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Neuroradiology Case of the Week

Case 312

Adam J. Weller, MSIV

Clinical Presentation: Patient is a 4-year-old male with nasal congestion and loss of vision in the right eye.

Imaging Findings: A large, heterogeneous enhancing mass is seen centered over the right masticator space. It extends posteriorly into the basisphenoid and right petrous temporal bone, laterally to the body of the right mandible, anteriorly into the right maxillary sinus and right nasal cavity, and medially across midline and into the left cavernous sinus and sella. The mass is also seen invading the right orbit via the superior orbital fissure. Inferiorly, the mass extends to the palate. The mass is heterogeneously hyper-intense on T2 weighted images and shows low signal on T1 weighted images. MRA showed narrowing of the cavernous segment of the right internal carotid artery; however, the vessel remains patent. These findings are suggestive of a lesion with malignant etiology. Follow up CT of the chest and neck showed no evidence for metastatic disease

Diagnosis: Rhabdomyosarcoma

Discussion: Rhabdomyosarcoma is a malignant tumor that is thought to be caused by primitive mesenchyme that has not lost its capacity to form striated muscle. Most commonly, it is a tumor of the head and neck (30-40%), but can also be found in other locations such as the extremities (18%), the genitourinary tract (18%), the trunk (11%), and the retroperitoneum (6%). It is also known to metastasize to the lung, bone marrow, lymph nodes, breast, and brain.
      Rhabdomyosarcoma is primarily a tumor in children. 90% occur in patients under the age of 25, 60-70% of which are actually under the age of 10. In fact, it is the most common soft tissue sarcoma in children. The clinical presentation is typically related to the mass effect of the tumor, such as in this case where the tumor had invaded into the right orbital space from the nasal cavities and therefore presented as decreased vision in the right eye and nasal congestion. When symptoms are suspicious for rhabdomyosarcoma, the work-up includes imaging, to confirm a mass and determine extent. If a mass is confirmed, a biopsy is required to determine the nature of the tumor, and a survey for metastasis should be undertaken.
      There are five major histological groupings of rhabdomyosarcoma. Embryonal is the most common type found in children and rarely originates in a striated muscle bed. The Alveolar subtype is the next most common and is seen more frequently in adolescents and typically arises from a striated muscle beds in the extremities. Alveolar rhabdomyosarcoma is associated with the worst prognosis by type. The last three subtypes only make up about 10% of cases and include from most to least common: boytroid, spindle cell, and anaplastic rhabdomyosarcoma.
     The treatment of rhabdomyosarcoma is a combination of surgery, chemotherapy, and radiation. Early diagnosis and treatment greatly improves the prognosis as the extent of the lesion is the determining factor. If there is only localized disease then the 5-year survival is greater than 80%; however, if there is evidence of metastasis then the 5-year survival is reported to drop to less than 30%. Other factors influencing prognosis are age of onset and tumor load at diagnosis.

References:

1. Ferguson MO, Lee SC. Pathology: rhabdomyosarcoma. Emedicine, June 20, 2005. http://www.emedicine.com/ent/topic641.htm
2. Cripe TP. Rhabdomyosarcoma. Emedicine, October 4, 2006 http://www.emedicine.com/ped/topic2005.htm
3. Yousem DM, Lexa FJ, Bilaniuk LT, Zimmerman RI. Rhabdomyosarcomas in the head and neck: MR imaging evaluation. Radiology. 1990 Dec;177(3):683-6. [Medline]
4. Lee JH, Lee MS, Lee BH, Choe DH, Do YS, Kim KH, Chin SY, Shim YS, Cho KJ Rhabdomyosarcoma of the head and neck in adults: MR and CT findings. AJNR Am J Neuroradiol. 1996 Nov-Dec;17(10):1923-8. [Medline]