NEUROMUSCULAR IMAGES
Muscle Nerve 00: 00–00, 2017
EXTRANEURAL GANGLION CYST AS A RARE CAUSE FOR FOOTDROP SUSAN WALKER, MBBS, FRACP,1 DUNCAN SNODGRASS, MBBS, FRANZCR,2 DARREN CHEN, MBBS, FRACS,3 and WILLIAM HUYNH, PhD, FRACP1 1
Department of Neurology, Prince of Wales Hospital, Barker Street, Randwick, Sydney, 2031, Australia PRP Diagnostic Imaging, Sydney, Australia 3 Sydney Knee Specialists, Sydney, Australia 2
FIGURE 1. Proton density (A) and fat-saturated (B) axial MRI images at the level of the fibular neck, clearly demonstrating the multilocular ganglion cyst arising from the tibiofibular joint predominantly anterior to the interosseous membrane and extending across the deep aspect of the anterior muscle compartment. Its lateral extension is shown to be compressing the common peroneal nerve. Sagittal fat-saturated image (C) of the proximal fibula shows the ganglion cyst compressing the common peroneal nerve (dashed lines) posteriorly. Coronal fat-saturated image (D) shows the cyst epicenter arising from the tibiofibular joint, confirming its extraneural origin. [Color figure can be viewed at wileyonlinelibrary.com] Key words: extraneural ganglion cyst; foot drop; ganglion cyst; peroneal nerve Funding: No funding was received for this research. Conflicts of Interest: None of the authors have any conflict of interest to disclose. Correspondence to: W. Huynh; e-mail: [email protected] C 2017 Wiley Periodicals, Inc. V
Published online 12 August 2017 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.25765
A 62-year-old man presented with a 2-week history of right footdrop and lateral knee pain. Examination revealed weakness of right ankle dorsiflexion (Medical Research Council grade 2) and eversion (grade 4) with preserved tendon reflexes. Nerve conduction studies revealed focal conduction block and slowing of right peroneal nerve conduction velocity across the fibular neck. MUSCLE & NERVE
Month 2017
E1
MRI demonstrated an extraneural ganglion cyst causing extrinsic compression of the peroneal nerve at the fibular neck (Fig. 1). Intraoperatively, the cyst was confirmed to originate from the tibiofibular joint and to cause extrinsic compression of the peroneal nerve. Excision of the cyst was followed by gradual improvement in power within days and normalization within 2 months, associated with resolution of electrophysiological abnormalities. Histopathology confirmed the extraneural location of the cyst. A ganglion cyst is delineated by connective tissue filled with gelatinous fluid. The etiology is unclear, but the cysts tend to occur at areas of mechanical stress.1 Although intraneural cysts are not uncommon, extraneural cysts appear to be rare causes of peroneal neuropathy.2 Ganglion cysts demonstrate T1 hypointensity and T2 hyperintensity on MRI. Intraneural cysts
E2
are tubular structures, contained within the nerve. Extraneural cysts have a thin, hypointense wall and may have loculations with internal septa.3 Recovery of peroneal nerve function after resection is generally favorable. The present case highlights the role of neuroimaging in patients presenting with acute foot drop (particularly in those without an obvious predisposing factor such as trauma), and has implications for management and prognosis.
REFERENCES 1. Kim JY, Jung SA, Sung MS, Park YH, Kang YK. Extra-articular soft tissue ganglion cyst around the knee: focus on the associated findings. Eur Radiol 2004;14:106–111. 2. Visser LH. High-resolution sonography of the common peroneal nerve: detection of intraneural ganglia. Neurology 2006;67:1473– 1475. 3. Van den Bergh FR, Vanhoenacker FM, De Smet E, Huysse W, Verstraete KL. Peroneal nerve: normal anatomy and pathologic findings on routine MRI of the knee. Insights Imaging 2013;4:287–299.
MUSCLE & NERVE
Month 2017
Muscle Nerve 00: 00–00, 2017
EXTRANEURAL GANGLION CYST AS A RARE CAUSE FOR FOOTDROP SUSAN WALKER, MBBS, FRACP,1 DUNCAN SNODGRASS, MBBS, FRANZCR,2 DARREN CHEN, MBBS, FRACS,3 and WILLIAM HUYNH, PhD, FRACP1 1
Department of Neurology, Prince of Wales Hospital, Barker Street, Randwick, Sydney, 2031, Australia PRP Diagnostic Imaging, Sydney, Australia 3 Sydney Knee Specialists, Sydney, Australia 2
FIGURE 1. Proton density (A) and fat-saturated (B) axial MRI images at the level of the fibular neck, clearly demonstrating the multilocular ganglion cyst arising from the tibiofibular joint predominantly anterior to the interosseous membrane and extending across the deep aspect of the anterior muscle compartment. Its lateral extension is shown to be compressing the common peroneal nerve. Sagittal fat-saturated image (C) of the proximal fibula shows the ganglion cyst compressing the common peroneal nerve (dashed lines) posteriorly. Coronal fat-saturated image (D) shows the cyst epicenter arising from the tibiofibular joint, confirming its extraneural origin. [Color figure can be viewed at wileyonlinelibrary.com] Key words: extraneural ganglion cyst; foot drop; ganglion cyst; peroneal nerve Funding: No funding was received for this research. Conflicts of Interest: None of the authors have any conflict of interest to disclose. Correspondence to: W. Huynh; e-mail: [email protected] C 2017 Wiley Periodicals, Inc. V
Published online 12 August 2017 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.25765
A 62-year-old man presented with a 2-week history of right footdrop and lateral knee pain. Examination revealed weakness of right ankle dorsiflexion (Medical Research Council grade 2) and eversion (grade 4) with preserved tendon reflexes. Nerve conduction studies revealed focal conduction block and slowing of right peroneal nerve conduction velocity across the fibular neck. MUSCLE & NERVE
Month 2017
E1
MRI demonstrated an extraneural ganglion cyst causing extrinsic compression of the peroneal nerve at the fibular neck (Fig. 1). Intraoperatively, the cyst was confirmed to originate from the tibiofibular joint and to cause extrinsic compression of the peroneal nerve. Excision of the cyst was followed by gradual improvement in power within days and normalization within 2 months, associated with resolution of electrophysiological abnormalities. Histopathology confirmed the extraneural location of the cyst. A ganglion cyst is delineated by connective tissue filled with gelatinous fluid. The etiology is unclear, but the cysts tend to occur at areas of mechanical stress.1 Although intraneural cysts are not uncommon, extraneural cysts appear to be rare causes of peroneal neuropathy.2 Ganglion cysts demonstrate T1 hypointensity and T2 hyperintensity on MRI. Intraneural cysts
E2
are tubular structures, contained within the nerve. Extraneural cysts have a thin, hypointense wall and may have loculations with internal septa.3 Recovery of peroneal nerve function after resection is generally favorable. The present case highlights the role of neuroimaging in patients presenting with acute foot drop (particularly in those without an obvious predisposing factor such as trauma), and has implications for management and prognosis.
REFERENCES 1. Kim JY, Jung SA, Sung MS, Park YH, Kang YK. Extra-articular soft tissue ganglion cyst around the knee: focus on the associated findings. Eur Radiol 2004;14:106–111. 2. Visser LH. High-resolution sonography of the common peroneal nerve: detection of intraneural ganglia. Neurology 2006;67:1473– 1475. 3. Van den Bergh FR, Vanhoenacker FM, De Smet E, Huysse W, Verstraete KL. Peroneal nerve: normal anatomy and pathologic findings on routine MRI of the knee. Insights Imaging 2013;4:287–299.
MUSCLE & NERVE
Month 2017
