Clinical Orthopedic Imaging

High-Resolution 3T MR Neurography of the

Avneesh Chhabra, M.D.; Aaron Flammang, MBA, BS; John A. Carrino, M.D., M.P.H.

Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, MD, USA

1A 1B 1C

1A–C Lumbosacral Plexus 3T MR Neurography evaluation: Isotropic multiplanar reformats from 3D T2 SPACE (1A–1C).

Abstract The lumbosacral (LS) plexus is a series of trum of pathologies along with their ings and electrodiagnostic study results. convergences and ramifications respective imaging findings using However, differentiation of LS plexopathy that provide motor and sensor innerva- 3 Tesla MR Neurography. from spine related abnormality and tion to pelvis and lower extremities. LS definition to type, location and extent plexopathy is a serious condition caused Introduction of pathology often remains a diagnostic by a variety of pathologies. Magnetic The lumbosacral (LS) plexus is com- challenge due to deep location of the Resonance Neurography is an important prised of an intricate architecture of and variable regional muscle modality for evaluation of LS plexopathy nerves that supply the pelvis and lower innervation [1, 2]. With current high due to variable clinical presentations extremity. It can be subject to a variety resolution 3 Tesla (T) Magnetic Reso- and deep location leading to suboptimal of pathologies, which may result in LS nance Neurography (MRN) techniques, accessibility of the plexus to electrodiag- plexopathy, a clinical syndrome that diagnostic evaluation of large LS plexus nostic studies. This article describes the includes motor and sensory distur- branches, such as sciatic and femoral role of MR Neurography in evaluation of bances. The diagnosis of LS plexopathy nerves, as well as smaller segments, the LS plexus and illustrates the spec- has traditionally relied on clinical find- such as nerve roots convergences and

26 MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world Orthopedic Imaging Clinical

1D 1E

1F 1G

1D–G Coronal reconstructed 3D STIR SPACE (1D) showing sciatic nerves (arrows). Axial T1w (1E) and T2 SPAIR (1F) images showing bilateral femoral nerves (arrows) and lateral femoral cutaneous nerves (arrowheads). MIP coronal 3D STIR SPACE (1G) image showing bilateral LS plexus nerve roots, femoral nerves (arrowheads) and sciatic nerves (arrows).

peripheral nerves is feasible, aiding in ventral rami of lumbar (L1–4 +/– T12), and lateral femoral cutaneous nerves pre-surgical evaluation and appropriate sacral (S1–4 and LS trunk, L4–S1) and (L2, 3)]. All branches exit lateral to the patient management [3, 4]. This article the lower sacrococcygeal (S2–4 and C1) psoas muscle and course under the provides a pertinent discussion of the nerves, respectively [5]. The plexus is , except the obturator LS plexus anatomy, current role of MRN formed lateral to the intervertebral nerve and LS trunk, which exit medial to in evaluation of plexopathy and foramina and various branches course the psoas muscle. The gives describes the respective imaging find- through the . The rise to anterior branches, namely the ings of various pathologies using 3T MR ventral rami are further split into ante- tibial part of the (L4–S3), Neurography. rior and posterior divisions. The anterior (S1–4) and medial part divisions give rise to the iliohypogastric of the posterior femoral cutaneous Anatomic considerations (L1), ilioinguinal (L1), (S1–3) and, posterior branches, The LS plexus is comprised of lumbar (L1-L2) and obturator nerves (L2–4). namely the common peroneal part of the plexus, sacral plexus and the pudendal The posterior divisions combine to form sciatic nerve (L4–S2), superior (L4–S1) plexus, with contributions from the the posterior branches [femoral (L2–4) and inferior gluteal nerves (L5–S2),

MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world 27 Clinical Orthopedic Imaging

Table 1: S The 3T MR imaging protocol employed in our institution of the evaluation of the lumbosacral plexus.

Sequence Slice Field-of-view Voxel size (mm3) TR/ TE (ms) Turbo factor (cm)

Axial T1 TSE BL 33 0.64 800/12 6

Axial T2 SPAIR BL 33 1.00 4500/80 17

Coronal PD SPAIR BL 36-38 0.6 4980/38 7

Coronal T1 TSE BL 36-38 0.5 550/10 3

3D Coronal STIR SPACE BL 36-38 1.45 1500/103 61

Lumbar 3D Sagittal T2 SPACE 28 1.45 1000/99 69 spine

Coronal 3D VIBE * BL 36-38 0.58 4.39/2.01 –

Abbreviations are: TSE = Turbo Spin Echo, SPAIR = spectral adiabatic inversion recovery, STIR = short tau inversion recovery, 3D SPACE = three-dimen- sional Sampling Perfection with Application optimized Contrasts using constantly varying flip angle Evolutions, VIBE = Volume Interpolated Breath- hold Exam (* optional), BL = bilateral

lateral part of the posterior femoral clinical and laboratory findings. MRN guidance during perineural and intra- cutaneous nerve (S1–3) and the nerve may be used in the latter case to confirm muscular medication injection. to the piriformis muscle (L5, S2). The lumbar plexitis / plexopathy in clinically above two plexuses connect via the LS confusing presentation and underlying Clinical fi ndings trunk to form the LS plexus [2, 5]. known systemic condition. In addition, a LS plexopathy most often presents with primary or idiopathic form of LS plexop- asymmetric weakness, pain and/or par- Pathologic conditions and athy may occur, possibly due to altered esthesias in the lower extremities involv- indications of MRN immunological response and is consid- ing multiple contiguous LS nerve root The LS plexus is relatively protected by ered analogous to idiopathic brachial distributions. Generally, unilateral local- the axial skeleton and entrapment neu- plexopathy [6–8]. The entity has a favor- ization of symptoms indicates a local ropathy is much less common than bra- able outcome and spontaneous recov- pathology, whereas bilateral symptoms chial plexopathy. It is considered as the ery, whereas its diagnosis is based upon suggest a systemic process. The clinical counterpart of the brachial plexus in the exclusion of other etiologies and some- picture often varies depending upon the lower body and is affected by similar times may require confirmation with location and degree of plexus involve- types of diseases. The LS plexus may be MRN in case of indeterminate electrodi- ment. In cases of involvement of the involved by local processes in the viscin- agnostic results. An important indication upper nerve roots, patients predomi- ity of the plexus, such as extrinsic com- of MRN is in patients under consider- nantly present with femoral and obtura- pression by space occupying lesions, ation for surgery for peripheral nerve tor nerve symptoms. LS trunk and upper injury or infiltration by tumor / infec- lesions (piriformis syndrome/meralgia sacral plexus lesions result in foot drop tious process – which is an indication for paresthetica), post abdominal surgery depending on the extent of involvement MRN; or in systemic conditions, such entrapment of ilioinguinal/genitofemo- and weakness of knee flexion or hip as metabolic, autoimmune, vasculitis, ral nerves, or after injury to a large abduction. Sensory symptoms may vary ischemic or inflammatory disorders – branch (sciatic, femoral, obturator). based on the individual nerves involved, which are usually diagnosed based on Finally, MRN is increasingly used for which may include numbness or

28 MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world Orthopedic Imaging Clinical

2A 2B 2B 2 Normal vs abnormal LS Plexus. Coronal MIP 3D STIR SPACE images in a nor- mal subject (2A) and another sub- ject with schwan- nomatosis (arrows in 2B).

3A 3B

3 Piriformis syndrome – large LS plexus branch nerve abnormality. 33-year-old man with right buttock and pelvic pain, suspected piriformis syndrome. Coronal T1w (3A) and coronal MIP 3D STIR SPACE (3B) images through the pelvis show split right sciatic nerve by an accessory slip of the right piriformis muscle (arrow). Notice abnormal T2 hyperintensity of the sciatic nerve in keeping with entrapment neuropathy.

dysesthesia in the anterolateral thigh MRN technique and normal tures under interrogation, it is essential from lateral femoral cutaneous nerve appearances to use high resolution imaging with a involvement; in the mons and labia Compared to 1.5T systems 3 Tesla combination of 2D (dimensional) and 3D majora from genitofemoral nerve (MAGNETOM Verio and MAGNETOM Trio, isotropic spin echo type imaging for involvement and in the lower Siemens, Erlangen, Germany) imaging optimal assessment. In the presence of and inguinal area, upper medial thigh or is preferred for most MRN examinations known metal* in the area of imaging, pelvis from damage to the ilioinguinal, by the authors due to high quality scans 1.5T imaging is preferred. Table 1 and iliohypogastric, or pudendal nerves, obtained by these systems due to better Fig. 1 show the 3T MRN imaging protocol respectively. Rarely, there may be associ- signal-to-noise ratio and contrast reso- employed at Johns Hopkins for the eval- ated bowel and bladder incontinence as lution available in short imaging times. uation of the LS plexus. For fascicular well as sexual dysfunction [6–8]. Due to the relatively small nerve struc- architecture and subtle signal intensity

MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world 29 Clinical Orthopedic Imaging

changes, high- resolution 2D axial T1w planning and understanding of the adjacent vascular signal intensity, or and T2 SPAIR (Spectral Adiabatic Inver- referring physicians. Side-side imaging asymmetric SI to the other side, given sion Recovery) images are ideal. Fascicu- differences of the nerves can also be variations due to non-uniform fat satura- lar appearance of nerves is consistently highlighted on maximum intensity pro- tion); as well as indirect features such as seen with T2 SPAIR images in larger jection (MIP) images. Gadolinium admin- effacement of perineural fat planes due branches, such as femoral nerves and istration is reserved for cases of sus- to focal fibrosis/mass lesions (Figs. 2, 3) sciatic nerves, as well as in smaller pected neoplasm, inflammation, diffuse and regional muscle denervation nerves that are affected and enlarged polyneuropathy, neurocutaneous syn- changes (edema like T2 signal alteration due to neuropathy, such as lateral femo- drome, or post-operative complication in acute and subacute cases to fatty ral cutaneous and genitofemoral nerves. [9–13]. Additional coronal T1w and replacement and atrophy in chronic 2D imaging is complemented by isotro- STIR/PD SPAIR images aid in detection of cases). MRN is useful for detecting the pic 3D images reconstructed in planes lesions along the long axis of the nerves, individual segmental nerve abnormali- perpendicular and longitudinal to the side-to-side comparison of the nerve ties (enlarged or asymmetrically T2 nerves in question. 3D imaging (SPACE – morphology and signal intensity (gener- hyperintense) in cases of plexitis/ Sampling Perfection with Application ally symmetrical), as well as for depic- plexopathy or nerve injury. Similar to optimized Contrasts using constantly tion of other incidental findings in rela- brachial plexus imaging, minimal varying flip angle Evolutions) allows tion to hips or spine. SPAIR produces increased nerve T2 signal intensity alone multiplanar and curved planar reforma- higher SNR and is less prone to pulsation should be perceived with caution, as tions. Two types of 3D imaging are per- artifacts than STIR imaging, and is also magic-angle artifact is a well-recognized formed, focusing in two different loca- more SAR favorable at 3T imaging [3, 4]. artifact in LS plexus MR imaging [3, 4]. tions with two different purposes, 3D MRN is also useful in differentiating the STIR SPACE for the LS plexus (from L2-3 MR Neurography fi ndings of LS plexopathy (nerve abnormality starting level to lesser trochanter of femurs), plexopathy distal to the neural foramina, and often while T2 SPACE (from L2-S2) is used for MRN assessment of the LS plexus relies involving multiple nerve roots) from the lumbar spine, as spondylosis is a on the evaluation of direct morphologic lumbar spondylosis (presence of sub- major confounder in the diagnosis of features, such as altered nerve size, stantial spondylosis, disc herniations, peripheral nerve pathology (Fig. 1). abnormal fascicular morphology intraspinal mass, and nerve abnormality 3D imaging shows the lesions along the (disrupted, effaced or enlarged) and starting from within and immediately long axis of the nerve, course devia- focal or diffuse deviations in nerve distal to the neural foraminal level in a tions, focal neuroma, nerve gap in cases course. T2 signal intensity (SI) changes distribution of the narrowed foramina). of injury, etc. for better pre-operative (signal alterations approaching the It is also worth mentioning that MRN may help exclude LS plexopathy in clini- cally confusing cases by demonstrating 4 normal symmetrical appearance of bilat- 4 Right femoral eral nerve segments. In trauma cases, it nerve transection – large LS plexus branch is critical to demonstrate whether the nerve abnormality. injury is merely a stretch injury (merely 64-year-old man with T2 signal alterations) with nerve conti- right leg weakness nuity; or if there is neuroma formation following recent sur- (focal enlargement of the nerve with gery. Coronal MIP 3D STIR SPACE image effaced fascicular appearance) or nerve through the pelvis root avulsion or nerve discontinuity, shows abrupt termi- which may be indications for surgery nation of the right (Fig. 4). Peripheral nerve sheath tumors in keep- ing with transection are depicted as focal or fusiform (arrow) (Sunderland enlargements of the nerves, and may Grade V injury). variably demonstrate classic signs, such as the tail, target, fascicular, bag of worms and split-fat signs. Differentia- tion between benign and malignant peripheral nerve sheath tumors is generally not reliable by imaging, although large size, ill-defined margins, peritumoral edema, significant interval growth and internal heterogeneity,

30 MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world Orthopedic Imaging Clinical

5A 5B

5 Genitofemoral nerve entrapment – small LS plexus branch nerve abnormality. 50-year-old man with right inguinal and scrotal pain, following a prior right inguinal hernia repair. Axial T2 SPAIR (5A) and oblique coronal MIP 3D STIR SPACE (5B) images through the pelvis show abnormally enlarged and hyperintense right genitofemoral nerve (arrows), with most abnormality at the site of previous hernia repair in keeping with entrapment neuropathy.

6A 6B

6 Right pudendal and sciatic Neuropathy – small LS plexus branch nerve abnormality. 61-year-old man with right pelvic pain, suspected pudendal neuralgia. Axial T2 SPAIR image through the pelvis shows grade I/II strain of the right obturator internus muscle (large arrow) with mild hyperintensity of the right pudendal nerve (small arrow) and right sciatic nerve (dotted arrows) in keeping with acute neuropathy.

especially in neurofibromas, are percutaneous biopsy/ surgical biopsy/ Lumbosacral plexus branch suspicious for malignancy. In those cases, resection. Finally, MRN aids in differentia- anatomy and pathology a combination of clinical (new onset or tion of radiation neuropathy (diffuse Current high-resolution 3T techniques increasing pain / neurological deficit), nerve signal intensity alterations and allow depiction of internal nerve pathol- MRN imaging findings (as above), as well enhancement in a geographic distribu- ogy of normal sized large branches, such 18 as F FDG PET uptake (SUVmax >3–4 and tion corresponding to the radiation field) as sciatic (Fig. 3), obturator, femoral increased uptake on delayed imaging) are from recurrent mass lesion (focal enhanc- (Fig. 4), various lumbosacral nerve roots used to make a clinical decision about ing lesions) [11–14]. as well as enlarged smaller branches,

MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world 31 Clinical Orthopedic Imaging

such as ilioinguinal, genitofemoral 7A 7B (Fig. 5) and pudendal (Figs. 6, 7) nerves. Many of the smaller nerves are sensory nerves, and electrodiagnostic studies are usually not useful for their assessment. Nerve blocks have also been variably used, more so for therapeutic effect rather than for diagnosis of pathology. MRN may detect lesions within (diffuse enlargement proximal to entrapment, neuroma, etc.) or surrounding these nerves (focal fibrosis/mass lesion), thereby impacting patient management. Iatrogenic insults, such as during lapa- rotomy, lymph node dissection, difficult 7 Chronic pudendal Neuralgia – small LS plexus branch nerve abnormality. 41-year-old woman parturition, hernia repair, etc are the with pelvic pain, right > left for many months. Coronal T1w (7A) and axial T2 SPAIR (7B) images leading cause of injury to these fine through the pelvis show bilateral pelvic scarring (right > left), along the expected course of the nerves. MRN may be used to detect focal pudendal nerves, causing entrapment (arrows). Notice asymmetrically prominent right pudendal neurovascular bundle (arrow). fibrosis along the course of these nerves and their branches, which may be used *In the US, metal near or in the MR system must be labeled to guide neurolysis. Such a procedure as MR-safe or conditional (with conditions stated). may give back patients’ necessary sensa- tion or provide pain relief. Finally, MRN References may be used to provide guidance for 1 Gebarski KS, Gebarski SS, Glazer GM, Samuels 11 Chhabra A, Williams EH, Wang KC, Dellon AL, BI, Francis IR. The lumbosacral plexus: anatomic- Carrino JA. MR neurography of neuromas related perineural (local anesthetic and steroids) radiologic-pathologic correlation using CT. to nerve injury and entrapment with surgical and intramuscular medication (e.g. Radiographics. 1986;6(3):401-25. correlation. AJNR Am J Neuroradiol. 2010 Sep; Botulinium Toxin) injections. It is impor- 2 Petchprapa CN, Rosenberg ZS, Sconfienza LM, 31(8):1363-8. Epub 2010 Feb 4. tant to know that an appropriately Cavalcanti CF, Vieira RL, Zember JS. MR imaging of 12 Chhabra A, Soldatos T, Durand D, Carrino JA, performed image guided negative block / entrapment neuropathies of the lower extremity. McCarthy EF, Belzberg AJ. The role of MRI in the Part 1. The pelvis and hip. Radiographics. diagnostic evaluation of malignant peripheral placebo controlled or graded positive 2010;30(4):983-1000. nerve sheath tumors. Indian J Cancer. 2011: nerve block confers more specificity to 3 Chhabra A, Lee PP, Bizzell C, Soldatos T. 3 Tesla MR (in press). the diagnosis rather than a single posi- neurography-technique, interpretation, and pit- 13 Taylor BV, Kimmel DW, Krecke KN, Cascino TL. Mag- tive block. Few studies have however, falls. Skeletal Radiol. 2011 May 6. [Epub ahead of netic resonance imaging in cancer-related lumbo- sacral plexopathy. Mayo Clin Proc. 1997;72(9):823-9. shown the therapeutic value of these print]. 4 Chhabra A, Andreisek G, Soldatos T, Wang KC, 14 Whiteside JL, Barber MD, Walters MD, Falcone T. blocks [15–22]. Flammang AJ, Belzberg AJ, Carrino JA. MR Neu- Anatomy of ilioinguinal and iliohypogastric nerves rography: Past, Present, and Future. AJR Am J in relation to trocar placement and low transverse Conclusion Roentgenol. 2011 Sep;197(3):583-91. incisions. Am J Obstet Gynecol. 2003;189(6): In the evaluation of LS plexopathy, 3T 5 Kirchmair L, Lirk P, Colvin J, Mitterschiffthaler G, 1574-8; discussion 8. Moriggl B. and psoas major 15 Klaassen Z, Marshall E, Tubbs RS, Louis RG, Jr., MRN provides high quality imaging and muscle: not always as expected. Reg Anesth Pain Wartmann CT, Loukas M. Anatomy of the ilioingui- is a valuable adjunct to clinical examina- Med. 2008;33(2):109-14. nal and iliohypogastric nerves with observations of tion and electrodiagnostic tests as it can 6 Evans BA, Stevens JC, Dyck PJ. Lumbosacral plexus their contributions. Clin Anat. offer anatomic information and lesion neuropathy. Neurology. 1981;31(10):1327-30. 2011;24(4):454-61. assessment otherwise unattainable by 7 Sander JE, Sharp FR. Lumbosacral plexus neuritis. 16 Hu P, Harmon D, Frizelle H. Ultrasound guidance Neurology. 1981;31(4):470-3. for ilioinguinal/ block: a pilot other modalities. 8 Hollinger P, Sturzenegger M. Chronic progressive study. Ir J Med Sci. 2007;176(2):111-5. primary lumbosacral plexus neuritis: MRI findings 17 Tipton JS. Obturator neuropathy. Curr Rev and response to immunoglobulin therapy. Musculoskelet Med. 2008;1(3-4):234-7. J Neurol. 2000;247(2):143-5. 18 Beltran LS, Bencardino J, Ghazikhanian V, Beltran J. Contact 9 Maravilla KR, Bowen BC. Imaging of the peripheral Entrapment neuropathies III: lower limb. Semin Avneesh Chhabra, M.D., DNB : evaluation of peripheral neurop- Musculoskelet Radiol. 2010;14(5):501-11. Assistant Professor Radiology & athy and plexopathy. AJNR Am J Neuroradiol. 19 Patijn J, Mekhail N, Hayek S, Lataster A, van Kleef orthopedic Surgery 1998;19(6):1011-23. M, Van Zundert J. Meralgia Paresthetica. Pain Russell H. Morgan Department of 10 Thawait SK, Chaudhry V, Thawait GK, Wang KC, Pract. 2011;11(3):302-8. Radiology and Radiological Science Belzberg A, Carrino JA, Chhabra A. High-Resolu- 20 Chhabra A, Gustav A, Soldatos T, Wang KC, Johns Hopkins Medical Institutions tion MR Neurography of Diffuse Peripheral Nerve Belzeberg AJ, Carrino JA. 3T hihg-resolution MR [email protected] Lesions. AJNR Am J Neuroradiol. 2010 Nov 24. Neurography of sciatic neuropathy. AJR 2011 [Epub ahead of print]. (in press).

32 MAGNETOM Flash · 3/2011 · www.siemens.com/magnetom-world