Musculoskeletal systemCase Type
Jenifer Rubio Medina, Ángela Fernández López, Elena Lozano Setién, Lorenzo Abad OrtizPatient
81 years, male
An 81-years-old male with a past medical history of prostate cancer in treatment with complete androgenic hormonal block. Actually, diagnosed with rectal cancer. Whole-body CT rejected metastatic disease but CT images demonstrated a probably extra-articular cystic lesion in soft parts adjacent to the posterior region of the left hip.
CT images demonstrated a well-defined extra-articular mass in soft parts adjacent to the posterior region of the left hip, hypodense (probably cystic lesion) with mild bone remodelling of the cortical bone adjacent which suggests a long time of evolution. (Fig.1)
A full hip MRI was performed on a 1.5 Tesla MRI scanner, consisting of T1 and T2-weighted, T2 weighted fat-saturated, STIR and intravenous gadolinium- T1 sequences in coronal and axial plane for further characterization of the lesion.
MRI images of the left hip showed a well-defined and extra-articular mass, surrounding the quadratus femoris tendon, measuring 6 x 7 cm. The mass was hypointense to muscle on T1-weighted images (Fig2) and hyperintense to fat on T2-weighted images with multiple septa (Fig.3). Following intravenous Gd-DTPA administration, the lesion shows inhomogeneous enhancement (Fig.4).
Due patient`s clinical context ultrasound-guided biopsy was required and revealed “myxoid tumour”.
Myxoid tumours of soft tissue are a miscellaneous group of benign and malignant mesenchymal tumours with an abundance of extracellular mucoid material. These lesions may mimic cysts because of the high water content 
Juxta-articular myxoma (JAM) is an uncommon benign mesenchymal neoplasm without malignant potential. The incidence of this lesion is highest in males between their 3rd and 5th decades of life. JAM is most commonly associated with large joints. The most frequent localization is the knee (88% of cases), followed by the elbow and shoulder, rarely ankle and wrist, and less frequently hip. [2, 3]
The causes of JAM are not clear, although post-traumatic or post arthritis disease may play a significant role in the development. 
On ultrasound, the lesion may appear like a complex cystic mass (hypo- or anechoic with increased through-transmission and posterior acoustic enhancement) or may even appear solid. It is hypovascular. The ultrasound image is not specific enough and it does not enable diagnosis. CT typically shows a well-defined homogeneous soft tissue denser than water but less dense than muscle. The most precise examination, which enables diagnosis, is magnetic resonance imaging. A typical image of myxoma in magnetic resonance imaging is a well-defined lesion with fluid-like signal intensity (low signal intensity on T1-weighted images and high signal intensity on T2-weighted images). The presence of central contrast enhancement demonstrated that this was predominantly solid rather than a cystic lesion. [1, 3]
Management options include observation because of its benign behaviour or surgical excision. Postoperative recurrence is seen in approximately 30% of JAMs within five years of excision.
Other types of myxoma are intramuscular, superficial angiomyxoma, cutaneous aggressive angiomyxoma, and myxoid neurothekeoma (myxoma of the nerve sheath). Intramuscular myxoma is the most commonly encountered myxoma in clinical practice, occurring in the thigh, upper arm and buttock, and does not recur after simple excision. Intramuscular myxomas are usually solitary but may be multiple and, in this scenario, are usually associated with monostotic or polyostotic fibrous dysplasia, which is known as Mazabraud’s syndrome. JAM and intramuscular myxoma share the same histological characteristics, but are differentiated by lesion location and the high recurrence rate of JAM 
 Petscavage-Thomas JM, Walker EA, Logie Cl, Clarke LE, Duryea DM, Murphey MD. Soft-tissue myxomatous lesions: review of salient imaging features with pathologic comparison. Radiographics. 2014;34(4):964-80 (PMID: 25019436)
 King DG, Saifuddin A, Preston HV, Hardy GJ, Reeves BF. Magnetic resonance imaging of juxta-articular myxoma. Skeletal Radiol. 1995; 24:145–147 (PMID: 7747183)
 Körver RJ, Theunissen PH, van de Kreeke WT, van der Linde MJ, Heyligers IC. Juxta-articular myxoma of the knee in a 5-year-old boy: a case report and review of the literature (2009:12b). Eur Radiol. 2010;20(3):764–768 (PMID: 20157818)
 Van den Hever, AJ. Juxta-articular myxoma of the wrist. SA Journal of Radiology. 2014;18 (2), 1-5. https://doi.org/10.4102/sajr.v18i2.668
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