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Multicystic Dysplastic Kidney
Collection of variably-sized cysts that do NOT appear to communicate. no central dominant cyst
Most slowly decrease in size. Not sure if premalignant. Can cause HTN
Toxic synovitis
Dx of exclusion. Hip pain, limp, joint effusion but no organisms on tap. Ages 3-10. Sx improve with rest. Boys 4:1
? inflammation after viral infection.

Legg-Calve-Perthes Disease
idiopathic AVN of proximal femoral epiphysis. 
Early: Small femoral epiph, widened joint space and subchondral linear lucency. 
Late: Fragmentation of epiphysis, collapse, or areas of sclerosis and lucency.
Chronic: broad, overgrown femoral head, short femoral neck, physeal arrest.
Boys 4:1, whites, ages 5-8.
Slipped Capital femoral epiphysis
Idiopathic Salter 1 fracture through prox femoral physis with slippage of epiphysis (posterior and medial).
Boys 2.5:1, blacks, obese. Bilateral in 1/3. 
On frog leg: lateral metaphyseal line should intersect ossified epiphysis. SCFE=epiphsysis medial.
Usually pinned. Can get AVN.
Rickets
Caused by anything that decreases VitD or its effectiveness. Can't convert cartilage to mineralized osteoid, so build-up of nonossified osteoid.
Most evident at knees and wrists. metaphyseal fraying, cupping, irreg physis. Smudged trabecular markings.
Can get insuff fx ("Looser zones") and SCFE.
Lead poisoning
Broad scleoritc metaphyseal bands, often in growth areas like the knee. Some normal variant bands, so look for bands in ALL nearby metaphyses instead of just one. Normal tends to spare prox fibula
JRA
Seronegative, pauciarticular, large joints. (knee, ankle, wrist, hand, elbow, hip in order). 
x-rays may be normal or just effusion. Knee can show epiphyseal overgrowth, widened intercondylar notch, periosteal rxn. C-spine=ankylosis of apophyseal joints. Carpal bones= square and small, narrowing of joint spaces. Can later get erosions and ankylosis.
Many kids have splenomegaly or pleural effusion.
Hemophilia
Knee, elbow, ankle. Synovial hemosiderin deposition. Synovial hypertrophy with cartilage destruction. 
Chronic: epiphysial overgrowth. in knee, squaring of patella and wide intercondylar notch.
MRI: articular cartilage destruction, hypertrophied synovium (may be dark on T2 so looks similar to PVNS).
Anemia - sickle cell and thalassemia (effect on bones)
Marrow expansion, causing thinned cortex, coarse trabeculae, wide ribs, wide epiploic space in the skull ("hair-on-end", esp in thalassemia). 
Sickle cell: areas of infarct (sclerotic or lucent). Vert bodies have indented superior and inferior endplates ("lincoln log").
Any severe anemia can have gallstones, splenomegaly, extramed hematopoesis, OM. SS can autoinfarct spleen.
Radial dysplasia
Hypo- or aplasia of the radius. Often with first metatarsal or thumb too. 
Seen with VACTERL, Holt-Oram syndrome, Fanconi pancytopenia, and Thrombocytopenia with absense of radius syndrome.
Blount disease
Excessive medial bowing of the tibias, most common during infancy. Due to disturbance of growth in medial proximal tibial epiphysis. Irregularity, fragmentation and breaking of the medial tibial metaphysis.
Lung contusion
More common in kids due to compliant ribs.
CT characteristics: Non-segmental distribution, posterior location, crescenteric shape, mixed confluent and nodular. Kids can get a rim of non-opacified lung just under the ribs.
Laceration: as above, with fluid- or air-filled cyst in the opacified lung.
Middle mediastinal masses
Usually lympadenopathy or duplication cysts (bronchogenic, enteric or neurenteric).
Esophageal issues are also middle mediastinum: foreign body+erosion, achalasia, hiatal hernia.
Posterior mediastinal masses
Neuroblastoma until proven otherwise.
Additional list: neural crest tumors, neurofibromas, lateral meningocoele, diskitis, hematoma, extramedullary hematopoiesis.
Cyanotic congenital heart diseases
Tetralogy of Fallot
Transposition of the great arteries
Tricuspid atresia (and Ebstein's)
Total Anomalous Pulmonary Venous Return
Truncus arteriosus
Hypoplastic left heart
swyer-james syndrome
unilateral hyperlucent lung due to post-infectious bronchiolitis obliterans with air trapping. lung size is static, and has decreased pulmonary vessels.
infancy or childhood.
Non-cyanotic congenital heart diseases
Mostly left-to-right shunts: ASD, VSD, AVC, PDA. 
Obstructive lesions can cause failure: coarctation, aortic stenosis, pulmonary artery stenosis.
Patterns of tracheal/esophageal impression and associated vascular anomalies
Anterior trachea and posterior esophagus indentations = double aortic arch.
Anterior trachea, high in thorax = innominate artery.
Posterior esophagus = either left arch with aberrant right subclavian, or right arch with aberrant left subclavian.
Posterior trachea and anterior esophagus (ie something passing between them) = Pulmonary sling aka aberrant left pulmonary artery
Meconium aspiration syndrome
CXR: High lung volumes and ropy, perihilar, asymmetric opacities. Can have effusions.

Causes small airway obstruction and chemical pneumonitis. Pneumothorax in 20-40%.
Transient tachypnea of the newborn
More common in C-section due to lack of thoracic squeeze during delivery.  Peaks at 1 day, resolves by 2-3 days.

Similar appearance to pulmonary edema: airspace opacities, coarse interstitial markings, prominent/indistinct pulmonary vasculature, fissural fluid, effusions, cardiomegaly.
Neonatal pneumonia
Patchy, asymmetric perihilar densities and hyperinflation. May have effusions. 
Similar appearance to meconium aspiration syndrome.
Surfactant deficiency diseas/respiratory distress syndrome/hyaline membrane disease
Premature infants.

Low lung volumes, bilateral granular opacities, air bronchograms. If severe, can coalese to diffuse lung opacity. Pleural fluid very UNcommon
B-hemolytic strep neonatal pneumonia
Bilateral granular opacities and low lung volumes.

Identical to SDD. Presence of effusion favors pneumonia.
Pulmonary Interstitial Emphysema
Bubblelike or linear lucencies that can be focal or diffuse.

From mechanical ventilation perforating alveoli. Can appear similar to BPD, buts appears more abruptly and in the first weeks of life.
Serves as warning for complications such as pneumothorax
Bronchopulmonary dysplasia
Chronic lung disease of prematurity, usually after long time on vent.
By second week: hazy density throughout the lungs
Weeks to months: Coarse lung markings, bubblelike lucencies, asymmetric aeration
Finally: focal lucencies, coarse reticular densities, and bandlike opacities.
Differentials for Lucent and Solid lesions in neonates, respectively
Lucent:
Congenital lobar emphysema
CPAM
Pulmonary Interstitial Emphysema
Congenital diaphragmatic hernia

Solid:
Sequestration
Bronchogenic cyst
CPAM
Congenital lobar emphysema
Most to least common: LUL, RML, RLL

Hyperlucent, hyperexpanded lobe on CXR. May initially be soft tissuedensity due to fetal fluid, but becomes lucent. Paucity of pulmonary vessels.
Congenital Pulmonary Airway Malformation (formerly CCAM)
Cysts may be completely or partially fluid filled. May have cystic areas. Large lesions cause mass effect. These DO communicate w/ bronchial tree, so will fill with air within a few days of life.

Type 1:  Most common. 1 or more dominant cysts 2-10cm.
Type 2: Cysts <2cm. Assoc w/ renal agensis, sequestration, cardiac anomalies.
Type 3: Microcysts <5mm. Often involves entire lobe. Poorer prognosis.
Type 4: Unlined cyst.
Pulmonary sequestration
Abnormal pulmonary tissue that does not have a connection to the bronchial tree. 
Anomalous arterial supply via a systemic artery is characteristic.  
Extralobar have separate pleural covering.
Kids present w/ recurrent pneumonia.
Bronchogenic cyst
Due to abnormal budding of the tracheobronchial tree. Occur in mediastinum (65-90%) or lung parenchyma. Do not contain air except after infection. 
Due to middle mediastinal and perihilar location, often compress distal trachea or bronchi.
Viral pneumonia CXR findings
Pericronchial edema, coarse perihilar markings. 
The narrowed lumen and necroticdebris cause small airway occlusions, leading to areas of hyperinflation and subsegmental atelectasis.
Rounded pneumonia
Kids <8yrs. Most often Strep Pneumo. 
related to poor development of collateral ventilation pathways.
With cough and fever, treat with antibiotics and get repeat.
If rounded opacity in kid >8 yrs, think of other causes.
Common mediastinal masses by Ant/Middle/Post locations
Anterior:
Normal thymus
Lymphoma
Teratoma
(Thymoma, thyroid enlargment much less common)

Middle:
Lymphadenopathy
Duplication cyst (bronchogenic, enteric, or neurenteric)

Posterior:
Neuroblastoma
Pediatric chest wall masses
Ewing sarcoma, Askin tumor (PNET of the chest wall), other sarcomas.
Necrotizing enterocolitis
Premies in the NICU. 1-3 weeks after birth. Mostly ileum and right colon. Treated with Abx and NPO.

Suggestive findings: focal bowel dilation, unchanging gas pattern over several films. (ie focal ileus)
Definitive: pneumatosis.

Free air is the only absolute indication for surgery.
Common causes of intestinal obstruction in neonates, divided into High and Low
High obstruction:
Midgut volvulus/malrotation
Duodenal atresia/stenosis
Duodenal web
Annular pancreas
Jejunal atresia

Low:
Hirschsprung
Meconium plug syndrome (small left colon)
Ileal atresia
Meconium ileus
Anal atresia
Malrotation and midgut volvulus on UGI
Normal bowel must have the duodeno-jejunal junction 1) to the left of the spine and 2) at the same level or superior to the duodenal bulb.

Midgut volvulus: Twisting of the small bowel around the SMA axis. Findings on UGI: Corkscrew duodenum and proximal jejunum, or duodenal obstruction. 90% present by 3 months. 

Bilious vomitting + malrotation = surgical emergency.
Microcolon differential on enema on infant
If collapsed TI with dilated proximal small bowel loops: ileal atresia

If TI distended with multiple filling defects: Meconium ileus. (Exclusively in CF patients)
Hirschsprung disease
Denervated colon segment spasms and causes functional obstruction. Affected portion small in caliber, while normal proximal colon is dilated. No skips lesions. Rectum should have largest diameter of colon in normal kids.
Boys 4:1.
Meconium plug syndrome (aka small left colon)
Functional immaturity of ganglion cells. Temporary. 
Multiple filling defects in the colon. Right and transverse colon may be larger than left colon.
Enema therapeutic.
Meconium peritonitis
In utero perforation of bowel due to bowel atresia, volvulus, or meconium ileus.

Findings: bowel obstruction, peritoneal calcifications, meconium cysts in peritoneal cavity.
GI duplication cysts
Cystic structures with bowel wall signature (hypoechoic external rim, hyperechoic internal rim). Typically do not communicate with bowel lumen. Most commonly at TI or distal esophagus. Usually present in first year of life.
Biliary atresia
Congenital obstruction of biliary system. Duct proliferation intrahepatically, absense of extrahepatic ducts. Needs corrective surgery before cirrhosis. 
Associated with abdominal heterotaxy syndromes such as polysplenia and Trisomy 18.
Absense of GB on US is suggestive.
HIDA shows tracer taken up in liver, but never reaches GI tract.
Hepatoblastoma
Most common primary liver tumor of childhood. High AFP levels. Risk factors: Beckwith-Wiedemann, hemihypertrophy,  FAP, Gardner, Wilms tumor, biliary atresia. 
Well-defined, tend to displace rather than invade adjacent structures.
Prune Belly Syndrome (Eagle-Barrett)
Triad of abdominal muscle hypoplasia, cryptorchidism, and urinary tract abnormalities. 
UG abnormalities include: severe BL hydro, hypertrophied bladder, urachal diverticulum, hydroureter.
ARPKD
Diffuse enlargement of the kidneys on US with increased echogenicity. Cysts are so small, you may not see any. 
Liver shows diffuse echogenicity related to fibrosis; may go on to cirrhosis.
Wilms tumor
Most common peds renal malignancy. 8% of all peds malignant tumors.  Peak at 3 yrs. Assoc w/ hemihypertrophy, Beckwith-Wiedemann, others. Bilateral in 5%. 
Large mass arising from the kidney, typically inc echogenicity. May have areas of hemorrhage, necrosis, calcification. Can invade renal veins/IVC.  Mets to lung and liver. Tends to displace vessels rather than encase like neuroblastoma.
Neuroblastoma
Malignant tumor of primitive neural crest cells. Usually adrenal, but can come from anywhere on sympathetic chain.  Tends to invade adjacent tissues. 90% have elevated catecholamines in urine. 
Prognosis depends on age. Young kids = better prognosis. Mets to liver and skin. >1yr, goes to bone; worse prognosis.
on CT: Lobulated; infiltrative growth. Surrounds and engulfs vessels. Often have hemorrhage, necrosis, calcifications (85%). T2 bright.
Pelvic rhabdomyosarcoma
Most common malignant sarcoma of childhood. Usually found during first 3 yrs.  Most commonly pelvis and GU tract, then head and neck. 
In bladder, multilobulated mass like a bunch of grapes.
Common sites of avulsions in adolescents (pelvis)
The pelvis is the most common location for avulsions.
Iliac crest - transversalis, internal and external obliques
Anterior superior iliac spine - sartorius
Anteroinferior iliac spine - rectus femoris
Ischial apophysis - biceps femoris, gracilis, semimembranous, semitendinous.
Lesser trochanter - iliopsoas.
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