- Email: [email protected]
Direct and indirect MRI findings in ganglion cysts of the common peroneal nerve
ClinicalRadiology(1995) 5tl, 168-169
Direct and Indirect MRI Findings in Ganglion Cysts of the Common Peroneal Nerve F. V. C O A K L E Y , D. B. F I N L A Y , W. M. H A R P E R * a n d M. J. A L L E N t
Department of Radiology, Leicester Royal Infirmary, *Department of Orthopaedics, Glenfield Hospital, and tDepartment of Sports Medicine, Leicester General Hospital, Leicester MRI findings in three cases of ganglion cyst of the common peroneal nerve are presented. In each case the cyst was imaged as an oval structure in transverse section adjacent to the fibular neck. The cyst extended in a tubular fashion over several slices with an inferior extension towards the superior tibiofibular joint. Signal intensity was intermediate on T1- and high on T2-weighted images. In addition, increased signal on both T1- and T2-weighted images was noted throughout the peroneal compartment and was associated with clinical and EMG evidence of denervation. This has not been previously described but may be an important indirect sign which, when seen, should prompt a careful search in the region of the fibular neck for an underlying ganglion cyst of the common peroneal nerve. Coakley, F.V., Finlay, D.B., H a r p e r , W . M . & Allen, M.J. (1995). Clinical Radiology 50, 168-169. Direct a n d Indirect M R I F i n d i n g s in G a n g l i o n Cysts o f the C o m m o n P e r o n e a l Nerve
Accepted for Publication 2 November 1994 T h e c o m m o n p e r o n e a l (fibular or lateral popliteal) nerve arises as a b r a n c h o f the sciatic nerve in the apex o f the popliteal fossa. It passes inferolaterally, medial to biceps femoris, a n d then winds laterally a r o u n d the head o f the fibula before dividing into deep a n d superficial b r a n c h e s which supply the p e r o n e a l c o m p a r t m e n t in the leg. A few small articular b r a n c h e s supply the superior tibiofibular j o i n t . G a n g l i o n cysts at the knee in the nerve are rare b u t well recognized entities [1]. They typically arise in close p r o x i m i t y to the neck o f the fibula [2]. P r e s e n t a t i o n is with pain, paraesthesia o r weakness in the territory o f the c o m m o n p e r o n e a l nerve. This clinical c o m b i n a t i o n is said to be diagnostic, whether or n o t there is a p a l p a b l e swelling at the fibular neck [3]. There has been one previous report describing the M R I findings o f p e r o n e a l nerve e n t r a p m e n t due to a g a n g l i o n cyst [4]. Three f u r t h e r cases are presented here. I n each, the cyst was imaged as t u b u l a r structure a d j a c e n t to the fibular neck. I n a d d i t i o n , in each case there was increased signal t h r o u g h o u t the p e r o n e a l c o m p a r t m e n t associated with d e n e r v a t i o n . This indirect finding m a y be a n i m p o r t a n t clue to the presence o f a n u n d e r l y i n g g a n g l i o n cyst. CASE REPORTS
Case 2. A 34-year-old man presented with a 3 month history of episodic pain in the anterior aspect of the left shin and a 1 week history of left foot drop. On examination there were signs of a common peroneal nerve palsy. EMG showed complete denervation in the deep branch of the common peroneal nerve. MRI findings were essentially the same as those in Case 1. At operation a large intraneural ganglion was found. It appeared to arise from the superior tibiofibular joint and to entwine amongst the fibres of the common peroneal nerve. Histological examination confirmed the diagnosis of a ganglion cyst. There was partial resolution of the patient's foot drop postoperatively. Case 3. A 61-year-old woman presented with an 8 month history of right foot drop associated with episodic pain in the right shin. On examination there were signs of a common peroneal nerve palsy and a palpable swellingat the fibular neck. Paraesthesia could be provoked by tapping this swelling. EMG showed a severe common peroneal nerve lesion. MRI findings were essentially the same as those in Case 1. At surgery a swelling was found in the deep branch of the common peroneal nerve and could not be separated from it. A 6 cm section of nerve was resected. Histology showed an intraneural ganglion cyst. The patient was left with a permanent foot drop.
DISCUSSION These cases illustrate the ease with which M R I images g a n g l i o n cysts of the c o m m o n p e r o n e a l nerve. The finding of a t u b u l a r structure n e a r the fibular neck extending l o n g i t u d i n a l l y over several slices with a n inferior exten-
Case 1. A 16-year-oldmale presented with a 4 week history of pain around the right knee and a 1 week history of right foot drop. On examination there were signs of a common peroneal nerve palsy. EMG showed evidence of severe but partial denervation on the common peroneal nerve territory. MRI showed a mass in close proximity to the neck of the fibula extending in a tubular fashion over several slicesand with intermediate T1 and high T2 signal intensity. There was a small inferior extension of the mass towards the superior tibiofibular joint (Figs 1 and 2). There was also increased signal throughout the peroneal compartment on both T1- and T2-weightedimages (Fig. 3). At surgery, a ganglion was found at the neck of the fibula and this was felt to be related to the superior tibiofibular joint (Fig. 4). The ganglion was dissected free and histologicalexamination confirmedthe diagnosis of a ganglion cyst. Follow-up at 4 weeks postoperatively showed the foot drop to be improving significantly. Correspondence to: Dr Fergus Coakley, Senior Registrar in Radiology, Leicester Royal Infirmary, Leicester LE1 5WW.
Fig. 1-Tl-weighted (2000/20) transverse MR images at a level just below the knee. The ganglion cyst is seen as an oval mass of intermediate signal intensity near the right fibular neck (arrowhead).
GANGLIONCYSTSOF COMMONPERONEALNERVE
169
Fig. 2 T2-weightedimage (2000/80) at the same levelas Fig. 1 showing the high signal from the cyst (arrowhead) with a small anterior extension towards the superior tibiofibularjoint. Fig. 4 lntraoperative photograph of the ganglion cyst imaged in Figs 1 3. A normal section of the common peroneal nerve is seen supported by a tape. Distally the nerve is expanded by the ganglion cyst (arrowhead).
Fig. 3-T2-weighted image (2000/80) at mid-calf level showing increased signal throughout the right peroneal compartment (arrowhead). This change is also evident, though less obvious, in Figs 1 and 2.
sion towards the superior tibiofibular joint and with intermediate T I and high T2 signal intensity was characteristic. The T 1 signal may appear higher than expected for a fluid-filled structure. This is probably because these cysts contain a mucoid glue-like material [2,5] rather than simple watery fluid. These M R I findings could conceivably suggest a venous structure; however, the confinement to a small number of contiguous slices together with t h e absence of a vein at this site normally should help in making the distinction. In addition, scanning both knees to allow comparison m a y be helpful. The finding of increased signal in the peroneal compartment in association with clinical and E M G evidence of denervation is noteworthy and has not been previously reported with ganglion cysts o f the c o m m o n peroneal nerve. Denervation is a well described [6,7] cause of such change in the M R signal from muscle, though perhaps not widely recognized. It is related to shrinkage of the denervated muscle cells with a compensatory increase in the extracellular fluid volume and perhaps also to fatty infiltration [7]. This finding was the most prominent sign, albeit indirect, in the three cases described. The finding of increased signal in the peroneal c o m p a r t m e n t should p r o m p t careful scrutiny of the region o f the fibular neck for an underlying ganglion cyst, particularly in the appropriate clinical setting. High signal intensity of skeletal muscle on T2-weighted images is also seen in inflammatory myopathies, exercise-induced change, rhabdomyolysis, c o m p a r t m e n t syndrome and muscle involvement by tumours [7]. A b n o r m a l signal intensity confined to the area supplied by a nerve and E M G findings should help differentiate these conditions from denervation, as in these three cases.
The origin of ganglion cysts found in the common peroneal nerve is controversial. The synovial theory, with which there is currently the most consensus [1], regards these lesions as genuine cysts of articular or paraarticular origin. The finding of a peduncle connecting the cyst to the superior tibiofibular joint is said to be an important point in favour of this theory [8] and in a recent review was seen in 40% of reported cases [1]. The inferior extension of the cyst towards the superior tibiofibular joint seen in all three cases described here would appear to favour this theory. This extension, if seen, is of surgical significance since it has been recommended that the cystic peduncle should preferably be removed to prevent recurrence [1]. It should be noted that while ganglion cysts contain fluid which is very similar to synovial fluid, they are not lined by synovium and do not communicate with the joint cavity [9]. These two features distinguish ganglia from synovial cysts such as Baker's cysts and the terms should not be used interchangeably in order to avoid confusion between true ganglia and synovial cysts related to joints or tendon sheaths. Unfortunately the usage o f the terms as synonyms is frequent in the literature [1,3,8]. REFERENCES
1 Nucci F, Artico M, Santora Aet al. Intraneural synovialcyst of the peroneal nerve: report of two cases and a review of the literature.
Neurosurgery 1990;26:339-344. 2 Gambari PI, Giuliani G, Poppi Met al. Ganglionic cysts of the peroneal nerve at the knee: CT and surgical correlation. Journal of Computer Assisted Tomography 1990;14(5):801-803. 3 Lagarrique J, Robert R, Resche F et al. Kystes synoviaux intranerveux du sciatique poplite externe. Neurochirurgie 1982;28:131-134. 4 Leon J, Marano G. MRI of peroneal nerve entrapment due to a ganglion cyst. Magnetic Resonance Imaging 1987;5:307-309. 5 LeijtenFS, Willen-Frans A, Puylaert JB. Ultrasound diagnosisof an intraneural ganglion of the peroneal nerve. Journal of Neurosurgery 1992;76:538-543. 6 Shabas D, Gerard G, Rossi D. Magnetic resonance imaging examination of denervated muscle. Computed Radiology 1987;11(1):9-13. 7 Uetani M, Hayashi K, Matsunaga N e t aL Denervated skeletal muscle: MR imaging. Radiology 1993;189(2):511-515. 6 Robert R, Resche F, Lajat U et al. Kyste synovial intraneural du sciatique poplite externe. Apropos d'un case. Neurochirurgie 1980;26:135-143. 9 Lichtenstein L. Tumors of synovial joints, bursae, and tendon sheaths. Cancer 1955;8:816-830.
Direct and Indirect MRI Findings in Ganglion Cysts of the Common Peroneal Nerve F. V. C O A K L E Y , D. B. F I N L A Y , W. M. H A R P E R * a n d M. J. A L L E N t
Department of Radiology, Leicester Royal Infirmary, *Department of Orthopaedics, Glenfield Hospital, and tDepartment of Sports Medicine, Leicester General Hospital, Leicester MRI findings in three cases of ganglion cyst of the common peroneal nerve are presented. In each case the cyst was imaged as an oval structure in transverse section adjacent to the fibular neck. The cyst extended in a tubular fashion over several slices with an inferior extension towards the superior tibiofibular joint. Signal intensity was intermediate on T1- and high on T2-weighted images. In addition, increased signal on both T1- and T2-weighted images was noted throughout the peroneal compartment and was associated with clinical and EMG evidence of denervation. This has not been previously described but may be an important indirect sign which, when seen, should prompt a careful search in the region of the fibular neck for an underlying ganglion cyst of the common peroneal nerve. Coakley, F.V., Finlay, D.B., H a r p e r , W . M . & Allen, M.J. (1995). Clinical Radiology 50, 168-169. Direct a n d Indirect M R I F i n d i n g s in G a n g l i o n Cysts o f the C o m m o n P e r o n e a l Nerve
Accepted for Publication 2 November 1994 T h e c o m m o n p e r o n e a l (fibular or lateral popliteal) nerve arises as a b r a n c h o f the sciatic nerve in the apex o f the popliteal fossa. It passes inferolaterally, medial to biceps femoris, a n d then winds laterally a r o u n d the head o f the fibula before dividing into deep a n d superficial b r a n c h e s which supply the p e r o n e a l c o m p a r t m e n t in the leg. A few small articular b r a n c h e s supply the superior tibiofibular j o i n t . G a n g l i o n cysts at the knee in the nerve are rare b u t well recognized entities [1]. They typically arise in close p r o x i m i t y to the neck o f the fibula [2]. P r e s e n t a t i o n is with pain, paraesthesia o r weakness in the territory o f the c o m m o n p e r o n e a l nerve. This clinical c o m b i n a t i o n is said to be diagnostic, whether or n o t there is a p a l p a b l e swelling at the fibular neck [3]. There has been one previous report describing the M R I findings o f p e r o n e a l nerve e n t r a p m e n t due to a g a n g l i o n cyst [4]. Three f u r t h e r cases are presented here. I n each, the cyst was imaged as t u b u l a r structure a d j a c e n t to the fibular neck. I n a d d i t i o n , in each case there was increased signal t h r o u g h o u t the p e r o n e a l c o m p a r t m e n t associated with d e n e r v a t i o n . This indirect finding m a y be a n i m p o r t a n t clue to the presence o f a n u n d e r l y i n g g a n g l i o n cyst. CASE REPORTS
Case 2. A 34-year-old man presented with a 3 month history of episodic pain in the anterior aspect of the left shin and a 1 week history of left foot drop. On examination there were signs of a common peroneal nerve palsy. EMG showed complete denervation in the deep branch of the common peroneal nerve. MRI findings were essentially the same as those in Case 1. At operation a large intraneural ganglion was found. It appeared to arise from the superior tibiofibular joint and to entwine amongst the fibres of the common peroneal nerve. Histological examination confirmed the diagnosis of a ganglion cyst. There was partial resolution of the patient's foot drop postoperatively. Case 3. A 61-year-old woman presented with an 8 month history of right foot drop associated with episodic pain in the right shin. On examination there were signs of a common peroneal nerve palsy and a palpable swellingat the fibular neck. Paraesthesia could be provoked by tapping this swelling. EMG showed a severe common peroneal nerve lesion. MRI findings were essentially the same as those in Case 1. At surgery a swelling was found in the deep branch of the common peroneal nerve and could not be separated from it. A 6 cm section of nerve was resected. Histology showed an intraneural ganglion cyst. The patient was left with a permanent foot drop.
DISCUSSION These cases illustrate the ease with which M R I images g a n g l i o n cysts of the c o m m o n p e r o n e a l nerve. The finding of a t u b u l a r structure n e a r the fibular neck extending l o n g i t u d i n a l l y over several slices with a n inferior exten-
Case 1. A 16-year-oldmale presented with a 4 week history of pain around the right knee and a 1 week history of right foot drop. On examination there were signs of a common peroneal nerve palsy. EMG showed evidence of severe but partial denervation on the common peroneal nerve territory. MRI showed a mass in close proximity to the neck of the fibula extending in a tubular fashion over several slicesand with intermediate T1 and high T2 signal intensity. There was a small inferior extension of the mass towards the superior tibiofibular joint (Figs 1 and 2). There was also increased signal throughout the peroneal compartment on both T1- and T2-weightedimages (Fig. 3). At surgery, a ganglion was found at the neck of the fibula and this was felt to be related to the superior tibiofibular joint (Fig. 4). The ganglion was dissected free and histologicalexamination confirmedthe diagnosis of a ganglion cyst. Follow-up at 4 weeks postoperatively showed the foot drop to be improving significantly. Correspondence to: Dr Fergus Coakley, Senior Registrar in Radiology, Leicester Royal Infirmary, Leicester LE1 5WW.
Fig. 1-Tl-weighted (2000/20) transverse MR images at a level just below the knee. The ganglion cyst is seen as an oval mass of intermediate signal intensity near the right fibular neck (arrowhead).
GANGLIONCYSTSOF COMMONPERONEALNERVE
169
Fig. 2 T2-weightedimage (2000/80) at the same levelas Fig. 1 showing the high signal from the cyst (arrowhead) with a small anterior extension towards the superior tibiofibularjoint. Fig. 4 lntraoperative photograph of the ganglion cyst imaged in Figs 1 3. A normal section of the common peroneal nerve is seen supported by a tape. Distally the nerve is expanded by the ganglion cyst (arrowhead).
Fig. 3-T2-weighted image (2000/80) at mid-calf level showing increased signal throughout the right peroneal compartment (arrowhead). This change is also evident, though less obvious, in Figs 1 and 2.
sion towards the superior tibiofibular joint and with intermediate T I and high T2 signal intensity was characteristic. The T 1 signal may appear higher than expected for a fluid-filled structure. This is probably because these cysts contain a mucoid glue-like material [2,5] rather than simple watery fluid. These M R I findings could conceivably suggest a venous structure; however, the confinement to a small number of contiguous slices together with t h e absence of a vein at this site normally should help in making the distinction. In addition, scanning both knees to allow comparison m a y be helpful. The finding of increased signal in the peroneal compartment in association with clinical and E M G evidence of denervation is noteworthy and has not been previously reported with ganglion cysts o f the c o m m o n peroneal nerve. Denervation is a well described [6,7] cause of such change in the M R signal from muscle, though perhaps not widely recognized. It is related to shrinkage of the denervated muscle cells with a compensatory increase in the extracellular fluid volume and perhaps also to fatty infiltration [7]. This finding was the most prominent sign, albeit indirect, in the three cases described. The finding of increased signal in the peroneal c o m p a r t m e n t should p r o m p t careful scrutiny of the region o f the fibular neck for an underlying ganglion cyst, particularly in the appropriate clinical setting. High signal intensity of skeletal muscle on T2-weighted images is also seen in inflammatory myopathies, exercise-induced change, rhabdomyolysis, c o m p a r t m e n t syndrome and muscle involvement by tumours [7]. A b n o r m a l signal intensity confined to the area supplied by a nerve and E M G findings should help differentiate these conditions from denervation, as in these three cases.
The origin of ganglion cysts found in the common peroneal nerve is controversial. The synovial theory, with which there is currently the most consensus [1], regards these lesions as genuine cysts of articular or paraarticular origin. The finding of a peduncle connecting the cyst to the superior tibiofibular joint is said to be an important point in favour of this theory [8] and in a recent review was seen in 40% of reported cases [1]. The inferior extension of the cyst towards the superior tibiofibular joint seen in all three cases described here would appear to favour this theory. This extension, if seen, is of surgical significance since it has been recommended that the cystic peduncle should preferably be removed to prevent recurrence [1]. It should be noted that while ganglion cysts contain fluid which is very similar to synovial fluid, they are not lined by synovium and do not communicate with the joint cavity [9]. These two features distinguish ganglia from synovial cysts such as Baker's cysts and the terms should not be used interchangeably in order to avoid confusion between true ganglia and synovial cysts related to joints or tendon sheaths. Unfortunately the usage o f the terms as synonyms is frequent in the literature [1,3,8]. REFERENCES
1 Nucci F, Artico M, Santora Aet al. Intraneural synovialcyst of the peroneal nerve: report of two cases and a review of the literature.
Neurosurgery 1990;26:339-344. 2 Gambari PI, Giuliani G, Poppi Met al. Ganglionic cysts of the peroneal nerve at the knee: CT and surgical correlation. Journal of Computer Assisted Tomography 1990;14(5):801-803. 3 Lagarrique J, Robert R, Resche F et al. Kystes synoviaux intranerveux du sciatique poplite externe. Neurochirurgie 1982;28:131-134. 4 Leon J, Marano G. MRI of peroneal nerve entrapment due to a ganglion cyst. Magnetic Resonance Imaging 1987;5:307-309. 5 LeijtenFS, Willen-Frans A, Puylaert JB. Ultrasound diagnosisof an intraneural ganglion of the peroneal nerve. Journal of Neurosurgery 1992;76:538-543. 6 Shabas D, Gerard G, Rossi D. Magnetic resonance imaging examination of denervated muscle. Computed Radiology 1987;11(1):9-13. 7 Uetani M, Hayashi K, Matsunaga N e t aL Denervated skeletal muscle: MR imaging. Radiology 1993;189(2):511-515. 6 Robert R, Resche F, Lajat U et al. Kyste synovial intraneural du sciatique poplite externe. Apropos d'un case. Neurochirurgie 1980;26:135-143. 9 Lichtenstein L. Tumors of synovial joints, bursae, and tendon sheaths. Cancer 1955;8:816-830.