (arrows) arising from the left S1 nerve root (asterisk) on the axial T1-weighted fat suppressed postcontrast magnetic resonance image.
Solitary Bone Plasmacytoma Solitary bone plasmacytoma is a rare, solitary plasma cell bone or soft-tissue tumor constituting only 3%-5% of all monoclonal gammopathies [16]. Some consider these lesions to represent early stages of multiple myeloma and are differentiated on histology by their lack of myelomatous cells [3,16]. These lesions typically affect vertebral bodies due to high red marrow content and extend to involve the posterior elements, including pedicles, and when large enough, they can extend through a neural foramen [3,17]. The majority of these lesions have nonspecific imaging characteristics [3]. In few cases, a classic “minibrain” appearancedexpansile lesion within a vertebral bodydon axial images has been described and is considered pathognomonic for solitary plasmacytoma [3,17]. The appearance is thought to represent compensatory thickening of cortical struts from stress due to the underlying lytic process [17]. In a small series of 6 patients, the authors described imaging characteristics as predominantly hypointense on T1-weighted sequences and heterogeneously hyperintense on T2weighted sequences. They also reported low signal curvilinear areas within vertebral lesions or cortical irregularity in 4 of the 6 patients [16]. Spine Metastases Approximately 90% of spinal masses found on imaging are from metastases. Although most comprise bone metastases, a small subset may present with spinal canal invasion and cord compression. The most common region of the spine affected is the thoracic, followed by the lumbar and cervical spine. The posterior vertebral body is the most common initial site of metastasis, with lesions rarely involving the intradural and intramedullary regions [18]. The most common primary sites of bone metastases include breast, lung, and prostate. Cancer cells access the spine through a variety of routes, including the arterial system, the Batson venous plexus, cerebrospinal fluid (CSF), and through direct invasion from paraspinous tumors [18]. Once in the bone marrow, breast and lung tumor cell-produced factors, such as parathyroid hormoneerelated peptide, interfere with normal osteoclast and osteoblast homeostasis through dysregulation of the receptor activator of nuclear factor-kB ligand and osteoprotegerin pathways, thus resulting in osteolytic lesions [19]. The osteoblastic nature of prostate bone metastases is not well known but is thought to involve fibroblastic growth factors and endothelin-1, which have been found to stimulate bone formation in vivo [19]. Although radiographs remain the first-line imaging modality for bone metastasis investigation, CT is superior in the detection of trabecular and cortical bone
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Figure 4. Chordoma. Axial fat suppressed postcontrast T1-weighted magnetic resonance image (A) demonstrates a heterogeneously enhancing right neural foraminal mass (outlined) extending into the epidural space resulting in severe central canal stenosis and cord compression (the cord is denoted by an asterisk). Sagittal T2-weighted magnetic resonance image (B) demonstrates the irregular lobulated T2 hyperintense mass (arrows) within the superior cervical spine involving the vertebral bodies of C1-C3 and their posterior elements. Vb, vertebral body; the open arrow in (A) points to the normal left neural foramen.
destruction and soft-tissue extension [20]. MRI is useful in determining soft-tissue involvement, especially for delineating spinal cord compression and visualizing distortions of CSF spaces. MRI of the whole spine is the gold-standard for the evaluation of spinal metastases [21]. Non-Neoplastic Lesions Aneurysmal Bone Cyst Aneurysmal bone cyst (ABC) is a non-neoplastic cystic lesion of the bone. It is characteristically described as a
highly vascular, hemorrhagic tumor consisting of blood lacunae separated by connective septa that contain a mixture of giant cells, osteoblasts, and reactive woven bone [22]. Although previously thought to be of unknown origin, it is now classified as a true benign primary tumor with most ABCs having a translocation resulting in the activation of gene USP6 on chromosome 17p13 [23]. Although ABCs can occur in any bone, spinal involvement is seen in 20% of cases [24]. ABCs typically arise in the posterior vertebral elements and may invade the pedicles and vertebral bodies. ABCs can be locally aggressive and can present with
Figure 5. Large multilocular aneurysmal bone cyst throughout the lumbar spine. Axial soft-tissue algorithm computed tomographic (A) and T2weighted magnetic resonance imaging (MRI) (B) images demonstrate a multilocular cystic mass (arrows) protruding through and enlarging the neural foramina. The mass causes remodeling of the L2 through S3 vertebral bodies and the posterior elements, and exhibits dependent fluid levels, as seen on the sagittal T2-weighted MRI (C). Vb, vertebral body.
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Figure 6. Intraforaminal synovial cyst. Axial T2-weighted (A) and sagittal T2 fat-suppressed (B) magnetic resonance images demonstrate a hyperintense lesion (closed arrows) within the left L5-S1 foramen and lateral recess resulting in compression of the L5 nerve root. There is degenerative bone marrow and soft-tissue edema (open arrows) involving the left L5 facet joint.
significant neurologic and structural impairment of the spine [25]. ABCs typically present as an expansile radiolucent lesion with cortical destruction on plain radiographs. CT imaging of ABCs reveals characteristic multiple fluid levels [26]. MRI is helpful in further defining the internal characteristics, including the thin membranous septa and fluid levels [22]. However, definitive diagnosis of ABC requires biopsy and histologic examination (Figure 5).
Intraforaminal Synovial Cyst Intraforaminal synovial cysts fall under the category of lumbar synovial cysts and typically form from the zygapophyseal joint capsule of the lumbar spine. These generally occur in the context of degenerated facet joints and thus are also referred to as juxta-articular or juxtafacet cysts (JFCs). The etiology of these synovial and ganglion cysts is relatively unknown but is thought to be due to postsurgical changes or repetitive microtrauma [27,28]. As such, JFCs are almost always seen in the older population and very rarely seen in adolescence and young adulthood. Most JFCs are located at the L4-L5 level, which typically bears the greatest amount of movement within the lumbar spine [29]. Intraforaminal synovial cysts are relatively rare and clinically present with low back pain and lumbar radiculopathy. As such, differential considerations are broad and include disk herniation, neoplastic lesion, cystic nerve root tumor, tortuous vertebral artery, extradural arachnoid cyst, and traumatic pseudomeningocele [3,30].
Imaging characterization of lumbar synovial cysts is achieved by CT and MRI (Figure 6). The fluid of the cystic lesion is similar to the CSF. However, the presence of hemorrhage, necrosis, or calcifications may cause the cyst to develop radiographic characteristics seen in the aforementioned differential. CT and CT myelogram may show hypodense-to-isodense cystic centers with hyperdense rims reflecting calcification of the capsule [31]. MRI is the preferred choice for diagnosing JFCs, with a reported greater diagnostic accuracy and increased sensitivity when compared to CT [32]. MRI typically reveals low-intensity signal on T1-weighted images and a high-intensity signal on T2-weighted sequences [33,34]. Even though both synovial and ganglion cysts may present with similar clinical and radiographic features and can only be distinguished by histologic methods, the treatment and prognosis of either type of cyst is the same [29]. References 1. Yousem D, Grossman R. Neuroradiology: The Requisites. Philadelphia, PA: Elsevier Health Sciences; 2010. 2. Gilchrist RV, Slipman CW, Bhagia SM. Anatomy of the intervertebral foramen. Pain Physician 2002;5:372-378. 3. Kivrak AS, Koc O, Emlik D, Kiresi D, Odev K, Kalkan E. Differential diagnosis of dumbbell lesions associated with spinal neural foraminal widening: Imaging features. Eur J Radiol 2009;71:29-41. 4. Zibis AH, Markonis A, Karantanas AH. Unusual causes of spinal foraminal widening. Eur Radiol 2000;10:144-148. 5. Lin J, Martel W. Cross-sectional imaging of peripheral nerve sheath tumors: Characteristic signs on CT, MR imaging, and sonography. AJR Am J Roentgenol 2001;176:75-82. 6. Murphey MD, Smith WS, Smith SE, Kransdorf MJ, Temple HT. From the archives of the AFIP. Imaging of musculoskeletal neurogenic
R. Mushtaq et al. / PM R 10 (2018) 880-885
7.
8.
9.
10.
11.
12.
13. 14.
15. 16. 17.
18. 19. 20.
tumors: Radiologic-pathologic correlation. Radiographics 1999;19: 1253-1280. Stull MA, Moser RP, Kransdorf MJ, Bogumill GP, Nelson MC. Magnetic resonance appearance of peripheral nerve sheath tumors. Skeletal Radiol 1991;20:9-14. Restrepo CS, Riascos RF, Hatta AA, Rojas R. Neurofibromatosis type 1: Spinal manifestations of a systemic disease. J Comput Assist Tomogr 2005;29:532-539. Kakkar C, Shetty CM, Koteshwara P, Bajpai S. Telltale signs of peripheral neurogenic tumors on magnetic resonance imaging. Indian J Radiol Imaging 2015;25:453-458. Ferner RE, Gutmann DH. International consensus statement on malignant peripheral nerve sheath tumors in neurofibromatosis. Cancer Res 2002;62:1573-1577. Ferner RE, Lucas JD, O’Doherty MJ, et al. Evaluation of (18)fluorodeoxyglucose positron emission tomography ((18)FDG PET) in the detection of malignant peripheral nerve sheath tumours arising from within plexiform neurofibromas in neurofibromatosis 1. J Neurol Neurosurg Psychiatry 2000;68:353-357. Mortele ´ B, Lemmerling M, Mortele ´ K, et al. Cervical chordoma with vertebral artery encasement mimicking neurofibroma: MRI findings. Eur Radiol 2000;10:967-969. Karakida O, Aoki J, Seo GS, et al. Epidural dumbbell-shaped chordoma mimicking a neurinoma. Pediatr Radiol 1996;26:62-64. Wang AM, Joachim CL, Shillito J, Morris JH, Zamani AA, Rumbaugh CL. Cervical chordoma presenting with intervertebral foramen enlargement mimicking neurofibroma: CT findings. J Comput Assist Tomogr 1984;8:529-532. Murphy JM, Wallis F, Toland J, Toner M, Wilson GF. CT and MRI appearances of a thoracic chordoma. Eur Radiol 1998;8:1677-1679. Shah BK, Saifuddin A, Price GJ. Magnetic resonance imaging of spinal plasmacytoma. Clin Radiol 2000;55:439-445. Major NM, Helms CA, Richardson WJ. The “mini brain”: Plasmacytoma in a vertebral body on MR imaging. AJR Am J Roentgenol 2000;175:261-263. Harel R, Angelov L. Spine metastases: Current treatments and future directions. Eur J Cancer Oxf Engl 1990;2010(46):2696-2707. Roodman GD. Mechanisms of bone metastasis. Discov Med 2004;4: 144-148. Snyder BD, Cordio MA, Nazarian A, et al. Noninvasive prediction of fracture risk in patients with metastatic cancer to the spine. Clin Cancer Res 2009;15:7676-7683.
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21. Loughrey GJ, Collins CD, Todd SM, Brown NM, Johnson RJ. Magnetic resonance imaging in the management of suspected spinal canal disease in patients with known malignancy. Clin Radiol 2000; 55:849-855. 22. Rapp TB, Ward JP, Alaia MJ. Aneurysmal bone cyst. J Am Acad Orthop Surg 2012;20:233-241. 23. Mascard E, Gomez-Brouchet A, Lambot K. Bone cysts: Unicameral and aneurysmal bone cyst. Orthop Traumatol Surg Res 2015; 101(1 Suppl):S119-S127. 24. Chan MSM, Wong Y-C, Yuen M-K, Lam D. Spinal aneurysmal bone cyst causing acute cord compression without vertebral collapse: CT and MRI findings. Pediatr Radiol 2002;32:601-604. 25. Boriani S, De Iure F, Campanacci L, et al. Aneurysmal bone cyst of the mobile spine: Report on 41 cases. Spine 2001;26:27-35. 26. Hecht AC, Gebhardt MC. Diagnosis and treatment of unicameral and aneurysmal bone cysts in children. Curr Opin Pediatr 1998;10: 87-94. 27. Boviatsis EJ, Stavrinou LC, Kouyialis AT, et al. Spinal synovial cysts: Pathogenesis, diagnosis and surgical treatment in a series of seven cases and literature review. Eur Spine J 2008;17:831-837. 28. El Shazly AA, Khattab MF. Surgical excision of a juxtafacet cyst in the lumbar spine: A report of thirteen cases with long-term follow up. Asian J Neurosurg 2011;6:78-82. 29. Ayberk G, Ozveren F, Go ¨k B, et al. Lumbar synovial cysts: Experience with nine cases. Neurol Med Chir (Tokyo) 2008;48:298-303; discussion 303. 30. Me ´tellus P, Fuentes S, Dufour H, Do L, Figarella-Branger D, Grisoli F. An unusual presentation of a lumbar synovial cyst: Case report. Spine 2002;27:E278-E280. 31. Epstein NE. Lumbar synovial cysts: A review of diagnosis, surgical management, and outcome assessment. J Spinal Disord Tech 2004; 17:321-325. 32. Salmon B, Martin D, Lenelle J, Stevenaert A. Juxtafacet cyst of the lumbar spine. Clinical, radiological and therapeutic aspects in 28 cases. Acta Neurochir (Wien) 2001;143:129-134. 33. Apostolaki E, Davies AM, Evans N, Cassar-Pullicino VN. MR imaging of lumbar facet joint synovial cysts. Eur Radiol 2000;10: 615-623. 34. Me ´tellus P, Fuentes S, Adetchessi T, et al. Retrospective study of 77 patients harbouring lumbar synovial cysts: Functional and neurological outcome. Acta Neurochir (Wien) 2006;148:47-54; discussion 54.
Disclosure R.M. Department of Medical Imaging, University of Arizona, Tucson, AZ Disclosure: nothing to disclose J.P. Department of Radiology, University of Washington, Seattle, WA Disclosure: nothing to disclose S.A.M. University of Arizona College of Medicine, Tucson, AZ Disclosure: nothing to disclose
G.J.G.P.-C. Department of Medical Imaging, University of Arizona, 1501 N. Campbell Avenue, Tucson, AZ 85724. Address correspondence to: G.J.G.P.-C.; e-mail:
[email protected] Disclosure: nothing to disclose
Submitted for publication February 23, 2018; accepted February 23, 2018.
