Acute respiratory distress caused by massive thymolipoma.

Abstract: The authors present the case of a 40-year-old female with a massive anterior mediastinal tumor who presented with acute respiratory distress. She required emergent intubation and ventilatory support for respiratory compromise caused by lung compression. Preoperative computed tomographic scan results suggested a mediastinal lipomatous mass. Resection of the tumor resulted in immediate improvement in her pulmonary status. Because thymolipomas can attain enormous dimensions and compress adjacent structures, they should be resected at the time of diagnosis.

Key Words: anterior mediastinal mass, thymic neoplasms, thymolipoma

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Thymolipoma is a rare benign tumor of thymic origin that can achieve massive proportions before symptoms occur. These tumors account for 2 to 9% of thymic neoplasms, (1) with the majority being reported in children and young adults. (2) In young children, upper respiratory symptoms may develop because of their more compliant upper airways. (3, 4) However, most of the adult patients have no symptoms referable to the tumor, and are diagnosed after routine radiographic imaging. (5) This case illustrates the slow but progressive enlargement of these tumors, and the need for timely resection once diagnosis is made.

Case Report

A 40-year-old, morbidly obese female presented with severe dyspnea that had progressed over a period of 3 days. She also complained of productive cough, but had no fever or chest pain. Her medical history included bronchial asthma, obstructive sleep apnea, and tobacco abuse. In addition, 5 years before this admission, a computed tomographic (CT) scan performed after an abnormal chest radiograph revealed anterior mediastinal lipomatosis. Because she was asymptomatic at that time, the caring physician elected not to pursue further treatment. Physical examination revealed morbid obesity, facial hirsutism, diffuse expiratory wheezing, altered mental status, and pitting lower extremity edema. Initial vital signs included a blood pressure of 131/77, heart rate of 102, and temperature of 36.2[degrees]C. Her baseline oxygen saturation was 91%, but this quickly deteriorated to 61% upon admission. Abnormal laboratory findings included arterial blood gas with pH of 7.28, pC[O.sub.2] of 124, and p[O.sub.2] of 69, along with leukocytosis of 11,300 mg/dL. Because of impending respiratory collapse, she was emergently intubated. Chest radiography revealed a widened mediastinal silhouette and extensive bilateral lower interstitial infiltrates (Fig. 1).

A CT scan revealed a huge mass that occupied the entire anterior mediastinum with posterior and caudal displacement of both lungs (Fig. 2). No invasion of great vessels or other structures was noted. The mass consisted of fatty tissue elements interspersed with soft tissue; no calcifications were observed.

Because of the respiratory compromise and the benign radiographic appearance of the tumor, a preoperative biopsy was not obtained. She was taken urgently to the operating room, and a median sternotomy was performed. A large lipomatous mass was found occupying the entire anterior mediastinum draped over the pericardium, extending to both pleural spaces. There was no invasion of contiguous structures by the tumor, and it was easily dissected off of the surrounding organs. His tologic examination of the resected specimen revealed-thymolipoma without evidence of malignant degeneration (Fig. 3). Her postoperative course was complicated with pneumonia, which resolved with antibiotic treatment. At the time of discharge, she was breathing easily with stable room air oxygen saturations. However, she continues to have problems with asthma and obstructive sleep apnea.

Discussion

The diagnosis of an anterior mediastinal mass requires thorough clinical investigation complemented by sensitive radiographic imaging. The differential diagnosis includes thymoma, massive thymic hyperplasia, teratoma, thyroid goiter, and lymphoma. Patients with thymolipomas are usually asymptomatic. However, as these tumors enlarge, they can extend into both hemithoraces and compress the lungs and adjacent mediastinal structures. Symptoms may then present in the form of dyspnea, chest pain, obstructive pneumonia, cough, reactive airway disease, or respiratory compromise secondary to airway and parenchymal compression. (2,3)

CT or magnetic resonance imaging confirms the diagnosis of an anterior mediastinal mass, and may accurately identify these lesions, based on radiographic characteristics. In this case, the admission chest radiograph was nondiagnostic, probably because of poor imaging associated with the patient's large body habitus. CT scan, however, revealed extensive mediastinal lipomatosis, with compression but no invasion of adjacent structures.

The pathogenesis of thymolipoma remains controversial. (6) Although it originates within the thymus, the thymic tissue appears normal, without any morphologic features of a thymoma. One theory suggests that thymolipoma originates as a thymoma, with subsequent involution and replacement with adipose tissue. (7) Accordingly, the association of thymolipoma with myasthenia gravis and other autoimmune disorders suggests that these tumors are at least related. (8) On the other hand, Kitano et al (4) suggest that thymolipoma may be closely related to massive thymic hyperplasia, in which the thymic tissue is gradually replaced by adipose tissue over time. The normalization of lymphocytosis that occurs with resection of both massive thymic hyperplasia and thymolipoma lends some credibility to this theory. Regardless of origin, these tumors have entirely benign pathology.

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Tissue diagnosis of anterior mediastinal masses is preferred or required before resection. However, the radiologic manifestations of the tumor and the respiratory distress in this case obviated that need. Asymptomatic thymolipomas and even those found on incidental radiographs should be treated with complete resection because of the gradual enlargement with eventual compression of mediastinal structures. Because of the benign nature of these lesions, surgical resection is curative and provides immediate relief of symptoms.

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Conclusion

Patients with thymolipoma usually remain asymptomatic until the tumor achieves enormous proportions, causing airway and parenchymal compression. Because these tumors show progressive, gradual enlargement, surgical intervention is indicated. Resection is curative and results in immediate improvement of pulmonary status.

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Accepted April 7, 2004.

References

1. Shirkhoda A, Chasen MH, Eftekhari F, et al. MR imaging of mediastinal thymolipoma. J Comput Assist Tomogr 1987;11:361-365.

2. Rosado-de-Christenson ML, Pugatch RD, Moran CA, et al. Thymolipoma: analysis of 27 cases. Radiology 1994;193:121-126.

3. Gregory AK, Connery CP, Resta-Flarer F, et al. A case of massive thymolipoma. J Pediatr Surg 1997;32:1780-1782.

4. Kitano Y, Yokomori K, Ohkura M, et al. Giant thymolipoma in a child. J Pediatr Surg 1993;28:1622-1625.

5. Moran CA, Rosado-de-Christenson M, Suster S. Thymolipoma: clinicopathologic review of 33 cases. Mod Pathol 1995;8:741-744.

6. Rosai J, Kevin GD. Atlas of tumor pathology: tumor of the thymus. Armed Forces Inst Pathol Vol 1 1976:162-166.

7. Bieglow NH, Ehler AA. Lipothymoma: an unusual benign tumor of the thymus gland. J Thorac Surg 1952;23:528-538.

8. Zambudio AR, Lanzas JT, Calvo MJR, et al. Thymolipomas in association with myasthenia gravis. J Thorac Cardiovasc Surg 2001;122:825-826.

RELATED ARTICLE: Key Points

* Thymolipomas represent rare tumors of the mediastinum.

* Patients with thymolipoma are usually asymptomatic until the tumor attains huge dimensions.

* Timely resection remains the definitive treatment of choice.

Michael E. Halkos, MD, John D. Symbas, MD, and Panagiotis N. Symbas, MD

From the Division of Cardiothoracic Surgery, Joseph B. Whitehead Department of Surgery, Grady Memorial Hospital, Emory University School of Medicine, Atlanta, GA.

Reprint requests to Michael E. Halkos, MD, 438 Rock Springs Court, Atlanta, GA 30306. Email: [e-mail]