Childhood malignant tumors are said to be extremely rare, but they are always ranked within the top 3 causes of death in childhood. It is thus desirable for us to have basic knowledge of childhood tumors roughly. We reviewed the overview of childhood tumors in every region with a little relaxation. The basic knowledge of major tumors and useful imaging findings were discussed.

Childhood cancers are very rare and differ from adult cancers in the way they grow and spread. Therefore treatment strategies should be established by nation-wide multi-center trials. The Japan Children’s Cancer Group (JCCG) was founded to research how they are treated.

The radiologists of each institution may have very few chances to diagnosis and treat childhood cancers; therefore JCCG have introduced the Central Radiological Diagnosis System in which specialized radiologists can discuss the diagnosis of childhood cancer via the internet.

Radiology plays critical roles in cancer diagnosis and treatment in the various points during the treatment of pediatric cancer; not only the diagnosis of the tumor but clinical staging is important to select the protocol for treatment. After chemotherapy, evaluation of the effects of anti-cancer drugs is necessary. Before tumor resection, imaging studies provide various critical information to the surgeon to perform the operation. Therefore close interaction between the radiologists and pediatric oncologists, surgeon and pathologists is important in the treatment of pediatric cancers.

Pediatric post-mortem imaging is used for many purposes, including determining the cause of death, assessing the true pathological condition, confirmation of medical procedures, and identifying child abuse. Post-mortem magnetic resonance (PMMR) has recently been reported to have higher diagnostic accuracy for congenital anomalies compared to post-mortem computed tomography (PMCT). However, more expensive MRI is rarely performed because its cost is hospital-borne in Japan. PMCT is a more commonly used method and may be a feasible and significant tool to detect abuse leading to death in sudden unexpected infant death cases.

Artificial intelligence has been through two booms so far and is said to be reaching its third boom. What is the current state of artificial intelligence and machine learning related research in the pediatric field? More than 400 papers were searched by keywords such as artificial intelligence, machine learning and pediatric. By classifying these according to purpose, machine learning method, image method, result, we investigated the tidal current to the present and determined the latest trends.

Wilms tumor is the most common pediatric renal mass, while congenital mesoblastic nephroma (CMN) is the most common renal tumor in neonates and infants under 6 months. We report a 2-month-old male with CMN. His chief symptom was persistent crying. Abdominal ultrasonography revealed a mass of 7 centimeters in diameter on the upper pole of the right kidney, but did not detect the right adrenal grand. Laboratory examinations revealed that his neuron-specific enolase (NSE) level was elevated, and thus neuroblastoma was tentatively diagnosed. However, MRI and CT revealed it was a renal tumor. An NSE-producing Wilms tumor was suspected, but CMN was diagnosed considering his age and radiographic characteristics. The tumor was completely resected with unilateral nephrectomy. Histological examination confirmed a diagnosis of cellular-type CMN with EVT6-NTRK3 gene fusion. Adjuvant therapy was not administered because the surgical margin was pathologically negative and no residual uptake was detected in whole-body PET-CT. An onset age ≥3 months and cellular-type CMN at stage III are risk factors for relapse; therefore, adjuvant therapy was previously recommended. However, recent reports demonstrated that patients with cellular-type CMN and ETV6-NTRK3 translocation have a good prognosis. CMN is rare and further studies are expected.

Kawasaki disease is an idiopathic acute febrile illness prevalent among infants that primarily leads to small- and medium-sized arterial vasculitis. Reports on patients with Kawasaki disease and contrast neck CT showing retropharyngeal low-density area compatible with edema have surfaced. We described a case of a four-year-old boy with Kawasaki disease. On admission, he complained of severe neck pain and showed neck movement range limitations. We discovered retropharyngeal space and left para-pharyngeal low-density areas (the latter accompanied with peripheral enhancement) on the first contrast CT scan of his neck. We suspected retropharyngeal edema because of Kawasaki disease and a para-pharyngeal abscess. The retropharyngeal edema disappeared after IVIG and antibiotics therapy. On the contrary, the para-pharyngeal abscess shrank slightly but did not disappear. We continued with intravenous antibiotic therapy, and the neck pain and rigidity improved gradually. On the 19th day after admission, a third CT of the neck demonstrated disappearance of the abscess. On the 48th hospital day, we discharged the patient without any coronary artery sequelae.

Differentiating a spinal epidural fluid collection from a spinal epidural hematoma following a lumbar puncture is difficult due to the similarity of their physical findings. However, the respective neurological prognosis and therapeutic strategy differ. Herein we presented the case of a 2-year-old male patient with a spinal epidural fluid collection following a lumbar puncture. Ultrasonography showed a highly echoic area in his spinal canal suggesting a spinal hematoma. Magnetic resonance imaging revealed areas of iso-signal intensity surrounding the thecal sac, abnormal narrowing of the subarachnoid space in the cauda equina, and a heterogeneous signal in the epidural fat. Based on these findings, spinal epidural fluid collection was diagnosed. Appropriate use of ultrasonography and MR imaging can facilitate the diagnosis of spinal epidural fluid collection.