Thymolipomas are rare benign slow-growing tumors, which present equally in males and females. They are diagnosed mostly in young adults with a mean age of 27 years. Approximately half of the patients are asymptomatic. There are less than 140 reported cases. It accounts for 2 - 9 % of thymic neoplasms. About 15% of the patients will present within first decade of life and 80% will present in the first four decades. Lange 1916 published the first lipoma of the thymus case 9, 10. And it wasnÕt until 1948 when the term Thymolipoma was introduced into literature by Hall.
There are several theories to explain the development of thymolipoma. The first one is simple thymic and fatty hyperplasia, or the second one a true mixed endocrine and mesodermal neoplasm. The third theory is a fatty neoplasm. Rosado-de- Christianson et al in Radiology 1994 reported 27 cases series of thymolipoma, 56% presented with upper respiratory tract infection, chest pain, dyspnea and chronic non-specific chest heaviness. Histopathology study of this tumor reveal a large, soft, encapsulated mass composed of mature adipose cells and thymic tissue. Twenty-five percent of thymolipoma tumors weigh more than 2 kg.
Thymomas are the most common primary tumor of the anterior mediastinum in adults. They are rare in children and adolescents. One third of those patients will experience chest pain, cough, dyspnea, and/or other compressive symptoms. Half of the patients suffer from one or more parathymic syndromes, most commonly myasthenia gravis, hypogammaglobulinemia, and pure red cell aplasia. Myasthenia gravis occurs in 30 to 50% of patients.
Thymomas are mostly solid, one third has necrosis, hemorrhage, and cystic areas. Chest X-ray usually shows well-defined, rounded, or lobulated anterior-superior mediastinal mass.
Thymic Carcinoma occurs in middle-aged men with mean age of 46 years. They are squamous cell carcinomas and lymphoepithelioma-like carcinomas. Metastasis to regional lymph nodes and distal sites are common and treatment is combined chemotherapy and radiotherapy. Thymic Carcinoid is a rare malignancy, affects men in the fourth to fifth decades of life. It is identical to carcinoid tumor at other site. Regional lymph node and distal metastasis especially bone metastasis is very common in 73% of the cases. Treatment is by complete surgical excision followed by radiotherapy and chemotherapy.
Nonneoplastic Thymic Cysts compromise 3% of the anterior mediastinal masses; they are either congenital or acquired (inflammation or neoplasm, such as lymphoma). Treatment is by surgical excision. Mediastinal Germ Cell Tumor composed of Teratomas, seminomas and nonseminomatous malignant germ cell tumor, which account for 10 to 15% of adult anterior mediastinal tumors. The most common extragonadal primary site is the anterosuperior mediastinal portion. The mean age at presentation is 27 years old. There is elevated a-fetoprotein (AFP) and b- HCG markers. On radiologic studies up to 26% exhibit calcification in the tumor. In the other hand Mediastinal Lymphangioma are benign proliferations of lymphatic vessels, which present in very young children. 50% will present at birth and 90% by 2 years of age. Lymphangioma mainly are located in the neck or axilla (95%) and 10% will extend into the anterior mediastinum. They require surgical resection.
FINAL THOUGHTSThis was a very large Thymolipoma that most likely was growing with the child for long time because of the deformity in the shape of her chest and the symptomatology from infancy.
A lesson from the case is to consider a more extensive different diagnosis when the patient is clearly not responding to maximum inhaled anti asthma therapy in a short time period.