Atypical Neurofibroma

Gregory S Hurlock, MD - Case Coordinator
Shital Rajni Shah, MD - Radiology Discussion
Jason H Smouse, MD - Pathology Discussion
Philip Costello, MD - Attending Radiologist
Pablo R Ros, MD, MPH - Attending Radiologist

July 28, 2003

Presentation

Imaging Findings

Posteroantior and lateral radiographs of the chest show a mass in the area of the left upper lobe. The trachea appears to be deviated slightly to the right. The lesion is likely within the superior, posterior mediastinum. This suggests paraganglioma, neuroblastoma, lymphoma, or aneurysm of the left subclavian artery (less likely).

Axial computed tomography images show the posterior mediastinal mass close to the trachea. The mass is well circumscribed and without calcifications. The contour is not particularly lobular. The subclavian artery is not visible on these slices. The mass appears to be homogeneous. Because the mass is isolated and not lobulated, lymphoma is less likely. It does not appear to be related to the vascular structures.

Diagnosis

Discussion

The gross specimen is a 9-cm, well-circumscribed but unencapsulated mass. The lesion has a fleshy, tan appearance with focal areas of hemorrhage. On cut section (not pictured), the appearance was homogeneous. Low-power microscopy shows a randomly arranged, vesicular growth pattern composed of spindle cells. The nuclei have a wavy pattern: a characteristically neural appearance. The cells are mixed with a fibromyxoid stroma. There is no increase in mitotic activity. Immunohistochemical staining (S100 and NFP) confirmed the diagnosis.

Radiology Discussion:

The differential diagnosis of a superior mediastinal mass is fairly long. Potentially involved structures include the thyroid, lymph nodes, trachea and esophagus, among others. Thyroid masses are typically indicated by a continuity of the lesion with the cervical thyroid gland. Thyroid goiter and carcinoma are the most common masses. Parathyroid masses should also be considered. Lymphoma and lymphangioma (a rare, benign tumor composed of dilated lymphatic channels and most often found in young children) must be included, as must nerve sheath tumors, such as schwannoma and neurofibroma. Squamous cell carcinoma, adenoid cystic carcinoma, and metastases may originate in the trachea, while leiomyoma, squamous cell carcinoma, and duplication cysts may arise in the esophagus.

Neurogenic tumors are divided into three categories, based on etiology. Tumors that arise in the peripheral nerves include schwannoma and neurofibroma. Ganglioneuroma, ganglioneuroblastoma, and neuroblastoma originate in the sympathetic chain. Pheochromocytoma and chemodectoma arise in the paraganglia.

Neurofibromas are composed of spindle cells that arise from the Schwann cells. The masses tend to be well encapsulated. Neurofibroma is a benign entity, although it may recur locally. There is no difference in incidence between genders; these tumors are typically found in younger patients (under 50 years). The diagnosis is associated with neurofibromatosis and the presence of multiple mediastinal masses. On CT, the characteristic appearance is that of a round, smooth paraspinal mass of homogeneously low density. The lesion may extend into the spinal canal via an enlarged intervertebral foramen creating a "dumbbell" appearance. On MRI, the lesion is slightly brighter than muscle on T1 and very bright on T2. It will enhance homogeneously with gadolinium contrast.

References

McCloud T. Thoracic Radiology: The Requisites. Mosby. St. Louis: MO, 1998, 431-463.

Klein J. Fundamentals of Diagnostic Radiology. Lippincott Williams & Wilkins. Philadelphia: PA, 1999, 319-343.

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