Case 37. (13 Jul 1998)
Diagnosis: Hamartoma
Chest radiograph shows a well-demarcated large mass
in the right suprahilar area. On pre-enhanced CT, a huge well-demarcated
heterogeneous density of mass composed of multiple popcorn-like and stippled
calcifications and low attenuated portion in the right upper lobe and tethered
to the right minor fissure. On post-enhanced CT, the large mass reveals
marginal well enhanced portion and mainly poorly enhanced portion including
typical calcifications. On microscopic findings, pulmonary parenchymal
hamartoma composed predominantly of irregular and broad cartilage masses.
The cartilage is surrounded by a rim of fat or fibromyxoid connective tissue.
The peripheries are lined by respiratory epithelium.
Hamartomas are the most common benign lung neoplasms
and pathologically composed of cartilage with clefts lined by bronchial
epithelium and fat, or cystic collections of fluid. Some authors prefer
the term ˇ°hamartochondromaˇ± or ˇ°chondromatous hamartomaˇ± to distinguish
these lesions from the much rarer vascular hamartomas that do not contain
cartilage.
Most tumors present as a solitary asymptomatic parenchymal
lung nodule that may gradually increase in size. Pulmonary hamartomas typically
are well-circumscribed solitary nodules, the majority smaller than 4 cm
in diameter, without lobar predilection. Approximately one-third have a
smooth outline, which may aid in differentiation from the almost invariably
lobulated pulmonary carcinoma. Over 90% are situated peripherally, with
8 % or less arising in central bronchi. The peripheral lesions are asymptomatic;
the endobronchial hamartomas may cause of bronchial obstruction and hemoptysis.
The average age at presentation of pulmonary hamartoma is 45 to 50 years.
They are rarely seen in children. The diagnostic radiograph finding of
popcorn pattern of calcification occurs in fewer than 30 percent of patients.
Percutaneous transthoracic needle biopsy yields diagnostic information
in as many as 85 percent of patients. The patient with peripheral hamartoma
may be safely observed, as malignant transformation is rare. The pulmonary
hamartoma can be specifically recognized when focal deposits of fat are
identified by a CT number in the -80 to -120 HU range. Hamartomas represent
a very small proportion of all pulmonary nodules, but because they are
frequently not recognized preoperatively, they account for 6-8% of all
resected pulmonary nodules. Cartilage is generally the dominant mesenchymal
component of the lesion, often leading to calcification. The larger the
lesion, the more likely that it will calcify. Definite calcification is
seen on plain film in up to 15%. Some researchers reported in 20 resected
solitary hamartomas of the lung. Analyzing the lesions histologically,
they found fatty tissue in 7 cases and chondroid tissue in 13 of 20. Some
reporters concluded that nodules measuring 2.5 cm of less with smooth edges
and demonstrating focal collections of fat (or fat alternating with areas
of calcification) warranted a firm diagnosis of hamartoma and should be
conservatively managed. Hamartomas can be multiple but rare.
References
1. Armstrong P. Neoplasms of the lung. In Armstrong P, Wilson
AG, Dee P, Hansell DM. Imaging of disease of the chest. St. Louis, Mosby.
1995: 272-368
2. Yamashita K, Matsunobe S, Tsuda T et al. Solitary pulmonary
nodule: preliminary evaluation with incremental dynamic study. Radiology.
1995;194:399-405
3. Naidich DP, Zerhouni EA, Siegelman SS. Computed tomography
and magnetic resonance of the thorax. New York. Raven Press. 1991 : 303-338
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