Positron Emission Tomography–Computed Tomography Figure 1: Axial Unenhanced Computed Tomography Image
Figure 2: Coronal Pre-/Post-contrast T1-weighted Magnetic Resonance Images
AB
The pre-contrast image (A) demonstrates a left maxillary sinus mass which is isointense to gray matter. The post-contrast (B) T1-weighted image demonstrates intense heterogeneous enhancement with non-enhancing cystic components as well as erosion of the cribriform plate. No definite invasion into the anterior cranial fossa is seen.
Figure 3: Low-power Micrograph of Solid-variant Alveolar Rhabdomyosarcoma with Cells
This image demonstrates a large mass of heterogeneous attenuation centered in the left maxillary sinus, with erosion of the maxillary sinus walls. Adjacent soft-tissue infiltration and left nasal cavity obstruction are also evident.
Oncologic staging using F18-FDG PET-CT revealed significant metabolic activity associated with the primary neoplasm in the maxillary sinus (see Figure 4). An enlarged ipsilateral level IIA lymph node in the neck with moderate metabolic activity (maximum standardized uptake value [SUV] 4.9) was demonstrated. Histopathologic study of this node revealed findings consistent with metastatic rhabdomyosarcoma. The PET-CT also demonstrated an osteolytic lesion in the ipsilateral left iliac bone with moderate hypermetabolism (maximum SUV 6.5) (see Figure 5); cytologic examination of this lesion also revealed malignant small round blue cells consistent with rhabdomyosarcoma. Cytologic examination of the cerebrospinal fluid was performed given the questionable intradural extent of the primary tumor, with no malignant cells identified. The patient was determined to have stage 4 disease and was enrolled in the Children’s Oncology Group ARST0431 trial, to include intensive multiagent chemotherapy with vincristine/doxorubicin/cyclophosphamide (VDC) and planned adjunctive regional external-beam radiation therapy at 20 weeks. Follow-up PET-CT four weeks after initiation of chemotherapy showed a favorable early metabolic response at the site of the primary lesion (see Figure 6) as well as within the nodal and osseous metastatic foci (see Figure 7). Repeat bone marrow cytology of the left iliac bone metastasis was repeated, with no malignant cells identified
Discussion
Although rhabdomyosarcoma is considered the most common pediatric solid tumor of the head and neck, it is a rare primary head/neck tumor in adult patients.1,2
Based on the modified World
Health Organization classification, two main morphologic subtypes are described: embryonal rhabdomyosarcoma (ERMS), which encompasses the botryoid subtype, and alveolar rhabdomyosarcoma (ARMS). The
US ONCOLOGY & HEMATOLOGY
This case also provides an example of the potential utility of PET-CT in following pathologically confirmed treatment response in the adult patient with ARMS. Here, the initial pre-treatment PET-CT
127
This image demonstrates positive immunoreactivity of the tumor to myo-D1, a nuclear regulatory protein in skeletal muscle differentiation. Note the underdevelopment of the alveolar pattern in this solid-variant specimen, which exhibits a paucity of intervening fibrous septae.
diagnostic distinction between ERMS and ARMS is important because the alveolar subtype portends a worse prognosis owing to more frequent metastatic dissemination, requiring a modified therapeutic regimen.2,3
The case described above is a rare case of primary ARMS in an adult patient with extensive local bony erosion and soft-tissue infiltration, ipsilateral nodal extension, and distant metastatic involvement. The tumor demonstrates a solid variant pattern of growth, as previously described by Tsokos and Triche.2,4
Positive staining for
desmin, a muscle-specific actin, and myo-D1, a myogenic nuclear regulatory protein,2,3
more common head/neck neoplasms such as squamous cell carcinoma, lymphoma, and melanoma.
provided precise diagnosis and eliminated other
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