Pancreatic hamartoma is a nonneoplastic, mass-forming lesion of the pancreas and is extremely rare. Most cases reported in the literature as hamartoma appear to be examples of chronic pancreatitis in which pancreatic elements are haphazardly distributed in a hamartomatous fashion. Recently, true hamartomas of this organ have been characterized. Pancreatic hamartoma is divided into two subgroups: solid and cystic, and solid pancreatic hamartoma [2
summarizes the clinicopathological features of pancreatic hamartoma that have been reported in the literature. Pancreatic hamartoma can occur at any age (34 weeks to 62 years), but the average age of occurrence was 40 to 50 years (median, 46 years). The reported male-to-female ratio was 1:0.7. Eleven hamartomas were located in the head of the pancreas, four in the body or tail, one in the neck, and another occupied the entire pancreas. The average size of the mass was 4.32 cm (range, 0.9 to 11.5 cm) [1
Clinicopathological features of pancreatic hamartoma reported in the literature
Pancreatic hamartoma is composed of three disarranged cellular components in varying proportions: acinar, islet, and ductal cells. But the pathogenesis of pancreatic hamartoma is still controversial. Although this tumor has been previously investigated by immunohistochemical, ultrastructural, and molecular biological studies, the precise mechanisms of its pathophysiology remain unknown.
The signs and symptoms are nonspecific. Most patients are asymptomatic or have vague symptoms (). Abdominal ultrasonography (US), CT, and MRI can be employed for preoperative diagnosis of hamartoma. US shows hyperechoic solid masses with or without a cystic change [6
]. On CT, the tumor is a well-circumscribed, iso- or hypoattenuated, solid and/or cystic mass, with heterogeneous contrast enhancement [2
]. MRI demonstrates a relatively well-defined mass. Although various imaging features can help, the diagnosis is often not direct. Pancreatic hamartoma can be difficult to diagnose preoperatively, and is usually diagnosed after pancreatectomy. In our case, the initial diagnosis was a solid pseudopapillary tumor or serous cystic neoplasm. However, the final diagnosis after surgical resection was pancreatic hamartoma. Thus, definitive diagnosis requires pathological examination of the excised lesion.
In pancreatic hamartoma, microscopic salient findings are a circumscribed lesion that is composed of a disorderly arrangement of well-differentiated endocrine and exocrine pancreatic tissue, and some cystically dilated ducts [2
]. Immunohistochemically, the diagnosis of pancreatic hamartoma is supported by stromal cells that are positive for CD34 and/or CD117 (c-kit) [1
]. CD34 is a myeloid stem-cell marker and is thought to play an important role in maintaining stromal integrity and inhibition of tumor cell migration. The fibroblasts in neoplastic and inflammatory pancreatic lesions have been described to express CD34 [10
]. CD117 is a transmembrane tyrosine kinase receptor for stem cell factor and is encoded by the proto-oncogene c-kit [2
]. c-kit mutations have been found in mast-cell tumors and gastrointestinal stromal tumor (GIST). In our case, the tumor was positive immunohistochemically for CD34, and positive/negative for c-kit. Thus, a diagnosis of GIST was excluded. The treatment of pancreatic hamartoma is surgical resection if possible.
In conclusion, diagnosis of pancreatic hamartoma is difficult preoperatively and is usually confirmed pathologically after surgery. Therefore, although extremely rare, pancreatic hamartoma should be taken into consideration as a differential diagnosis of a pancreatic tumor.