Hamartoma overview

# Overview
A hamartoma (from Greek hamartion bodily defect) is a focal malformation that resembles a neoplasm in the tissue of its origin.  Hamartoma is a non-malignant tumor, and it grows at the same rate as the surrounding tissues. It is composed of an overgrowth of mature cells and tissues that normally occur in the affected area. They emerge in many different parts of the body and are most often asymptomatic and undetected unless seen on an image taken for another reason (incidentaloma). The most common hamartomas occur in the lungs. About 58% of all solitary lung nodules, and about 75% of all benign lung tumors, are hamartomas. Hamartomas mostly arise from connective tissue and are generally formed of cartilage, fat, and connective tissue cells, although they may include many other types of cells. Hamartomas must be differentiated from other diseases that cause abnormal tissue growth and calcification, such as calcified metastases and lipomas. Surgery is the mainstay of treatment for hamartomas.

# Historical Perspective
Hamartomas were first described by Eugen Albrecht, a German pathologist, in 1904.

# Classification
Hamartomas may be classified into different types based on their location, such as: lung (most common), heart, hypothalamus, kidneys, or spleen. Other classifications can consider lesion class, dividing hamartomas into 4 different categories, such as bone-forming, cartilage-forming, fiber-forming and benign nonmatrix-forming.

# Pathophysiology
Hamartomas arise from connective tissue and are generally formed of cartilage, fat, and connective tissue cells, although they may include many other types of cells. They can be located in lung (most common), heart, hypothalamus, kidneys, or spleen. The pathogenesis consists primarily of disorganized replication of normal tissue cells. There are many genetic syndromes that cause multiple hamartomas, such as Peutz-Jeghers syndrome, PTEN hamartoma tumor syndrome, and Cowdens syndrome. Genes involved in the pathogenesis of harmatomatous syndromes include: BMPR1A, SMAD4, PTEN, and STK11.

# Causes
The causes of hamartomas have not been identified.

# Epidemiology and Demographics
The incidence of pulmonary hamartoma is approximately 0.25% in general population. The incidence of other hamartomas remains unknown. Pulmonary hamartomas are estimated to be 8% of all lung neoplasms. Most lesions are diagnosed incidentally. Hamartomatous syndromes are usually first diagnosed among adolescents and adult patients. In general, most hamartomas affect males more commonly than females.

# Risk Factors
The most potent risk factors in the development of hamartomas are familial hamartomatous syndromes, such as: Cowdens syndrome, Peutz-Jeghers syndrome, juvenile polyposis syndrome, PTEN hamartoma tumor syndrome, hereditary mixed polyposis syndrome, tuberous sclerosis, and Bannayan-Riley-Ruvalcaba syndrome.

# Screening
Screening for sporadic hamartoma is not recommended. However, according to the American College of Gastroenterology (ACG), screening for multiple hamartomas by genetic evaluation is recommended among patients with hamartomatous polyposis syndromes, such as juvenile polyposis syndrome, Peutz-Jeghers syndrome, and Cowdens syndrome.

# Differentiating Hamartoma from other Diseases
Hamartomas must be differentiated from other diseases that cause abnormal tissue growth and calcifications, such as calcified metastases, and lipomas.

# Natural History, Complications and Prognosis
If left untreated, hamartomas normally grow slowly and may progress to develop a considerable size, however pulmonary hamartomas have low or no malignant potential. Nevertheless, it is essential to rule out the presence of cancer. Common complications of hamartomas will depend on the location and size. Prognosis is generally regraded as excellent.

# Diagnosis

## Staging
There is no established system for the staging of hamartomas.

## History and Symptoms
Hamartomas are usually asymptomatic. However, in some cases such as, hypothalamic hamartomas and pulmonary hamartomas, symptoms may be more noticeable. In hypothalamic hamartomas, gelastic seizures, visual problems, early onset of puberty, and behavioral problems are the most reported. On the other hand, symptoms of pulmonary hamartoma may result as a respiratory obstruction and include chronic cough, hemoptysis, or fever.  It is important to obtain the history about familial inheritance, as it provides insight into the associated conditions.

## Physical Examination
Patients with hamartoma usually have a normal appearance. Physical examination shows no remarkable findings.

## Laboratory Tests
There are no diagnostic laboratory findings associated with hamartoma. However, in some cases complete blood count, serum electrolytes, urea, and alkaline phosphatase levels may be indicated if the tumor becomes symptomatic.

## Chest X-Ray
On chest radiography, lung hamartomas are characterized by showing a sharply demarcated pulmonary nodule and popcorn calcifications (feature of chondroid calcification in hamartomas).

## CT
CT scan is the imaging modality of choice for the diagnosis of pulmonary hamartoma. On CT scan, hamartoma is characterized by focal collections of fat, a lesion with a smooth edge, and collections of fat alternating with foci of calcification.

## MRI
MRI is the modality of choice for assessment of hypothalamic, spleen, kidney, and other abdominal hamartomas. On MRI, hamartoma is characterized by a heterogeneous signal in T1 and high signal due to fat and cartilaginous components in T2.

## Ultrasound
On ultrasound, splenic hamartomas are hyperechoic solid masses, with or without cystic changes, and are hypervascular in Doppler ultrasound.

## Other Diagnostic Studies
Bronchoscopy may be useful to obtain biopsy and evaluate symptomatic bronchial hamartomas.

# Treatment

## Medical Therapy
There is no medical therapy for hamartomas; the mainstay of therapy is surgical treatment.

## Surgery
Surgery is the mainstay therapy for hamartomas.

## Primary Prevention
There is no established method for prevention of hamartomas.

## Secondary Prevention
Secondary prevention strategy for multiple hamartoma syndromes includes periodical imaging surveillance with CT scan.