Acute disseminated encephalomyelitis (ADEM) and brain abscess, both with lesions in brain, sometimes show only subtle neurological symptoms resulting in delayed diagnosis. Fever of unknown origin with nonspecific neurological or psychiatric symptoms such as headache or irritability should prompt us to perform imaging study such as magnetic resonance imaging (MRI) or contrast enhanced computed tomography on suspicion of either of the above-mentioned diagnoses.

Scull base osteomyelitis is difficult to diagnose because of inconspicuous focal symptoms and imaging findings. To diagnose it correctly, imaging study should include nuclear medicine scan as needed in addition to MRI scan.

Sjögren’s syndrome in children often shows scant symptoms of dry eyes and dry mouth. Imaging studies such as sialography, MR sialography and salivary scintigraphy may reveal subclinical lesions in salivary glands and are important for making the diagnosis.

Fever of unknown origin (FUO) is categorized into four etiological groups: infections, neoplasms, non-infectious inflammatory diseases, and miscellaneous conditions. We often have difficulties in diagnosing prolonged fever in our daily medical practice. Prolonged fever involving the neck also consists of these etiological categories, and the diagnosis is confirmed with a detailed clinical history, physical examination and some appropriate tests including imaging studies. This paper focuses on diagnostic imaging of the neck associated with prolonged fever, and shows typical images of representative diseases, such as various types of abscess, malignant lymphoma and Kawasaki disease. Diagnostic imaging may lead to the accurate diagnosis, and provide essential information for proper treatment.

Acute undifferentiated febrile illness (AUFI) is frequently encountered in pediatric care. Because the etiologies of AUFI are various and the clinical presentations are similar among them, the differential diagnosis is difficult. Urinary tract infection is one cause of AUFI and the most common bacterial infection in children, especially those under 2 years of age. The diagnosis is very important as it may be a marker for vesicoureteral reflux and congenital anomalies of the kidney and urinary tract. Moreover urinary tract infections are sometimes associated with life-threating sepsis. However the precise diagnosis is often difficult, because signs and symptoms are non-specific. In this section, I describe the imaging approach to urinary tract infections to achieve better diagnosis and treatment.

There are many causes of pediatric fever of unknown origin: infectious, autoimmune, oncologic, neurologic, genetic, factitious, and iatrogenic. More common and clinically significant diseases will be reviewed in this article: pyogenic osteomyelitis, sacroiliitis, leukemia, metastatic neuroblastoma, and juvenile idiopathic arthritis (JIA).

Their clinical manifestations or diagnostic images sometimes overlap. The role of radiograph and computed tomography (CT) for the early diagnosis of musculoskeletal diseases is limited. Magnetic resonance imaging (MRI) is the best modality for early detection of abnormalities of bone marrow, adjacent joint and soft tissue. MRI with gadolinium administration is often effective for evaluating the spread and activity of the inflammation. Ultrasound is also a supportive modality for evaluating soft tissue swelling, subperiosteal abscess, joint effusion, and synovial hypervascularity. It must be kept in mind that abnormal intensities of bone marrow can be diffusely recognized in hematopoietic malignancies such as leukemia and metastatic neuroblastoma in contrast to the other musculoskeletal diseases (osteomyelitis, sacroiliitis, JIA).

It is important to diagnose and begin treatment as soon as possible because delayed diagnosis of these musculoskeletal diseases can cause growth disturbance and bone deformity, For this reason, it is essential to identify the best diagnostic approach and the characteristics of their diagnostic images.

Wandering spleen is a very rare entity, and a cause of splenic infarction. Splenic infarction presents acute abdomen and requires emergent surgery occasionally. Thus, early diagnosis is very important as soon as possible. A 14-year-old boy presented with fever and abdominal pain for 4 days, and was admitted to our hospital. At first, we detected a loss of splenic artery flow to the spleen and a large spleen by abdominal ultrasonography. Next, we suspected splenic infarction by finding non-enhancing areas in the whole spleen by abdominal enhanced CT. Additionally, we could correctly diagnose torsion of wandering spleen by finding whirl sign of twisting of splenic vessels with abdominal dynamic CT. After a diagnosis, conservative treatment, not but surgical treatment, led to improvement of symptoms and loss of splenic artery flow by torsion of the wandering spleen. Therefore, we considered that his spleen had shown transient ischemic change by torsion of the wandering spleen. We reported that abdominal dynamic CT is clinically useful for identification of torsion of wandering spleen, and the patient was a rare case that improved with conservative treatment.

We report a case of an interhemispheric cyst complicated by subdural hematoma in a 16-year-old boy. He was diagnosed with a right interhemispheric cyst on magnetic resonance imaging (MRI) of the head during examination for an afebrile seizure at 14 years of age. Approximately one year later, a head MRI was performed to investigate the cause of headaches. The interhemispheric cyst was found to have decreased in size, but subdural effusion continuing from the cyst at the right convexity was observed. Two months later, following a severe headache, a head MRI showed hemorrhage at the place of effusion in the subdural space. Additionally, displacement of the brain parenchyma was observed. Emergent drainage of the subdural hematoma was performed, and the patient was diagnosed with chronic subdural hematoma. In this case, the head MR images taken over time showed the development of subdural effusion from the interhemispheric cyst, followed by the development of a subdural hematoma. Slight trauma is known to cause subdural hematoma in patients with arachnoid cysts; upon diagnosis, it is important to inform patients of the precautions to prevent an increase in intracranial pressure and response to the symptoms of increasing intracranial pressure.

A 14-year-old boy with epigastralgia was diagnosed with acute pancreatitis based on elevated levels of pancreatic amylase (225 IU/L) and lipase (677 IU/L), enlargement of the pancreatic tail, and increased density of the surrounding adipose tissue on computed tomography (CT) imaging. A 1.5-cm tumor was found that appeared as a low-absorption area on early-phase CT images, with increased intensity on late-phase images. Heavily T2-weighted magnetic resonance imaging (MRI) suggested that the tumor had triggered pancreatitis by displacing the main pancreatic duct. From these imaging findings, we suspected a solid pseudopapillary neoplasm (SPN). Fluid replacement and protease inhibitor therapy for pancreatitis were successful. Tumorectomy was performed 1 month after the onset of epigastralgia, and the diagnosis of SPN was confirmed based on the histological findings. Proactive use of diagnostic imaging is recommended for identifying the cause of acute pancreatitis. Because SPN is a possible cause, diagnostic images should be thoroughly examined for size, location, internal characteristics, capsule formation, calcification, relationship to the main pancreatic duct, and extent of invasion of the tumor, especially in pediatric cases.

Fibrodysplasia Ossificans Progressiva (FOP) is a disease that begins in infancy and is characterized by progressive ossification of skeletal muscles throughout the body. Stimuli such as injury and infection can trigger flare-ups involving subcutaneous mass formation, resulting in subsequent ossification at the site. Imaging diagnosis is often difficult in the initial phase where only a mass due to flare-up is present. In most cases, the diagnosis is made only after ossification has occurred, typically several years after the onset. Herein, we report a case of FOP diagnosed 4 months after onset. Careful imaging evaluation of the mass showed characteristics of FOP distinct from those of malignant tumors and other mass-forming lesions. Since early intervention can improve the outcome for patients with FOP, early diagnosis through careful imaging evaluation and awareness of the disease is important.