Peroneal Nerve: Normal Anatomy and Pathologic Findings on Routine MRI of the Knee
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Insights Imaging (2013) 4:287–299 DOI 10.1007/s13244-013-0255-7 PICTORIAL REVIEW Peroneal nerve: Normal anatomy and pathologic findings on routine MRI of the knee F. R. A. Van den Bergh & F. M. Vanhoenacker & E. De Smet & W. Huysse & K. L. Verstraete Received: 10 February 2013 /Revised: 12 April 2013 /Accepted: 18 April 2013 /Published online: 25 May 2013 # The Author(s) 2013. This article is published with open access at Springerlink.com Abstract Teaching Points Background Peroneal nerve lesions are not common and are • Six anatomical features contribute to the vulnerability of often exclusively assessed clinically and electromyographically. the peroneal nerve around the knee. Methods On a routine MR examination without dedicated • MR signs of muscle denervation within the anterior com- MR-neurography sequences the peroneal nerve can readily partment are important secondary signs for evaluation of be assessed. Axial T1-weighted sequences are especially the peroneal nerve. helpful as they allow a good differentiation between the • The most common lesions of the peroneal nerve are nerve and the surrounding fat. traumatic or compressive. Results The purpose of this article is to review the normal • Intraneural ganglia originate from the proximal anatomy and pathologic conditions of the peroneal nerve tibiofibular joint. around the knee. • Axial T1-weighted images are the best sequence to visu- Conclusion In the first part the variable anatomy of the alise the peroneal nerve on routine MRI. peroneal nerve around the knee will be emphasized, followed by a discussion of the clinical findings of peroneal Keywords MR . Peroneal nerve . Denervation . Knee . neuropathy and general MR signs of denervation. Six ana- Proximal tibiofibular joint . Intraneural ganglion tomical features may predispose to peroneal neuropathy: paucity of epineural tissue, biceps femoris tunnel, bifurca- tion level, superficial course around the fibula, fibular tunnel Introduction and finally the additional nerve branches. In the second part we discuss the different pathologic conditions: accidental Magnetic resonance imaging (MRI) of the knee joint has and surgical trauma, and intraneural and extraneural com- become a very important imaging tool for assessment of pressive lesions. knee pain in daily routine. Most clinical inquiries are about menisci, cartilage or ligaments of the knee joint. Peroneal nerve lesions are rather uncommon and are usually exclu- : : F. R. A. Van den Bergh F. M. Vanhoenacker (*) E. De Smet sively evaluated by clinical and/or electrophysiological ex- Department of Radiology, AZ Sint-Maarten Duffel-Mechelen, amination. Because MRI provides exquisite soft tissue campus Duffel, Rooienberg 25, detail, the peroneal nerve can often be well visualised, even 2570 Duffel, Belgium e-mail: [email protected] on routine MR sequences. In most centres, a combination of : coronal, sagittal, axial fat-suppressed intermediate weighted F. M. Vanhoenacker E. De Smet sequences and a sagittal T1-weighted sequence is used for Department of Radiology, University Hospital Antwerp, routine imaging of the knee. Adding an axial T1-weighted Wilrijkstraat 10, 2650 Edegem, Belgium sequence (WI) may be helpful in evaluation of the course of : : : the peroneal nerve branches and may enhance the conspi- F. R. A. Van den Bergh F. M. Vanhoenacker W. Huysse cuity for peroneal nerve lesions. It should be considered as a K. L. Verstraete first step in case of a suspected peroneal nerve lesion. Faculty of Medicine and Health Sciences, Ghent University, De Pintelaan 185, Specific MR neurography sequences have shown their util- 9000 Ghent, Belgium ity for evaluation of peripheral nerves and can be used for a 288 Insights Imaging (2013) 4:287–299 more complete workup, at both 1.5 and 3 T [1]. The purpose identified on axial T1-WI as small bundles of fascicles of this paper is, however, to emphasise the strength of cushioned in surrounding fatty tissue (Fig. 1c, d, e and f). meticulous analysis of routine MR sequences in the diagno- The peroneal nerve has several unique anatomical fea- sis of peroneal nerve lesions about the knee. In the first part tures making it susceptible to injury. we focus on the relevant anatomy of the peroneal nerve and The first is the relative paucity of epineural supporting general clinical and MR features of peroneal neuropathy. tissue, rendering the nerve more susceptible to compression Electromyography is only briefly addressed, as this is be- [2–5]. yond the scope of this pictorial review. The second consists of a variant of its course along the In the second part we present the most common lesions distal biceps femoris muscle. A tunnel can be formed between involving the peroneal nerve around the knee. the biceps femoris muscle and the lateral gastrocnemius mus- cle (Fig. 2). This occurs when there is a more posterior or distal extension of the short head of the biceps femoris muscle Anatomic background and, rarely, when there is a more distal extension of the long head of the biceps femoris muscle. This tunnel results in less The common peroneal nerve is the lateral division of the fatty cushioning of the peroneal nerve and is considered a sciatic nerve. It courses from the posterolateral side of the predisposing factor for neuropathy [6]. knee around the biceps femoris tendon and the fibular head A third feature is a more proximal bifurcation of the pero- to the anterolateral side of the lower leg. Its relationship to neal nerve (Fig. 3). This is found in 10 % of preserved the most important landmarks is illustrated on Fig. 1.On specimens and makes the peroneal nerve more prone to injury MRI the peroneal nerve and its branches can most easily be with arthroscopic inside-out lateral meniscal repair [7, 8]. Fig. 1 Normal anatomy of the peroneal nerve at the level of the the short head of the biceps femoris (B) and the lateral head of the posterolateral corner of the right knee. Schematic drawing of a sagittal gastrocnemius muscle (G), a site of possible entrapment in case of (a) and coronal (b) view with corresponding axial T1-WI of a right variant course of the short head of the biceps femoris. The fascicles of knee; the levels are indicated by the transparent boxes. On the sche- the deep and superficial peroneal nerve can sometimes be discerned matic drawing the nerve is seen branching off the sciatic nerve, turning from this level on, the former more anteriorly, the latter more posteri- around the biceps femoris muscle (BF), passing through the peroneal orly, corresponding to the location of the anterior and lateral compart- tunnel between the insertion of the peroneus longus muscle (PL) and ment of the lower leg. Axial T1-WI at the level of the fibular head (e). the fibula. As it exits the tunnel, it trifurcates in a deep (D) and The common peroneal nerve (white arrow) is found posteriorly and can superficial peroneal nerve (S) and a recurrent or articular branch (A). be traced by the fat around it. The peroneus longus (*) and anterior The articular branch is the entrance port for intraneural ganglia origi- tibial muscle (**) are already seen at the most proximal parts of the nating from the proximal tibiofibular joint (see the section on lateral and anterior compartments. Axial T1-WI at the level just below intraneural ganglia). Axial T1-WI at the level of the distal femur (c) the fibular neck (f) shows the superficial and deep peroneal nerve shows the common peroneal nerve (white arrow) and the tibial nerve (white arrow). Because of their more horizontal course at this level, (black arrow) as they branch off the sciatic nerve. Note the intimate they are more difficult to discern from each other. At the 12 o’clock relationship of the common peroneal nerve with the medial side of the position the articular branch can be visualised as a small black dot biceps femoris muscle (B). Axial T1-WI at the level of the femoral surrounded by hyperintense fat (arrowhead). a adapted with permis- condyles (d) shows the common peroneal nerve (white arrow) between sion from ref [50]. b adapted with permission from ref [10] Insights Imaging (2013) 4:287–299 289 The fifth feature is the fibular tunnel is formed between the musculo-aponeurotic arch of the peroneus longus and soleus tendon and the bony floor of the proximal fibula (Fig. 1). Entrapment or impingement in this tunnel occurs mainly between the fibres of the peroneus longus and the fibular neck and is typically exacerbated by forced inversion of the foot, stretching the peroneal nerve [5, 9, 10]. The osteofibrous tunnel between the peroneus longus muscle and the fibula can be tightened by an ossification at the peroneus longus muscle origin or tug lesion (Fig. 4). It should be considered when peroneal nerve neuropathy is present clinically without any other obvious cause. A pero- neal tug lesion typically occurs on the lateral side of the fibula, while a soleus tug lesion occurs on the medial side [11, 12]. The typical location allows differentiation with an osteochondroma [11]. The sixth and last feature is the additional branches at the level of the knee joint. The most important is the articular branch (also called recurrent branch). When exiting the fibular tunnel the peroneal nerve typically trifurcates in the deep and superficial peroneal nerve and a smaller articular branch (Fig. 1). This articular branch provides sensory in- Fig. 2 Schematic drawing of the popliteal fossa (right knee). A tunnel can formation from the proximal tibiofibular joint and has been be formed between the short head of the biceps femoris (SH) and the lateral shown to be a very common location and entrance port for head of the gastrocnemius muscle (GM). Long head of the biceps femoris intraneural ganglia [13]. In addition to the articular branch, muscle (LH), sciatic nerve (S), tibial nerve (T) and peroneal nerve (P).