Pictorial Essay
Popliteal Artery Entrapment Syndrome: Role of Imaging in the Diagnosis
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Popliteal artery entrapment syndrome is an uncommon entity typically affecting young athletic males who present with symptoms of calf claudication. It is caused by an anomalous relationship of muscle and artery in the popliteal fossa resulting in extrinsic arterial compression. Repetitive insult to the popliteal artery can cause arterial damage and lead to aneurysm, thromboembolism, and arterial thrombosis. This aggressive natural history warrants early diagnosis and treatment. It is an uncommon entity, with an estimated prevalence of 0.16% [1]. Awareness of this entity and a high index of suspicion are important because tailored imaging studies are required to make the diagnosis and plan surgical intervention. Although conventional angiography has been traditionally used to confirm the diagnosis, cross-sectional imaging also has an important role. The objectives of our study were to describe the imaging findings and elucidate the strengths of different modalities.
| Causes |  |
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The anomalous anatomic relationship responsible for compression of the popliteal artery is caused by abnormal embryologic development of the popliteal fossa. The muscle or the artery can be responsible for the abnormal anatomy, and numerous variations can result (Fig. 1A, 1B, 1C, 1D, 1E). It is important to recognize the normal appearance of the popliteal fossa anatomy (Fig. 2). Only fat should surround the popliteal artery and vein. Several authors have proposed different classification systems, most of which are based on the description of the underlying anatomic variant [2–6]. From a practical standpoint, however, the classification systems have limited usefulness. Variations do not always fit into one of the described categories, and the identification of different types does not affect the treatment or prognosis.
 View larger version (87K) | Fig. 1A. —Graphic illustrations show normal anatomy of popliteal fossa and common variants responsible for arterial entrapment. Normal popliteal artery is adjacent to and lateral to medial head of gastrocnemius muscle, which is normally attached just superior to medial femoral condyle. |
 View larger version (86K) | Fig. 1B. —Graphic illustrations show normal anatomy of popliteal fossa and common variants responsible for arterial entrapment. Abnormal embryologic development can result in numerous anomalous popliteal fossa relationships responsible for entrapment. For example, medial head of gastrocnemius muscle may be attached more laterally than is normal. |
 View larger version (88K) | Fig. 1C. —Graphic illustrations show normal anatomy of popliteal fossa and common variants responsible for arterial entrapment. Anomalous muscle band may be responsible for abnormal attachment. |
 View larger version (83K) | Fig. 1D. —Graphic illustrations show normal anatomy of popliteal fossa and common variants responsible for arterial entrapment. Popliteal artery may take abnormal course medial to normally attached medial head of gastrocnemius muscle. |
 View larger version (81K) | Fig. 1E. —Graphic illustrations show normal anatomy of popliteal fossa and common variants responsible for arterial entrapment. Popliteal artery and gastrocnemius muscle are normally positioned, but fibrous band is responsible for entrapment. |
 View larger version (44K) | Fig. 2. —44-year-old man with normal anatomy of right popliteal fossa. Axial T1-weighted image depicts normal anatomic relationship of popliteal vessels and muscles. Only fat should surround popliteal artery and vein. |
| Sonography | |
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Sonographic examination can show arterial compression elicited by maneuvers such as plantar flexion and dorsiflexion of the feet (Fig. 3A, 3B). Although this finding is consistent with the diagnosis of popliteal artery entrapment syndrome, previous studies have shown occlusion in up to 59% of asymptomatic subjects. In those patients, normal anatomy was confirmed on MRI, and the popliteal artery occlusion was at the soleal sling site as a result of compression by the soleus muscle, lateral head of the gastrocnemius muscle, plantaris muscle, and popliteus muscle [7]. Other nonspecific findings that can be seen on sonography include popliteal artery aneurysm and popliteal artery occlusion.
 View larger version (172K) | Fig. 3A. —49-year-old man with right popliteal artery entrapment syndrome. Doppler sonogram of right popliteal fossa with leg in neutral position shows normal triphasic waveform. |
 View larger version (160K) | Fig. 3B. —49-year-old man with right popliteal artery entrapment syndrome. Doppler sonogram obtained with plantar flexion of right foot shows compression of popliteal artery with absence of flow. Dynamic popliteal artery compression elicited by plantar flexion of foot is sonographic finding consistent with, but not diagnostic of, popliteal artery entrapment syndrome. This finding can be seen in healthy asymptomatic subjects. |
Doppler sonography has a limited role in the diagnosis of popliteal artery entrapment syndrome, because the imaging findings with this modality are nonspecific and show only the consequences of the abnormal anatomy. Furthermore, normal findings do not exclude the diagnosis, and in our experience, two of seven affected limbs had normal sonographic findings both in neutral and with stress maneuvers.
| Conventional Angiography | |
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This modality has been long used for the diagnosis of popliteal artery entrapment syndrome. Angiography has a wide spectrum of findings reflecting different stages of this disease (Fig. 4A, 4B, 4C, 4D). A large review of the literature reported occlusion in 36%, deviation in 24%, aneurysm or ectasia in 9%, and dynamic stenosis in 32% [4]. Imaging findings of popliteal artery entrapment syndrome on arteriograms are nonspecific in most cases. Occlusion and aneurysm of the popliteal artery due to popliteal artery entrapment syndrome cannot be differentiated from the more commonly seen arteriosclerotic or degenerative causes. Although the arterial luminal changes with plantar or dorsiflexion of the foot are well shown on conventional angiography (Fig. 5A, 5B), these findings do not enable the underlying cause to be identified (Figs. 6A and 6B).
 View larger version (114K) | Fig. 4A. —Spectrum of angiographic findings encountered in popliteal artery entrapment syndrome. Angiogram of 34-year-old woman shows medial angulation of popliteal artery course (arrow). |
 View larger version (111K) | Fig. 4B. —Spectrum of angiographic findings encountered in popliteal artery entrapment syndrome. Angiogram of 21-year-old man shows nonocclusive acute thrombus of popliteal artery (arrowhead) with embolization to distal tibial vessels. |
 View larger version (97K) | Fig. 4C. —Spectrum of angiographic findings encountered in popliteal artery entrapment syndrome. Angiogram of 34-year-old woman shows occlusion of popliteal artery (arrow). |
 View larger version (108K) | Fig. 4D. —Spectrum of angiographic findings encountered in popliteal artery entrapment syndrome. Angiogram of 37-year-old man shows popliteal artery aneurysm. |
 View larger version (119K) | Fig. 5A. —17-year-old girl with bilateral popliteal artery entrapment syndrome. Conventional angiogram of both lower extremities in neutral position reveals normal findings. |
 View larger version (138K) | Fig. 5B. —17-year-old girl with bilateral popliteal artery entrapment syndrome. However, conventional angiogram of both lower extremities with forced plantar flexion of feet reveals high-grade narrowing of left popliteal artery and occlusion of right popliteal artery. Underlying causative anomaly of bilateral arterial entrapment cannot be detected on conventional angiography. |
 View larger version (99K) | Fig. 6A. —32-year-old woman with popliteal artery entrapment syndrome of left lower extremity who presented with calf claudication. Angiogram of left popliteal artery in neutral position was unremarkable. |
 View larger version (89K) | Fig. 6B. —32-year-old woman with popliteal artery entrapment syndrome of left lower extremity who presented with calf claudication. Angiogram with plantar flexion of left foot shows narrowing (arrow) of left popliteal artery. |
| MRI and MR Angiography | |
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MRI and MR angiography have emerged as promising imaging modalities for the diagnosis of popliteal artery entrapment syndrome. The advantages intrinsic to these modalities (nonionizing radiation, multiplanar capabilities, high soft-tissue contrast, avoidance of iodinated contrast material, and noninvasive nature) and the potential to yield both the physiologic and anatomic information necessary for the diagnosis of popliteal artery entrapment syndrome make these modalities an attractive alternative diagnostic examination (Fig. 7A, 7B). MRI can nicely show the abnormal anatomy responsible for the entrapment (Figs. 6A, 6B, 6C and 8A, 8B, 8C). In addition, the dynamic compression can also be shown with MR angiographic techniques. The abnormal muscle or fibrous slip responsible for entrapment can be prominent or subtle (Fig. 9).
 View larger version (181K) | Fig. 7A. —47-year-old man with right calf claudication who was found to have popliteal artery entrapment syndrome. Two-dimensional time-of-flight MR angiogram shows occlusion (arrow) of right popliteal artery. |
 View larger version (172K) | Fig. 7B. —47-year-old man with right calf claudication who was found to have popliteal artery entrapment syndrome. Axial T1-weighted image reveals underlying cause of occlusion to be abnormal muscle band (arrow) arising from medial head of gastrocnemius muscle. MRI has advantage of showing both arterial changes and underlying abnormality found in patients with popliteal artery entrapment syndrome. |
 View larger version (179K) | Fig. 6C. —32-year-old woman with popliteal artery entrapment syndrome of left lower extremity who presented with calf claudication. Axial T1-weighted image reveals abnormal muscle slip (arrow) between popliteal artery (arrowhead) and popliteal vein responsible for arterial entrapment. Angiography (A and B) does not show underlying cause of arterial abnormalities. |
 View larger version (114K) | Fig. 8A. —44-year-old man with popliteal artery entrapment syndrome in left lower extremity. Axial T1-weighted image reveals abnormal muscle slip (arrow) between popliteal vessels. |
 View larger version (126K) | Fig. 8B. —44-year-old man with popliteal artery entrapment syndrome in left lower extremity. Time-of-flight MR angiogram of popliteal arteries in neutral position shows normal arterial flow. |
 View larger version (95K) | Fig. 8C. —44-year-old man with popliteal artery entrapment syndrome in left lower extremity. Time-of-flight MR angiogram of popliteal arteries with plantar flexion of feet shows near occlusion (arrow) of left popliteal artery and no change in right leg. MRI and MR angiography have potential to show both functional arterial changes and abnormal anatomy responsible for entrapment. |
 View larger version (168K) | Fig. 9. —37-year-old man with popliteal artery entrapment syndrome. Axial T1-weighted image of right popliteal fossa reveals prominent abnormal muscle (arrow) responsible for arterial entrapment. |
| Treatment | |
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The definitive treatment for popliteal artery entrapment syndrome is surgical intervention. Because of the progressive nature of this entity, even asymptomatic limbs should have surgical correction to prevent irreversible change [8]. Early detection and treatment are associated with better long-term results [9]. Decompression with musculotendinous transection is advised in all cases of popliteal entrapment, and if significant degeneration or occlusion of the popliteal artery is present, arterial reconstruction should be performed. If transection of the anomalous muscle is not performed together with the arterial reconstruction, symptoms can recur because of persistent extrinsic compression on the graft (Fig. 10A, 10B, 10C).
 View larger version (120K) | Fig. 10A. —34-year-old woman who previously underwent surgery for popliteal artery entrapment syndrome in right extremity. Gadolinium-enhanced time-of-flight MR angiogram of right lower extremity in neutral position shows widely patent popliteal artery interposition graft (arrowheads). |
 View larger version (110K) | Fig. 10B. —34-year-old woman who previously underwent surgery for popliteal artery entrapment syndrome in right extremity. Gadolinium-enhanced time-of-flight MR angiogram of right lower extremity with plantar flexion reveals occlusion of graft. |
 View larger version (152K) | Fig. 10C. —34-year-old woman who previously underwent surgery for popliteal artery entrapment syndrome in right extremity. Axial T1-weighted image shows intact aberrant muscle slip (arrow) responsible for entrapment. Abnormality must be corrected at surgery to avoid recurrence of symptoms. |
| Summary | |
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Popliteal artery entrapment syndrome is an uncommon entity with a spectrum of findings. Awareness of the imaging findings is impotant to tailor the examination for confirmation of the diagnosis and surgical planning. The diagnosis of popliteal artery entrapment syndrome requires not only depiction of the arterial changes but also identification of the abnormal anatomic structures responsible for the entrapment. Although arterial compression can be shown on conventional angiography or sonography, the underlying anatomic abnormality cannot be identified on either modality. Tailored MRI and MR angiography can show the abnormal muscular or fibrous attachment and the arterial findings necessary for diagnosis and surgical planning.
Address correspondence to T. A. Macedo.
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