A Rare Case of <i>Rhizomucor pusillus</i> Infection in a 3-Year-Old Child with Acute Lymphoblastic Leukemia, Presenting with Lung and Brain Abscesses—Case Report

Invasive <i>Mucormycosis (IM)</i> is an extremely rare infection with a high mortality rate, caused by a group of fungi classified as <i>Mucorales</i> moulds. <i>Rhizomucor pusillus</i> is a saprophitic, thermophilic, and angioinvasive microorganism that grows and lives at about 45 °C and is usually found in different environmental spaces such as soil, air, water, food, and other organic matter. These features predispose the infection to wide dissemination, especially in immunocompromised patients and most often in children after chemotherapy for hematological malignancies (HMs). <i>Mucormycosis</i> in patients with hematologic malignancies and neutropenia represents between 0.07% and 4.29% of the concomitant diseases. <i>IM</i> can develop into an infection in different sites, but its most common manifestation is pulmonary, followed by rhino-orbital–cerebral and disseminated forms. In recent years, an increased morbidity rate has been associated with the ongoing <i>COVID-19</i> pandemic, as cited in the literature. There are many publications with <i>COVID-19-associated mucormycosis</i> (CAM) cases. The present treatment protocol includes extensive and radical surgical debridement and systemic antifungal therapy with Liposomal Amphotericin B (L-AmB), Posaconazole, and Isavuconazole, either combined or as monotherapy. Despite these new treatment modalities, the mortality rate remains over 50%. We present a rare case of a 3-year-old child with acute lymphoblastic leukemia (ALL) and systemic <i>Rhizomucor pusillus</i> infection, diagnosed on the occasion of lung and brain abscesses. The patient underwent lung and brain surgery and is recovering well with no further complications. The two-year follow-up period shows no signs of recurrence of the disease.