New T-cell acute lymphoblastic leukemia with hyperleukocytosis, tumor lysis, and a mediastinal mass

There are three parallel emergencies: the mediastinal mass with airway compromise, hyperleukocytosis with risk of leukostasis, and established tumor lysis with acute kidney injury and hyperkalemia. The potassium of 6.1 mmol/L with a rising creatinine is the most immediately lethal problem. Obtain an ECG, place on continuous cardiac monitoring, stop all potassium and phosphate intake, and treat hyperkalemia with calcium gluconate for membrane stabilization if there are ECG changes, insulin with glucose, and a beta-agonist; loop diuretics depend on volume status. Urgent nephrology involvement is needed because dialysis may be required for refractory hyperkalemia or oliguric renal failure.

Start intravenous hydration at roughly 2–3 L/m²/day unless oliguric, and give rasburicase or allopurinol as discussed below. Avoid supine positioning and sedation. Transfuse red cells cautiously if symptomatic, and transfuse platelets if bleeding or before procedures. Do not start steroids or chemotherapy until a diagnostic sample is obtained unless airway compromise forces it; call anesthesia and critical care early.

This child has high-risk tumor lysis: hyperuricemia, hyperphosphatemia, hypocalcemia, hyperkalemia, and renal insufficiency. Rasburicase is the most effective urate-lowering agent and is generally preferred in this setting because it rapidly degrades uric acid. However, it is contraindicated in G6PD deficiency because it can cause severe hemolysis and methemoglobinemia. G6PD testing should be sent immediately, but results may take hours to days, and recent transfusion can confound interpretation.

In a boy with severe established tumor lysis, many centers give rasburicase while awaiting G6PD results because the risk of untreated hyperuricemia and renal failure is immediate, then stop if deficiency is confirmed. An alternative is allopurinol plus aggressive hydration and dialysis backup, accepting slower urate control. Rasburicase samples must be transported on ice and analyzed promptly because uric acid continues to degrade ex vivo. Do not use rasburicase if G6PD deficiency is known. Whichever agent is chosen, monitor electrolytes every 6–8 hours and treat symptomatic hypocalcemia cautiously; avoid calcium if phosphate is very high unless there is tetany or seizures.

With 92% blasts in the peripheral blood, flow cytometry on a peripheral sample may establish the diagnosis without exposing the child to general anesthesia. Send urgently for flow cytometry, cytogenetics, and molecular studies. A bone marrow aspirate is usually needed for comprehensive risk stratification, but it can often be performed with minimal sedation and should be coordinated with anesthesia and critical care. If a tissue diagnosis is essential, consider a lymph node biopsy under local anesthesia rather than a mediastinal biopsy. General anesthesia and supine positioning are hazardous with a 9 cm anterior mediastinal mass and 40% tracheal narrowing; if anesthesia is unavoidable, involve a senior anesthesiologist and prepare for airway rescue, including availability of extracorporeal support.

Pre-phase steroids can shrink the mass and relieve airway compromise, but they can obscure the diagnosis and reduce the yield of marrow and flow studies. The usual sequence is to obtain diagnostic samples first, then start steroids as part of definitive therapy. If the child develops stridor, severe desaturation, or cannot lie flat, steroids may be justified immediately after a peripheral blood sample is sent. Document the rationale and involve the family in the decision.