MRI of the Achilles tendon-A comprehensive pictorial review. Part one

Abstract

The normal Achilles tendon is composed of twisted subtendons separated by thin high signal septae, which are a potential pitfall on MRI because they mimic a tendon tear. Tendinopathy and full thickness tears may be assessed effectively both on MRI and ultrasound. MRI is superior to ultrasound in detection of partial tears and for postoperative assessment. The use of fat suppression sequences allows the ability to detect focal lesions. Sagittal and coronal sections are useful for assessing the distance between stumps of a ruptured tendon. Sequences with contrast are indicated in postoperative investigations and suspicion of infection, arthritis or tumor. MRI may reveal inflammatory changes with minor symptoms long before the clinical manifestations of seronegative spondyloarthropathy. The most common non-traumatic focal lesion of the Achilles tendon is Achilles tendon xanthoma, which is manifested by intermediate or slightly higher signal on T1- and T2-weighted images compared to that in the normal Achilles tendon. Other tumors of the Achilles tendon are very rare, whereas the involvement of the tendon from tumor in adjacent structures is more frequent. The novel MRI sequences may help to detect disorders of the Achilles tendon more specifically before clinical manifestation. Regeneration or remodeling of the Achilles tendon can be non-invasively detected and monitored in diffusion tensor imaging. Assessment of healing is possible using T2-mapping while evaluating the tendon vascularization in intravoxel incoherent motion MRI.

Keywords: Achilles tendon; Achilles tendon xanthoma; MRI; Spondyloarthropathy; Tendon.

Fig. 1

Normal Achilles tendon. A 32-year-old patient with clinical suspicion of a ganglion. MRI of the ankle (a-d) showed the higher signal within the Achilles tendon (arrows), which corresponds to the loose connective tissue between the subtendons. a - sagittal T2-weighted FS; b and c - axial section PD-weighted; d - coronal section PD FS.

Fig. 2

The plantaris tendon (straight arrow) contributes to the paratenon. A 48-year-old patient with pain in the Achilles tendon. Distally, the plantaris tendon (straight arrow) divides into small parts and merges with the paratenon, mimicking fibrosis on the axial section. The insertion is the calcaneus (straight arrow on figure a). The MRI (PD-weighted) revealed thickening of the Achilles tendon (curved arrow).

Fig. 3

Rupture and infection of the Achilles tendon graft. A 76-year-old patient received a tendon graft because of a chronic Achilles tendon rupture 6 months ago. She had a wound that would not heal, despite treatment with negative pressure wound therapy. Fever and malaise in the past few days and worse function of the reconstructed tendon. MRI (a-f) with contrast was performed. Rupture of the graft with retraction was revealed (straight arrow). Fluid collection with enhanced walls (dashed arrows) around the graft and fistula (curved arrow) is visible. Extensive thickening of the paratenon (*) and adhesions in Kager's fat pad are present. A- T2- weighted with fat suppression, b- T1- weighted with fat suppression and contrast, c- T1- weighted, d, e and f - T1- weighted with fat suppression and contrast.

Fig. 4

Postoperative infection of the Achilles tendon insertion after surgery for Haglund's deformity. Surgery was performed 5 weeks ago. The wound is not healing, and now, there is redness and swelling of the Achilles tendon insertion. Alteration of the structure, loss of fibrillar structure of the tendon with edema, and reactive changes in the subcutaneous tissue are visible (straight arrow); however, it is challenging to distinguish postoperative changes from infections based only on MRI (a-d). The presence of abscess was ruled out after contrast injection (not seen in the figure). A postoperative defect in the calcaneus (curved arrow) and adhesions with alteration in Kager's fat pad are visible. Diffuse bone marrow edema in the calcaneus is present. Screws in the calcaneus (dashed arrow). a- PD-weighted; b and c - PD-weighted with fat suppression; d - T1-weighted.

Fig. 5

Infection of the Achilles tendon because of a non-healing wound on the heel in a 68-year-old patient. MRI (a-d) revealed extensive edema of the skin and subcutaneous tissue (dashed arrow) around the fistula (curved arrow). After contrast administration, enhancement is visible in the Achilles tendon (straight arrow) at the fistula level. A small area of bone marrow edema in the calcaneus (curved dashed arrow) is probably not related to inflammation. A- T1- weighted, b- T1- weighted with contrast, c and d- T1- weighted with fat suppression and contrast.

Fig. 6

A 26-year-old patient with a suspicion of spondylarthritis presenting with discomfort in the insertion of the Achilles tendon. a and c- T2-weighted with fat suppression; b - T2-weighted. MRI revealed retrocalcaneal bursitis (dashed arrow) and bone marrow edema in the Achilles tendon insertion, however no erosions are present. Thickening of the Achilles tendon in midportion is visible (*), however no alteration in the signal of the Achilles tendon was revealed. A-T2- weighted, b- PD- weighted, c- PD-weighted with fat suppression.

Fig. 7

Large soft tissue tumor in the triceps surae muscle (histology showed undifferentiated pleomorphic sarcoma). A 43-year-old patient under treatment for the tumor. The control MRI showed necrosis in the tumor (curved arrow). The aponeuroses of the gastrocnemius and soleus muscles, as well as the Achilles tendon, are dislocated (dashed arrow) because of mass effect. a - PD-weighted; b - T2-weighted.

Fig. 8

A 27-year-old athlete presents with a palpable focal thickening of the medial part of the Achilles tendon. Clinical suspicion of lipoma. MRI revealed a ganglion-like structure on the medial part of the midportion of the Achilles tendon (straight arrow). A similar lesion is visible on the medial side of the insertion (dashed arrow). No contrast enhancement was noticed, and the radiological diagnosis was ganglions. Surgery was performed, and the proximal lesion was removed. The postoperative diagnosis was ganglion. a-e - PD-weighted with fat suppression.

Fig. 9

A 33-year-old patient who presents after suffering a direct injury to the Achilles tendon. There was neither rupture nor tendon dysfunction revealed on clinical examination. The posttraumatic focal swelling was understood as a hematoma. After 2 weeks, when the clinically suspected hematoma did not decrease in size, an MRI was performed. The heterogeneous fluid lesion with a higher amount of protein (a) (straight arrow) is located between the paratenon (curved arrow) and Achilles tendon. a - T1-weighted; b - STIR; c - PD-weighted with fat suppression; d - T2-weighted. An ultrasound-guided puncture was performed, and clear serous fluid was aspirated. e - ultrasound correlation is presented (longitudinal sagittal section, t - Achilles tendon).