What is a hamartoma?
A hamartoma is a benign (non-cancerous) overgrowth of a mature cell type normal to the site, tissue, or organ. The word is from the Greek hamartia (‘fault’ or ‘defect’) and -oma (‘tumour’ or ‘neoplasm’).
In the skin, a hamartoma often presents as a birthmark (congenital naevus), but may develop in adulthood (acquired).
Who gets hamartomas?
In general, hamartomas affect those aged 40–70, and males more than females. The incidence of many hamartomas is unknown and varies depending on type. The reported incidence rate of pulmonary hamartoma is 0.25%, while that of breast hamartoma is 0.1–0.7%.
Hamartomas are more common in conditions such as tuberous sclerosis complex and Cowden syndrome. Other risk factors include age, hormonal factors, obesity, family history, and genetic predisposition.
Some hamartomas are more commonly encountered in children. These include cardiac hamartomas, lipofibromatous hamartoma of the nerve, hypothalamic hamartoma, and Peutz-Jeghers syndrome.
What causes hamartomas?
Unlike a malignant tumour, hamartomas usually originate from the overgrowth of multiple aberrant cells rather than a singular mutated cell. Hamartomas cause a structurally disorganised malformation local to the original tissue but are non-neoplastic and rarely invade or significantly compress surrounding structures. It is possible to have neoplastic evolution within some hamartomas.
The underlying mechanisms of hamartomas are not fully understood. They are present in a broad spectrum of disorders and syndromes. Certain gene mutations have been associated with their development, including PTEN, SMAD4, STK1, BMPR1A, TSC-1, and TSC-2.
What are the clinical features of a hamartoma?
Hamartomas are distinctly demarcated masses that contain a variety of cell types depending upon their origin. Size is variable, mostly ranging between 1–4 cm, while some pulmonary hamartomas can be as large as 10 cm.
Cutaneous hamartomas may be verrucous, sebaceous, fibrous, achromatic, pilar, or other.
Clinical features vary depending on the location of the hamartoma and, consequently, the mass effect or localised pathology that may arise.
- Hamartomas in the brain may cause seizures, abnormal mental states, visual or sensory changes, behavioural changes, and endocrine abnormalities.
- Hamartomas in the heart can cause cardiac symptoms including chest pain, palpitations, shortness of breath, and heart murmurs or arrhythmias.
- Hamartomas in the lung can cause cough and haemoptysis.
Other potential symptoms include abdominal or flank pain, fevers, night sweats, and breast or testicular enlargement.
What are the different types of hamartomas?
Below are examples of different types of hamartomas.
Skin hamartomas
- Congenital melanocytic naevi (CMN) — composed mostly of melanocytes
- Sebaceous naevus
- Basaloid follicular hamartoma — found in Gorlin syndrome
- Chondroid syringoma (apocrine mixed tumour)
Other hamartomas
- Cardiac rhabdomyoma – hamartoma of altered cardiac myocytes
- Median nerve hamartoma
- Hypothalamic hamartoma – in Pallister-Hall syndrome
- Myoepithelial hamartoma – in the pancreas
- Lisch nodules – pigmented hamartomas in the iris, found in neurofibromatosis type 1
- PTEN hamartoma tumour syndromes (PHTS)
- Cowden syndrome (multiple hamartoma syndrome) — a genetic disorder characterised by multiple hamartomas in the skin
- Adult Lhermitte-Duclos disease — hamartomatous outgrowths of the cerebellum
- Bannayan-Riley-Ruvalcaba syndrome (see: Skin signs of gastrointestinal disease)
- Proteus syndrome
- Proteus-like syndrome
- Peutz-Jegher polyps of the bowel
- Neuroepithelial cells in tuberous sclerosis
- Sometimes considered benign neoplasms:
- Liver adenoma
- Kidney cyst.
How is a hamartoma diagnosed?
Diagnosis of a hamartoma varies depending on the type. In general, they are often diagnosed with a combination of laboratory testing, imaging (eg, x-ray, ultrasound, CT scan, or MRI), and biopsy for tissue diagnosis.
What are the histopathological features of a hamartoma?
On histopathological examination, hamartomas resemble benign tumours, and may include disorganised overgrowth of normal tissue. The cells cytologically resemble local tissues, and may be well-circumscribed.
There are not usually any signs of invasion into surrounding tissue or metastasis.
Specific histopathological characteristics depend on the type of hamartoma, for example:
- Neurocristic hamartoma pathology
- Folliculosebaceous cystic hamartoma pathology
- Neurofollicular hamartoma pathology
- Fibrous hamartoma of infancy pathology.
What is the differential diagnosis for hamartoma?
Differential diagnoses of a hamartoma include different types of benign or malignant tumours. The types of growths or neoplasia considered may be specific to the site involved.
What are the complications of a hamartoma?
Hamartomas are usually asymptomatic. However, some can grow very large leading to disfigurement and pressure on surrounding structures. Depending on location, this can lead to complications such as seizures, airway obstruction, abdominal obstruction, heart failure, or breast deformity. Some hamartomas can also lead to infection, infarction, fracture, haemorrhage, or (rarely) neoplastic transformation.
How do you prevent hamartomas?
It is not known how hamartomas can be prevented.
What is the outlook for hamartomas?
Hamartomas are almost always benign and many are asymptomatic, although rarely malignant transformation may occur. Prognosis varies depending on the size and location of the hamartoma, as well as the health status and comorbidities of the patient.