Imaging Features of Primary and Secondary Adult

RhabdomyosarcomaSaboo SS, Krajewski KM, Zukotynski

K, Howard S, Jagannathan JP, Hornick JL et al.

JOURNAL READING

• Objective. RM are rare & aggressive soft tissue sarcomas in adults. The purpose of this article is to describe the imaging features of primary & secondary adult RM utilizing MRI, CT,& F-FDG PET/CT

• Conclusion. MRI is the imaging tech of choice for the evaluation of primary RM. CT & F-FDG PET/CT play major roles in the evaluation of metastatic disease.

Introduction

• RM is a malignant neoplasm of striated muscle or its precursor mesenchymal cells that occurs rarely in adults (3%) but most common in children (>50%) with 72-81% <10yr.

Pathology, Clinical Features, and Prognosis

• RM : embryonal, alveolar, and pleomorphic types.

• Embryonal (49%), alveolar (30%) --> Predominantly seen in childhood.

• Clinical sympt : depending on the location of the primary tumor & the presence of metastasis.

• RM : head, neck, trunk, and extremities including sites lacking normal striated muscle.

• Most common site in adult : extremities (26% of cases), and the head and neck parameningeal region--is the most common in children (25% of cases).

• From 2002&2003 : 29-52% for head & neck, 22-27% for extremities, 12-20% for genitourinary region, 9% for body wall, and 2-13% for abdomen.

• Pleomorphyc subtype : adult >45yr, and the alveolar subtype : 10-25yr

• Microscopically

1. Embryonal RM consists of : Sheets of rounded to short spindle cells, often with loose myxoid foci, containing variable number of eosinophilic rhabdomyoblasts.

2. Alveolar RM : undifferentiated uniform round cells in an alveolar pattern or in diffuse sheets with occasional characteristic multinucleated ("wreath like") giant cells.

• Pleomorphic RM : sheets and fasicles of highly pleomorphic cells with brightly eosinophilic cytoplasm.

• Sclerosing RM : dense hyaline matrix-containing lobules and infiltrating cords of small round malignant cells but without calsification.

• Prognostic factors include the site, size, patient age, tumor resectability, surgical margins, and presence of metastases.

• Adult RM--> higher mortality rates then those in children.

CT and MRI Features of Primary Adult RM

• MRI is the imaging modality of choice for the assessment of primary tumor site in most patient with RM.

• MRI & CT beneficial in evaluating tumors of head &neck : superior cortical bone evaluation (CT) and the better bone marrow assessment & soft-tissue (MRI).

• Contrast-enhanced CT : most commonly used modality for sarcoma staging (chest and abdomen), particularly to assess metastatic spread to lungs.

• MRI :best modality for evaluation tumors in the pelvis and extremities.

• IV gadolinium : based contrast agent routinely in MRI.

• Imaging appearance : large mass with intermediate to-low signal intensity compared with muscle on T1-weighted imaging, high signal intensity on T2WI, & heterogenous contrast enhancement.

• Imaging plays important role in the preoperative and postoperataive.

Embryonal RM (of Head and Neck)• CT seen as : homogenous masses with ill-

defined margins and minimal necrosis, causing destruction of adjacent bone.

• Display : moderate enhancement on contrast-enhanced T1-weighted imaging and heterogenously hyperintense signal on T2WI and STIR sequences.

Alveolar and Pleomorphic subtype

• Seen as : large partly necrotic tumors, often with a lobulated margin and lymphovascular invasion.

• Display: moderately hyperintense with heterogenous signal on both T2WI and STIR sequences and moderate to marked heterogenous enhancement on contrast-enhanced fat suppressed T1WI.

Pleomorphic subtype• Markedly : hyperintense on both T2WI and

STIR sequences. They are isointense to hyperintense to muscle on T1WI.

• On contrast enhanced CT : heterogenously isodense to hyperdense to muscle with areas of necrosis.

• On imaging : irregular arrangement of cells &necrosis.

Sclerosing subtype

• MRI : similar to pleomorphic subtype.

These masses can be predominantly isointense on T1WI and hyperintense on T2WI with heterogenous enhancement on contrast enhanced images, but can appear hyperintense on T1WI because of predominant hyaline collagenous stroma.

FDG PET/CT in Adult RM• Can improve patient treatment through

more accurate staging, can also help to detect widespread bone marrow disease, and helpful to guide biopsy to the most metabolically active site of disease.

• This includes greater accuracy in detecting lymph node disease and distant metastases.

Secondary Adult RM• Lymph node involvement : 33-45%

patients with adult RM as compared with 15-20% in pediatric RM (much higher incidence of alveolar subtype).

• Lung is the most common site of metastasis, followed by bone, bone marrow, and lymph nodes.

• Other : pancreas, liver, rarely breast, peritoneum and muscle.

Differential Diagnosis

• Other soft tissue sarcomas, lymphoma, and carsinoma must be considered.

• To confirm : histopatologic examination ad immunohistochemistry are necessary.

Treatment

• Local surgical resection, local radiation therapy, and systemic chemotherapy.

• Complete surgical resection : curative therapy.

• Adult RM : relatively less radiosensitive and chemosensitive than pediatric.

• Chemo regimen : vincristine, actinomycin-D, doxorubicin, cyclophopamide, ifosfamide, & etoposide in various combination and high dose in metastasis.

• Metastatic lymph node radiation is recommended for all patients with alveolar RM.

Conclusion

• RM is a rare highly aggressive soft tissue sarcoma with poor prognosis in adult.

• MRI : imaging modality of choice primary RM.

• CT & FDG PET/CT: helpful for evaluation of nodal and metastatic disease.

• Imaging features of a large heterogenous primary tumor, wide-spread lymphadenopathy, and pulmonary and osseus metastases, along with the combination of clinical findings, age, and site --> can help to narrow the DD, because imaging findings alone are nonspesific in the diagnosis of RM in the adult population.

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