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Occult Isolated Articular Branch Cyst of the Lateral Plantar Nerve
The Journal of Foot & Ankle Surgery 56 (2017) 78–81
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Occult Isolated Articular Branch Cyst of the Lateral Plantar Nerve Nikhil Prasad, MD 1, Kimberly K. Amrami, MD 2, Kivanc Yangi, MD 3, Robert J. Spinner, MD 4 1
Research Fellow, Department of Neurologic Surgery, Mayo Clinic, Rochester, MN Professor, Department of Neurologic Surgery and Radiology, Mayo Clinic, Rochester, MN 3 Research Assistant, Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 4 Professor and Chair, Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 2
a r t i c l e i n f o
a b s t r a c t
Level of clinical Evidence: 4
We present the first known case of cyst fluid localized to an articular branch without involvement of the larger parent nerve. During a routine tarsal tunnel decompression in a patient with fluctuating plantar foot symptoms and “normal” magnetic resonance imaging findings, we identified cyst fluid within an articular branch of the lateral plantar nerve to the subtalar joint. Our incidental intraoperative discovery was corroborated by retrospective review of the magnetic resonance images. Although we do not know whether this cyst was responsible for the patient’s complaints, we believe this finding represents a snapshot into the life cycle of intraneural ganglion cysts: either the “birth” of an ultra-early one or the remnant of a once larger one. Both interpretations are consistent with the unifying articular theory and add further insight into the dynamic phases of the progression of intraneural ganglion cysts. Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: intraneural ganglion cyst lateral plantar nerve tibial nerve
Intraneural ganglion cysts (IGCs) are mucinous cysts found within peripheral nerves. The most common site of occurrence is the peroneal nerve, but other locations include the suprascapular, median, ulnar, radial, tibial, and sciatic nerves. A recent systematic review revealed >50 cases of IGCs arising in the foot and ankle region (1). For 2 centuries, their etiology has been subject to speculation. During the past decade, a significant weight of evidence has pointed toward a dynamic mechanical process, with pressure fluxes in the joints transmitted proximally from the articular branches to the parent nerves, allowing joint fluid to escape through a capsular defect (2). With the experience gained at our institution and evidence from published case reports, we believe that IGCs follow a predetermined path of progression that can be categorized into radiologic phases (2– 4). Pressure on the nerve fascicles can produce neuropathic pain and motor and sensory deficits. IGCs have obvious macroscopic features on imaging (magnetic resonance imaging [MRI] or ultrasonography) and during surgery; however, it is not uncommon, owing to limitations in imaging facilities, or radiologist or surgeon experience with this rare condition, for IGCs to be confused with extraneural ganglion cysts. Failure to identify the joint–ganglion connection can be associated with a high rate of recurrence (5).
Address correspondence to: Robert J. Spinner, MD, Department of Neurologic Surgery, Mayo Clinic, Gonda 8-214, Rochester, MN 55905. E-mail address: [email protected] (R.J. Spinner).
During the course of a recent routine tarsal tunnel decompression, we made the incidental discovery of a tiny amount of cyst fluid in an articular branch to the subtalar joint; no cystic expansion of any parent nerves in the ankle was present. Retrospectively, we could confirm the cyst and its joint connection from the MRI studies. We present this case as the first example of an IGC localized to an articular branch.
Case Report A 46-year-old female presented in April 2011 with a 9-month history of left medial ankle and hindfoot pain, stabbing in nature, with associated paresthesia radiating along the plantar foot. Tinel’s sign was mildly positive at the tarsal tunneldreplicating the pattern of her complaint. Nerve conduction studies (tibial and lateral and medial plantar nerves) demonstrated normal latencies. Electromyography revealed large motor unit potentials in the foot muscles (left first dorsal interossei and abductor digiti minimi). These could have been consistent with either tarsal tunnel syndrome or an early lengthdependent neuropathy. The findings from both MRI and computed tomography were unremarkable. The patient’s symptoms, although fluctuating in severity, had persisted for several weeks and had responded only transiently to a tarsal tunnel block. With the patient in the supine position, under general anesthesia, tarsal and plantar tunnel decompression was performed, including neurolysis of the medial and lateral plantar and medial calcaneal
1067-2516/$ - see front matter Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2016.09.008
N. Prasad et al. / The Journal of Foot & Ankle Surgery 56 (2017) 78–81
79
Fig. 1. (A) Intraoperative photograph demonstrating divergence of the tibial nerve (TN) into the medial plantar (MPN), lateral plantar (LPN), and medial calcaneal (MCN) nerves. (B) A magnified view of the cystic-appearing articular branch of the LPN (arrowhead).
nerves. Joint fluid was noted in the operative field but the source could not be identified. A thorough inspection revealed a cystic articular branch, from the lateral plantar nerve (Fig. 1), to the subtalar joint. This branch was resected. Histologic examination confirmed the specimen to be of neuronal origin, with no cyst capsule identified. The postoperative course was unremarkable, and the patient had complete relief of the medial forefoot, hindfoot, and plantar pain at the 3-month and 5-year (August 2016) follow-up visits. Reinterpretation of the MRI studies demonstrated a small amount of cyst in the lateral plantar nerve at the subtalar joint (Fig. 2). Discussion To our knowledge, this is the first case that demonstrates a tiny volume of joint fluid, isolated within an articular branch, without involvement of the parent nerve. The small size of the collection precluded diagnosis on the initial review of the radiologic imaging studies, and it could easily have been missed during the operation. On retrospective review of the MRI scans, we identified a subtle indication of the small fluid globule seen during surgery, which was
confirmed to be in the lateral plantar nerve, articulating with the subtalar joint. In this case, the tiny amount of cyst material within the articular branch and its origin from the subtalar joint were easily seen owing to the use of multiplanar imaging and a high-resolution, 3T technique. The small amount of cyst material and its association with the nerve could have been easily overlooked on an examination with less attention to technique. We believe that the present case represents the earliest component of proximal propagation of an intraneural ganglion: fluid within the articular branch but not extending to the parent nerve. The subtalar joint is innervated by branches from the sural, tibial, and medial plantar nerves (6); however, cadaveric studies have also demonstrated an occasional supply from the lateral plantar nerve (7–9). A systematic review of the published data revealed 12 cases of medial plantar IGCs (1). Two cases of primary lateral plantar nerve IGC have been reported, both of which had subtalar joint connections (10,11). These reports, and knowledge of the anatomic variation in the nerve supply to the ankle region, corroborate our finding of joint fluid within an articular branch of the lateral plantar nerve. Histopathologic examination did not reveal any evidence of cyst wall formation,
Fig. 2. (A) Coronal T2-weighted magnetic resonance image with fat suppression showing the intraneural cyst within the articular branch of the lateral plantar nerve that arose from the medial subtalar joint (arrow). (B) Axial T2-weighted magnetic resonance image with fat suppression showing the cyst within the lateral plantar nerve (arrow). (C) Axial proton density magnetic resonance image without fat suppression showing the cyst within the lateral plantar nerve (arrow) and the normal medial plantar branch (arrowhead).
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N. Prasad et al. / The Journal of Foot & Ankle Surgery 56 (2017) 78–81
synovial cuboid cells, or fibroblast proliferation, which have previously been associated with intraneural cyst proliferation (12). The articular branch specimen was merely noted to be neural in origin, with no other significant findings. It is quite understandable that this small amount of cyst material did not leave any discrete pathologic signs. Recently, our group has characterized the propagation pattern of a medial plantar IGC, which had ascended (phase I) to the tibial nerve, where it crossed over (phase II) and then descended (phase III) down the medial and lateral plantar nerves (13). Based on a previous
description of the stages of ascent (phase I) in the prototype, the peroneal IGC derived from the superior tibiofibular joint (14), we can analogously subdivide cyst propagation of (medial or lateral) plantar intraneural cysts into stages (Fig. 3): from the (subtalar) joint (stage 0), to the articular branch (stage 1), a plantar nerve (stage 2), and the tibial nerve (stage 3). Conclusions about cyst propagation cannot be definitively made without serial imaging studies. It is possible that given the dynamic nature of IGCs (2), that this occult “micro-cyst” (measuring <1 mm in diameter) could have represented the earliest phase of a larger cyst or,
Fig. 3. Illustration showing the anatomy and pathoanatomy of a lateral plantar intraneural ganglion cyst arising from the subtalar joint. The stages of ascent (phase I) of intraneural ganglion cyst propagation are illustrated. Two possible explanations for the occult cyst localized to the articular branch are illustrated: an early “micro-cyst” (i.e., the first sign of intraneural ganglion cyst progression along the nerve) or a late sign of spontaneous cyst resorption due to variations in intracapsular pressure. (By permission of Mayo Foundation for Medical Education and Research. All rights reserved.)
N. Prasad et al. / The Journal of Foot & Ankle Surgery 56 (2017) 78–81
alternatively, could have been a residual cyst (i.e., the late phase of a resorbed intraneural cyst; Fig. 3). At a different time, the cyst could have propagated proximally to the tibial nerve or produced local changes, such as mass effect within the tarsal tunnel. However, it is impossible to know whether the “occult” cyst identified in the present case was an incidental finding or was responsible for the clinical symptoms. Still, our case potentially provides a snapshot that will allows us to further characterize the pathoanatomic mechanisms responsible for what remains a rare and poorly understood disease process. In conclusion, we have presented a novel example of cyst fluid localized to the articular branch of the lateral plantar nerve. It is unknown whether the occult cyst represented an ultra-early phase of a cyst that had not yet formed or the remnant of one that had been larger and involved the parent nerve before being nearly completely resorbed. In either case, this isolated articular branch involvement is the conduit for IGC progression and can easily be overlooked.
3. 4.
5.
6.
7. 8.
9. 10. 11.
References 1. Desy NM, Wang H, Elshiekh MAI, Tanaka S, Choi TW, Howe BM, Spinner RJ. Intraneural ganglion cysts: a systematic review and reinterpretation of the world’s literature. J Neurosurg 125:615–630, 2016. 2. Spinner RJ, Amrami KK, Wolanskyj AP, Desy NM, Wang H, Benarroch EE, Skinner JA, Rock MG, Schiethauer BW. Dynamic phases of peroneal and tibial
12. 13.
14.
81
intraneural ganglia formation: a new dimension added to the unifying articular theory. J Neurosurg 107:296–307, 2007. Spinner RJ, Carmichael SW, Wang H, Parisi TJ, Skinner JA, Amrami KK. Patterns of intraneural ganglion cyst descent. Clin Anat 21:233–245, 2008. Colombo EV, Howe BM, Amrami KK, Spinner RJ. Elaborating upon the descent phase of fibular and tibial intraneural ganglion cysts after cross-over in the sciatic nerve. Clin Anat 27:1133–1136, 2014. Desy NM, Lipinski LJ, Tanaka S, Amrami KK, Rock MG, Spinner RJ. Recurrent intraneural ganglion cysts: pathoanatomic patterns and treatment implications. Clin Anat 28:1058–1069, 2015. Sarrafian SK, Kelikian AS. Nerves. In: Sarrafian’s Anatomy of the Foot and Ankle: Descriptive, Topographical, Functional, ed 3, pp. 423–426, edited by AS Kelikian, Wolters Kluwer Health/Lippincott Williams & Wilkins, Philadelphia, 2011. Champetier J. Innervation of the tibiotarsal joint (articulation talocruralis). Acta Anat 77:398–421, 1970. Mentzel M, Fleischmann W, Bauer G, Kinzl L. Ankle joint denervation. Part 1: anatomydthe sensory innervation of the ankle joint. Foot Ankle Surg 5:15–20, 1999. Moore KL, Dalley AF II, Agur AMR. Clinically Oriented Anatomy, ed 7, Wolters Kluwer Health/Lippincott Williams & Wilkins, Philadelphia, 2013. Choi J, Kim K, Kwak J, Park H, Lee S. Intraneural ganglion cyst in foot and ankle. Korean Foot Ankle Soc 15:223–231, 2011. Davis GA, Cox IH. Tibial intraneural ganglia at the ankle and knee: incorporating the unified (articular) theory in adults and children. J Neurosurg 114:236–239, 2011. Scherman BM, Bilbao JM, Hudson AR, Briggs SJ. Intraneural ganglion: a case report with electron microscopic observations. Neurosurgery 8:487–490, 1981. Isaacs AM, Midha R, Desy NM, Amrami KK, Spinner RJ. The mechanism underlying combined medial and lateral plantar and tibial intraneural ganglia in the tarsal tunnel. Acta Neurochir (Wien) 158:2225–2229, 2016. Spinner RJ, Atkinson JL, Tiel RJ. Peroneal intraneural ganglia: the importance of the articular branch: a unifying theory. J Neurosurg 99:330–343, 2003.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Occult Isolated Articular Branch Cyst of the Lateral Plantar Nerve Nikhil Prasad, MD 1, Kimberly K. Amrami, MD 2, Kivanc Yangi, MD 3, Robert J. Spinner, MD 4 1
Research Fellow, Department of Neurologic Surgery, Mayo Clinic, Rochester, MN Professor, Department of Neurologic Surgery and Radiology, Mayo Clinic, Rochester, MN 3 Research Assistant, Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 4 Professor and Chair, Department of Neurologic Surgery, Mayo Clinic, Rochester, MN 2
a r t i c l e i n f o
a b s t r a c t
Level of clinical Evidence: 4
We present the first known case of cyst fluid localized to an articular branch without involvement of the larger parent nerve. During a routine tarsal tunnel decompression in a patient with fluctuating plantar foot symptoms and “normal” magnetic resonance imaging findings, we identified cyst fluid within an articular branch of the lateral plantar nerve to the subtalar joint. Our incidental intraoperative discovery was corroborated by retrospective review of the magnetic resonance images. Although we do not know whether this cyst was responsible for the patient’s complaints, we believe this finding represents a snapshot into the life cycle of intraneural ganglion cysts: either the “birth” of an ultra-early one or the remnant of a once larger one. Both interpretations are consistent with the unifying articular theory and add further insight into the dynamic phases of the progression of intraneural ganglion cysts. Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: intraneural ganglion cyst lateral plantar nerve tibial nerve
Intraneural ganglion cysts (IGCs) are mucinous cysts found within peripheral nerves. The most common site of occurrence is the peroneal nerve, but other locations include the suprascapular, median, ulnar, radial, tibial, and sciatic nerves. A recent systematic review revealed >50 cases of IGCs arising in the foot and ankle region (1). For 2 centuries, their etiology has been subject to speculation. During the past decade, a significant weight of evidence has pointed toward a dynamic mechanical process, with pressure fluxes in the joints transmitted proximally from the articular branches to the parent nerves, allowing joint fluid to escape through a capsular defect (2). With the experience gained at our institution and evidence from published case reports, we believe that IGCs follow a predetermined path of progression that can be categorized into radiologic phases (2– 4). Pressure on the nerve fascicles can produce neuropathic pain and motor and sensory deficits. IGCs have obvious macroscopic features on imaging (magnetic resonance imaging [MRI] or ultrasonography) and during surgery; however, it is not uncommon, owing to limitations in imaging facilities, or radiologist or surgeon experience with this rare condition, for IGCs to be confused with extraneural ganglion cysts. Failure to identify the joint–ganglion connection can be associated with a high rate of recurrence (5).
Address correspondence to: Robert J. Spinner, MD, Department of Neurologic Surgery, Mayo Clinic, Gonda 8-214, Rochester, MN 55905. E-mail address: [email protected] (R.J. Spinner).
During the course of a recent routine tarsal tunnel decompression, we made the incidental discovery of a tiny amount of cyst fluid in an articular branch to the subtalar joint; no cystic expansion of any parent nerves in the ankle was present. Retrospectively, we could confirm the cyst and its joint connection from the MRI studies. We present this case as the first example of an IGC localized to an articular branch.
Case Report A 46-year-old female presented in April 2011 with a 9-month history of left medial ankle and hindfoot pain, stabbing in nature, with associated paresthesia radiating along the plantar foot. Tinel’s sign was mildly positive at the tarsal tunneldreplicating the pattern of her complaint. Nerve conduction studies (tibial and lateral and medial plantar nerves) demonstrated normal latencies. Electromyography revealed large motor unit potentials in the foot muscles (left first dorsal interossei and abductor digiti minimi). These could have been consistent with either tarsal tunnel syndrome or an early lengthdependent neuropathy. The findings from both MRI and computed tomography were unremarkable. The patient’s symptoms, although fluctuating in severity, had persisted for several weeks and had responded only transiently to a tarsal tunnel block. With the patient in the supine position, under general anesthesia, tarsal and plantar tunnel decompression was performed, including neurolysis of the medial and lateral plantar and medial calcaneal
1067-2516/$ - see front matter Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2016.09.008
N. Prasad et al. / The Journal of Foot & Ankle Surgery 56 (2017) 78–81
79
Fig. 1. (A) Intraoperative photograph demonstrating divergence of the tibial nerve (TN) into the medial plantar (MPN), lateral plantar (LPN), and medial calcaneal (MCN) nerves. (B) A magnified view of the cystic-appearing articular branch of the LPN (arrowhead).
nerves. Joint fluid was noted in the operative field but the source could not be identified. A thorough inspection revealed a cystic articular branch, from the lateral plantar nerve (Fig. 1), to the subtalar joint. This branch was resected. Histologic examination confirmed the specimen to be of neuronal origin, with no cyst capsule identified. The postoperative course was unremarkable, and the patient had complete relief of the medial forefoot, hindfoot, and plantar pain at the 3-month and 5-year (August 2016) follow-up visits. Reinterpretation of the MRI studies demonstrated a small amount of cyst in the lateral plantar nerve at the subtalar joint (Fig. 2). Discussion To our knowledge, this is the first case that demonstrates a tiny volume of joint fluid, isolated within an articular branch, without involvement of the parent nerve. The small size of the collection precluded diagnosis on the initial review of the radiologic imaging studies, and it could easily have been missed during the operation. On retrospective review of the MRI scans, we identified a subtle indication of the small fluid globule seen during surgery, which was
confirmed to be in the lateral plantar nerve, articulating with the subtalar joint. In this case, the tiny amount of cyst material within the articular branch and its origin from the subtalar joint were easily seen owing to the use of multiplanar imaging and a high-resolution, 3T technique. The small amount of cyst material and its association with the nerve could have been easily overlooked on an examination with less attention to technique. We believe that the present case represents the earliest component of proximal propagation of an intraneural ganglion: fluid within the articular branch but not extending to the parent nerve. The subtalar joint is innervated by branches from the sural, tibial, and medial plantar nerves (6); however, cadaveric studies have also demonstrated an occasional supply from the lateral plantar nerve (7–9). A systematic review of the published data revealed 12 cases of medial plantar IGCs (1). Two cases of primary lateral plantar nerve IGC have been reported, both of which had subtalar joint connections (10,11). These reports, and knowledge of the anatomic variation in the nerve supply to the ankle region, corroborate our finding of joint fluid within an articular branch of the lateral plantar nerve. Histopathologic examination did not reveal any evidence of cyst wall formation,
Fig. 2. (A) Coronal T2-weighted magnetic resonance image with fat suppression showing the intraneural cyst within the articular branch of the lateral plantar nerve that arose from the medial subtalar joint (arrow). (B) Axial T2-weighted magnetic resonance image with fat suppression showing the cyst within the lateral plantar nerve (arrow). (C) Axial proton density magnetic resonance image without fat suppression showing the cyst within the lateral plantar nerve (arrow) and the normal medial plantar branch (arrowhead).
80
N. Prasad et al. / The Journal of Foot & Ankle Surgery 56 (2017) 78–81
synovial cuboid cells, or fibroblast proliferation, which have previously been associated with intraneural cyst proliferation (12). The articular branch specimen was merely noted to be neural in origin, with no other significant findings. It is quite understandable that this small amount of cyst material did not leave any discrete pathologic signs. Recently, our group has characterized the propagation pattern of a medial plantar IGC, which had ascended (phase I) to the tibial nerve, where it crossed over (phase II) and then descended (phase III) down the medial and lateral plantar nerves (13). Based on a previous
description of the stages of ascent (phase I) in the prototype, the peroneal IGC derived from the superior tibiofibular joint (14), we can analogously subdivide cyst propagation of (medial or lateral) plantar intraneural cysts into stages (Fig. 3): from the (subtalar) joint (stage 0), to the articular branch (stage 1), a plantar nerve (stage 2), and the tibial nerve (stage 3). Conclusions about cyst propagation cannot be definitively made without serial imaging studies. It is possible that given the dynamic nature of IGCs (2), that this occult “micro-cyst” (measuring <1 mm in diameter) could have represented the earliest phase of a larger cyst or,
Fig. 3. Illustration showing the anatomy and pathoanatomy of a lateral plantar intraneural ganglion cyst arising from the subtalar joint. The stages of ascent (phase I) of intraneural ganglion cyst propagation are illustrated. Two possible explanations for the occult cyst localized to the articular branch are illustrated: an early “micro-cyst” (i.e., the first sign of intraneural ganglion cyst progression along the nerve) or a late sign of spontaneous cyst resorption due to variations in intracapsular pressure. (By permission of Mayo Foundation for Medical Education and Research. All rights reserved.)
N. Prasad et al. / The Journal of Foot & Ankle Surgery 56 (2017) 78–81
alternatively, could have been a residual cyst (i.e., the late phase of a resorbed intraneural cyst; Fig. 3). At a different time, the cyst could have propagated proximally to the tibial nerve or produced local changes, such as mass effect within the tarsal tunnel. However, it is impossible to know whether the “occult” cyst identified in the present case was an incidental finding or was responsible for the clinical symptoms. Still, our case potentially provides a snapshot that will allows us to further characterize the pathoanatomic mechanisms responsible for what remains a rare and poorly understood disease process. In conclusion, we have presented a novel example of cyst fluid localized to the articular branch of the lateral plantar nerve. It is unknown whether the occult cyst represented an ultra-early phase of a cyst that had not yet formed or the remnant of one that had been larger and involved the parent nerve before being nearly completely resorbed. In either case, this isolated articular branch involvement is the conduit for IGC progression and can easily be overlooked.
3. 4.
5.
6.
7. 8.
9. 10. 11.
References 1. Desy NM, Wang H, Elshiekh MAI, Tanaka S, Choi TW, Howe BM, Spinner RJ. Intraneural ganglion cysts: a systematic review and reinterpretation of the world’s literature. J Neurosurg 125:615–630, 2016. 2. Spinner RJ, Amrami KK, Wolanskyj AP, Desy NM, Wang H, Benarroch EE, Skinner JA, Rock MG, Schiethauer BW. Dynamic phases of peroneal and tibial
12. 13.
14.
81
intraneural ganglia formation: a new dimension added to the unifying articular theory. J Neurosurg 107:296–307, 2007. Spinner RJ, Carmichael SW, Wang H, Parisi TJ, Skinner JA, Amrami KK. Patterns of intraneural ganglion cyst descent. Clin Anat 21:233–245, 2008. Colombo EV, Howe BM, Amrami KK, Spinner RJ. Elaborating upon the descent phase of fibular and tibial intraneural ganglion cysts after cross-over in the sciatic nerve. Clin Anat 27:1133–1136, 2014. Desy NM, Lipinski LJ, Tanaka S, Amrami KK, Rock MG, Spinner RJ. Recurrent intraneural ganglion cysts: pathoanatomic patterns and treatment implications. Clin Anat 28:1058–1069, 2015. Sarrafian SK, Kelikian AS. Nerves. In: Sarrafian’s Anatomy of the Foot and Ankle: Descriptive, Topographical, Functional, ed 3, pp. 423–426, edited by AS Kelikian, Wolters Kluwer Health/Lippincott Williams & Wilkins, Philadelphia, 2011. Champetier J. Innervation of the tibiotarsal joint (articulation talocruralis). Acta Anat 77:398–421, 1970. Mentzel M, Fleischmann W, Bauer G, Kinzl L. Ankle joint denervation. Part 1: anatomydthe sensory innervation of the ankle joint. Foot Ankle Surg 5:15–20, 1999. Moore KL, Dalley AF II, Agur AMR. Clinically Oriented Anatomy, ed 7, Wolters Kluwer Health/Lippincott Williams & Wilkins, Philadelphia, 2013. Choi J, Kim K, Kwak J, Park H, Lee S. Intraneural ganglion cyst in foot and ankle. Korean Foot Ankle Soc 15:223–231, 2011. Davis GA, Cox IH. Tibial intraneural ganglia at the ankle and knee: incorporating the unified (articular) theory in adults and children. J Neurosurg 114:236–239, 2011. Scherman BM, Bilbao JM, Hudson AR, Briggs SJ. Intraneural ganglion: a case report with electron microscopic observations. Neurosurgery 8:487–490, 1981. Isaacs AM, Midha R, Desy NM, Amrami KK, Spinner RJ. The mechanism underlying combined medial and lateral plantar and tibial intraneural ganglia in the tarsal tunnel. Acta Neurochir (Wien) 158:2225–2229, 2016. Spinner RJ, Atkinson JL, Tiel RJ. Peroneal intraneural ganglia: the importance of the articular branch: a unifying theory. J Neurosurg 99:330–343, 2003.