Tumor pathology
Congenital Mesoblastic nephroma is a malignant tumorous growth of the kidneys mesenchyme (i.e. connective tissue cells). Histologic examination of these tumors provides critical information on their prognoses. This examination divides congenital mesoblastic nephroma into three types:

1) The classic type occurs in ~39% of patients. Its tissues show interlaced spindle-shaped smooth muscle cells evidencing low mitotic activity with no evidence of tumor encapsulation; and infiltration into and entrapment of normal kidney tissue. 2) The cellular type occurs in ~42% of patients. Its tissues show densely packed fibrosarcoma-like cells evidencing high rates of mitosis, less infiltration of normal kidney tissue, and multiple areas of hemorrhage and cysts. 3) The mixed type occurs in ~19% of patients. It shows a mixture of the classic and cellular types in different areas of the neoplasm. Genetics
A study conducted in 1998 found that congenital mesoblastic nephroma tissues taken from some patients contained an acquired mutation, the ETV6-NTRK3 fusion gene. This gene results from a translocation of genetic material from the ETV6 gene located on the short arm (designated p) of chromosome 12 at position p13.2 (i.e. 12p13.2) to the NTRK3 gene located on the long arm (designated q) of chromosome 15 at position q25.3 (i.e. 15q25.3). This ETV6-NTRK3 gene fusion is notated as t(12;15)(p13;q25) and consists of the 5 end of ETV6 fused to the 3 end  of NTRK3. In consequence, the chimeric protein product of this gene lacks ETV6 proteins transcription factor activity while having NTRK3 proteins tyrosine kinase in an unregulated and continuously active form.
Whether an effusion causes tamponade depends on the amount of fluid and how long it took to accumulate. When fluid collects slowly, the pericardium can stretch. Thus, a chronic effusion can be as large as 1 liter. Acute effusions can cause tamponade when small because the tissue does not have time to stretch. Diagnosis
Rapid evaluation of shock is essential given its life-threatening nature. Diagnosis requires a thorough history, physical exam, and additional tests. One must also consider the possibility of multiple types of shock being present. For example, a trauma patient may be hypovolemic from blood loss. This patient could also have tension pneumothorax due to trauma to the chest.Vital signs in obstructive shock may show hypotension, tachycardia, and/or hypoxia. A physical exam include be thorough, including jugular vein exam, cardiac and lung exams, and assessing skin tone and temperature. Response to fluids may aid in diagnosis. Labs including a metabolic panel can assess electrolytes and kidney and liver function. Lactic acid rises due to poor tissue perfusion. This may even be an initial sign of shock and rise before blood pressure decreases. Lactic acid should lower with appropriate treatment of shock. EKG should also be performed. Tachycardia is often present, but other specific findings may be present based on the underlying cause.At the bedside, point-of-care echocardiography should be used. This is non-invasive and can help diagnose the four types of shock. Echocardiography can look for ventricular dysfunction, effusions, or valve dysfunction. Measurement of the vena cava during the breathing cycle can help assess volume status.