Keywords
myxoma - spine - intramuscular - report
Palavras-chave
mixoma - coluna vertebral - intramuscular - relato
Introduction
Myxoma is a tumor of mesenchymal origin with a slow-growing behavior and an unknown etiology, occurring in a variety of locations. The striated muscle is a rare site (i.e., intramuscular myxoma [IM]), with an estimated incidence of 0,1 to 0,13 per 100.000 individuals.[1] Adults at 40–70 years of age are most affected, with a female predominance.[2] No race predilection nor hereditary pattern were identified.[3] This paper describes the first case of an intramuscular myxoma of the lumbosacral paraspinal muscle in a Brazilian population. The patient provided written consent.
Case History
A 38-year-old woman arrived at our outpatient clinic complaining of increased volume and pain in the right lumbosacral paraspinal region for two months without radiculopathy and with no focal neurological deficits. Past medical history included bariatric surgery nine years before. The physical examination showed a massive, hardened tumor, painless to palpation. A CT scan showed a hypodense formation in the right paraspinal region remodeling of the adjacent bonny structures with no sign of bone infiltration ([Fig. 1]). An MRI showed a cystic-like lesion in the right paraspinal musculature topography, hypointense on T1 sequence and hyperintense on T2, exhibiting fine internal septations of regular contours and well-defined limits, exerting mass effect. It extended from the disc level L2-L3 to the height of the second sacral segment (S2), measuring ∼12,2 × 6,6 × 6,0 cm ([Fig. 1]). A posterior approach was performed with a paramedian incision, dissecting the layers by planes with visualization of a large tumor and a small portion insinuating to the right L5 foramen, which was also removed. A total gross resection was achieved ([Fig. 2]). The histopathological exam showed a nodular, partially capsulated, poorly cellular stromal neoplasm. It was composed of spindle cells and stellate cells with inconspicuous cytoplasm and oval hyperchromatic nuclei with low pleomorphism embedded in a rich myxoid matrix with sparse connective fibers, corresponding to an intramuscular myxoma ([Fig. 3]). Follow-up MRI after four months documented no evident residual or recurrent tumor ([Fig. 4]). The patient was asymptomatic and returned to her routine life.
Fig. 1 Lumbosacral spine: (A) T2-weighted MRI coronal view with hyperintense multilobulated paraspinal tumor. (B) sagittal view shows hypointense tumor on T1-weighted MRI. (C) axial and (D) sagittal CT scans demonstrate a low-density mass, with remodeling of adjacent bony structures.
Fig. 2 (A) Incision line. (B) paravertebral musculature containing an evident tumor mass. (C) Lumbosacral tumor in its entirety. (D) Removal of the tumor that extended into the vertebral foramen. (E) Tumor bed. (F) Tumor fragments.
Fig. 3 (A) Nodular, poorly cellular stromal neoplasm (HE, 20x); (B) cells embedded in a rich myxoid matrix with sparse connective fibers (HE, 100x); (C) and (D) spindle cells and stellate cells in a rich myxoid matrix (HE, 600x).
Fig. 4 Lumbar postoperative spine MRI: (A) axial, (B) coronal and (C) sagittal reconstructions show total removal of the tumor.
Discussion
In 1863, Virchow introduced the term Myxoma to describe a tumor that histologically resembles the umbilical cord.[1]
[2]
[4] Only in 1948 histological criteria were established for its diagnosis, by Stout in 1948, who stated that myxoma is a true mesenchymal neoplasm composed of undifferentiated star cells in a myxoid stroma with delicate reticulin fibers.[1] In 1965, Erzinger and Weiss classified IM as a distinct subtype.[1] IM usually arises as a single lesion, although they can be seen as multiple lesions associated with fibrous bone dysplasia, Mazabraud syndrome, or as part of McCune-Albright syndrome (characterized by polyostotic fibrous dysplasia, café-aú-lait spots, and endocrine hyperfunction).[1] Although presumptive diagnosis can be yielded from clinical and imaging findings, the definitive diagnosis requires anatomopathological evaluation.[5]
Paraspinal IM presents as a solitary painless mass in the dorsal region. Current imaging techniques for IM workup include ultrasound (USG), computed tomography (CT), and magnetic resonance (MR). On USG, IM appears as a hypoechoic lesion with a well-defined margin. Anechoic cystic foci may be present.[6] Intramuscular myxomas tend to show similar imaging patterns in both CT and MR which include the intramuscular localization, edges of the tumor with similar aspect to the bone marrow, and high water content. Thus, it is hypodense in CT, whereas, in MRI, it presents as a lesion hypointense in T1 and hyperintense in T2.[7] Additionally, it may appear as a well-defined ovoid (65%), lobulated (30%), or spherical lesion (5%), with fluid-like signal intensity and a peritumoral fat rim on T1-weighted MR images, and present with an increased signal in the adjacent muscle on T2-weighted or fluid-sensitive MR sequences.[7] The latter two features have not been previously emphasized and are the most reliable radiologic features for differentiating intramuscular myxoma from other myxoid soft-tissue lesions.[7]
Differential diagnoses include more aggressive neoplasms such as angiomyxoma, myxoid neurofibroma, low-grade fibromyxoid sarcoma, myxoid liposarcoma (ML), cellular myxoma, juxta-articular myxoma, and nodular fasciitis.[2] IM is of particular interest to radiologists because it may have imaging features similar to other myxoid lesions, especially the ML, which makes their imaging differentiation often challenging.[7] For example, in cases with a predominantly myxoid morphology (cystic appearance) and intramuscular location, ML may strikingly resemble an IM in the image.[7] These similarities extend to the gross and histological appearances as well, and differentiating between the two may also be difficult.[7] The correct diagnosis is of utmost importance as IM has a benign clinical course, with no tendency to recur or metastasize, whereas other neoplasms may require adjuvant treatment and carry a worse prognosis.[7]
[8]
[9] At last, neurogenic tumors should be considered, as these are intermuscular, which may be confounded for an intramuscular lesion. Nonetheless, they often show an entering and exiting nerve on imaging, and with the “target sign” on T2-weighted MR imaging.[10]
The treatment of choice for IM is surgical excision. Throughout the literature, there were no reports of their metastatic spread or malignant transformation, although local recurrence/progression is possible when the surgical procedure consists of enucleation or incomplete resection.[1]
[4] Therefore, wide excision with clear margins is recommended.[3]
[10]
Conclusion
In conclusion, IM of the lumbosacral paraspinal muscle is a rare entity and, up to this date, no cases have been reported on the Brazilian population. It must be part of the differential diagnosis of paraspinal tumors. The precise diagnosis may be challenging due to radiological/histological similarity to other entities, especially soft tissue sarcoma, but it is of utmost importance to define management.
