Orbital haemangiopericytoma is a rare soft-tissue neoplasm. This tumour originates from pericytes found around capillaries. Pericyte is a spindle shaped cell with a moderate amount of cytoplasm and an indistinct border. Routine histopathologic differentiation of pericyte from fibroblast, histiocyte and endothelial cell is difficult. Cellular differentiation may be best achieved by electron microscopy and immune-histochemistry.The function of pericytes is uncertain but is believed to provide mechanical support to the capillaries. Pericytes morphologically resemble smooth muscle. Besides the muscle cone of the eye, this tumour may also affect optic nerve meninges and lacrimal sac. This rare tumour is commonly encountered in lower extremities and retro-peritoneum.
Median age of occurrence is fourth decade, but haemangiopericytoma has been noted from 20 months to 87 years of age. The occurrence of tumour in orbit is more common in males.
Orbital haemangiopericytoma has similar signs and symptoms, and imaging study findings as orbital cavernous haemangioma. The tumour generally present with proptosis, diminution of vision, diplopia, and swelling. However, haemangiopericytoma may be more aggressive, extend throughout in orbit, and may even invade the cranial cavity. About one-third of Orbital haemangiopericytoma have histopathologic criteria compatible with malignancy. Distant metastasis of the tumour is uncommon.
References
http://eyewiki.aao.org/Hemangiopericytoma
http://www.scielo.br/pdf/rbcp/v27n3/en_29.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3862697/
Symptoms may include
Frequent intracranial extension and involvement of nasal sinuses may produce additional symptoms.
There is controversy about the existence of haemangiopericytoma. Its derivation from pericytes is questioned and cases have been reclassified as solitary fibrous tumours, based on histopathologic and immune-histochemical findings. Traditionally, it has been categorised as vascular tumour.
Orbital haemangiopericytoma is believed to originate from extra-vascular pericytes, morphologically resembling smooth muscles around capillaries or from primitive mesenchymal cells. The function of pericyte is uncertain, but is believed to provide mechanical support to the capillaries, and may be having contractile function.
Orbital haemangiopericytoma occurs mainly in adults and has similar symptoms, signs, and imaging studies as cavernous haemangioma. Haemangiopericytoma may be more aggressive with time, extend throughout the orbit, and even invade the cranial cavity.
The main clinical features are proptosis and mass effect due to swelling, predominantly in the superior part of orbit, usually not associated with pain, features of infiltration, or entrapment. Patients usually have symptoms for less than one year on presentation, but there may be variation from one month to twenty six years.
Investigations:
Histopathology:
Tumour shows uniformly cellular pattern with a sinusoidal vascular component often forming branching (stag horn) channels. Reticulin forms a dense mesh around individual cells. Pericytes show staining for vimentin (protein seen in mesenchymally derived cells) only.
In addition, haemangiopericytoma show myxoid, cellular and cystic component. Giant cells may be seen as well as areas of haemorrhage, necrosis and hyalinisation.
Three patterns have been described:
Histopathologically, haemangiopericytoma is divided into three types:
Benign tumour shows minimal atypical cells with few mitotic figures. Intermediate and malignant tumour shows increasing mitosis, pleomorphism, necrosis, haemorrhage, compression of vascular spaces, and infiltrative margins. These tumours also show higher rate of metastasis as compared to benign one. However, distant metastasis is uncommon.
Differential diagnosis:
Optic nerve meningioma and dural sarcoid also needs to be differentiated, in cases where haemangiopericytoma arises from dural sheath.
Management of the tumours is mainly surgical.
Surgical therapy
Local recurrence may occur with incomplete or piecemeal excision. Recurrence is higher in malignant and borderline types. Even histologically diagnosed tumours may also recur or show distant metastasis. Since local recurrence and metastatic disease is a significant risk in these tumours, long term follow up (at least ten years) is necessary to ensure complete cure.
Orbital recurrence may require wider orbital exenteration, irradiation, or chemotherapy.
Radiotherapy
Radiotherapy is not much of benefit and it may precipitate sarcomatous changes as well.
Prognosis
Since even more histologically benign lesions may result in clinically invasive disease or malignant transformation, the aggressiveness of a particular lesion is difficult to predict. Therefore, this tumour warrants aggressive surgery and often adjuvant therapy.
