DOI: 10.1148/radiol.2453050159
(Radiology 2007;245:916-917.)
© RSNA, 2007
The Celery Stalk Sign1
Panagiota Papadopoulou, MD
1 From the Department of Radiology, AHEPA University Hospital, Thessaloniki, Greece. Received January 31, 2005; revision requested April 1; revision received May 18; final version accepted July 11.
Address correspondence to the author, Troias 10, Kavala, GR – 65403, Greece (e-mail: peggy_pap{at}yahoo.co.uk).
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APPEARANCE
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The celery stalk sign is seen on magnetic resonance (MR) images, especially sagittal T2-weighted images, of the anterior cruciate ligament (ACL), when subtle linear low-signal-intensity fibers course parallel to the long axis of the otherwise hyperintense ligament (Figure) (1–4). The ligament retains its normal orientation (5).
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Figure a: (a) Sagittal T1-weighted MR image (repetition time msec/echo time msec, 520/13) shows mucoid degeneration with enlarged ACL of almost homogeneous intermediate signal intensity, which retains normal orientation. (b) Sagittal intermediate-weighted fat-saturated MR image (3500/42) demonstrates celery stalk sign. High-signal-intensity ACL (arrows) is seen with low-signal-intensity fibers running parallel to its long axis. Erosion of lateral femoral condyle is also evident.
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Figure b: (a) Sagittal T1-weighted MR image (repetition time msec/echo time msec, 520/13) shows mucoid degeneration with enlarged ACL of almost homogeneous intermediate signal intensity, which retains normal orientation. (b) Sagittal intermediate-weighted fat-saturated MR image (3500/42) demonstrates celery stalk sign. High-signal-intensity ACL (arrows) is seen with low-signal-intensity fibers running parallel to its long axis. Erosion of lateral femoral condyle is also evident.
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EXPLANATION
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The normal ACL is composed of collagen fibers and is seen on MR images as a low-signal-intensity band, either as a homogeneous low-signal-intensity strip or as a collection of individual low-signal-intensity fibers (6,7). When mucoid degeneration is present, an amorphous mucoid matrix increases the signal intensity of the ACL and is focally collected between intact, almost parallel fibers (8). This appearance bears similarity to a stalk of celery (5).
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DISCUSSION
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The pathogenesis of mucoid degeneration of the ACL remains unknown. Some theories suggest that it may simply be the result of senescent degeneration, while others suggest that it may evolve from synovial tissue entrapment between ACL fibers, either congenital or acquired (9). Trauma has also been proposed as an etiologic factor (10,11) since it is considered a likely cause of tendon mucoid degeneration (12) and many patients with ACL mucoid degeneration have a history of mild or nonspecific trauma (5,8,11).
Patients may be symptomatic or asymptomatic. Pain is the most common complaint at presentation (5,8). Patients may also be unable to fully flex or extend the knee and may have difficulty in climbing up or down stairs (9,10). The source of pain is unclear and may be either mechanical irritation due to the bulk of the ligament or a chemically mediated reaction (8,13).
On MR images, the criteria for mucoid degeneration include a bulky ligament of increased signal intensity on images obtained with all pulse sequences, with discrete fibers easily distinguished on T2-weighted images but poorly differentiated on T1-weighted and intermediate-weighted images. Degeneration may involve either the posterolateral or anteromedial bundle of the ACL (8,9). Both bundles have to be identified as intact from origin to insertion to exclude the possibility of a partial tear (10). Mucoid degeneration may coexist with ACL ganglia, as well as with intraosseous cysts at the femoral and tibial attachments, most commonly at the tibial insertion (10).
Mucoid degeneration is often mistaken for a chronic or acute interstitial tear at MR imaging (5,9,13). Abnormal signal intensity of the ACL is one of the primary signs of a tear but, unlike tears, in mucoid degeneration there is no discontinuity of the fibers, and secondary signs of a tear are absent (5). The absence of clinical signs and symptoms consistent with instability also helps to avoid misdiagnosis.
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ACKNOWLEDGMENTS
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I thank Ioannis Kalaitzoglou, MD, and Athanasios S. Dimitriadis, MD, PhD, for providing the images and reviewing this article.
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FOOTNOTES
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Author stated no financial relationship to disclose.
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References
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- Harper S. Case of the month: ACL synovial inflammatory pseudomass. ProScan Imaging Web site. http://www.proscan.com/fw/main/May_2004_to_print-304.html. Published May 2004. Accessed January 26, 2005.
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- Feller JF. MRI of the knee update. Streaming Lectures Education Center: Advanced MRI–from head to toe Web site. http://mri.cpson.com/pdf/MRI_of_the_Knee_Update.pdf. Published 2002. Accessed January 26, 2005.
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