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What is Kasabach–Merritt syndrome and explain in detail?
Kasabach–Merritt syndrome, also known as hemangioma with thrombocytopenia, is a rare disease, usually of infants, in which a vascular tumor leads to decreased platelet counts and sometimes other bleeding problems, which can be life-threatening.  It is also known as hemangioma thrombocytopenia syndrome. It is named after Haig Haigouni Kasabach and Katharine Krom Merritt, the two pediatricians who first described the condition in 1940.

Signs and symptoms
Initially a vascular lesion is usually noted on the skin which can be firm and hard (indurated). Areas of tiny red dots (petechiae) can appear around the lesion or on other parts of the body. If the vascular lesion is internal, these petechiae and bruising can be seen on the skin. Bruising and spontaneous bleeding can also occur. The tumors are not hemangiomas. They usually present in young infants, less than three months of age, but have also been reported in the toddler age group. These tumors occur in the extremities, chest, neck, abdomen and pelvis. They infiltrate across tissue and can be aggravated by interventions, infection and trauma. When the tumors associated with KMP are internal such as in the chest or abdomen, they can cause significant illness and can be life-threatening due to bleeding. Internal lesions can take a longer time to diagnose.

Pathophysiology
Kasabach–Merritt syndrome is usually caused by a hemangioendothelioma or other vascular tumor, often present at birth. Although these tumors are relatively common, they only rarely cause Kasabach–Merritt syndrome.When these tumors are large or are growing rapidly, sometimes they can trap platelets, causing severe thrombocytopenia.  The combination of vascular tumor and consumptive thrombocytopenia defines Kasabach–Merritt syndrome.  Tumors can be found in the trunk, upper and lower extremities, retroperitoneum, and in the cervical and facial areas.This consumptive coagulopathy also uses up clotting factors, such as fibrinogen which may worsen bleeding.  The coagulopathy can progress to disseminated intravascular coagulation and even death. Hemolytic anemia secondary to microangiopathic destruction (physical damage) of the RBCs can be expressed as mild, moderate, or severe.

Diagnosis
The diagnostic workup is directed by the presenting signs and symptoms, and can involve:

blood counts, clotting studies, and other laboratory testing
imaging tests (ultrasound, CT scan, MRI, sometimes angiography, and rarely nuclear medicine scans)
Biopsy of the tumor is contraindicated due to risk of bleeding.Patients uniformly show severe thrombocytopenia, low fibrinogen levels, high fibrin degradation products (due to fibrinolysis), and microangiopathic hemolysis.

Management
Management of Kasabach–Merritt syndrome, particularly in severe cases, can be complex and require the joint effort of multiple subspecialists