Relative Echogenicity of Structures in the Pediatric Brain

After normalizing tissue to bone at the same depth, the relative echogenicity of brain structures can be determined. In order of decreasing echogenicity, they are: Choroid plexus > cerebellar vermis > > basal ganglia and periventricular area.

References

Padilla NF, Enriquez G, Jansson T, Gratacos E, Hernandez-Andrade E. Quantitative tissue echogenicity of the neonatal brain assessed by ultrasound imaging. Ultrasound Med Biol. 2009 Sep;35(9):1421-6.

Triceps Tendon Rupture

Triceps tendon rupture is uncommon and tends to occur in American football players and weight lifters. Olecranon bursitis, osteoarthritis, and steroid injections predispose patients to triceps tendon rupture. Most tears occur near the insertion site.

There is evidence of avulsion injury off the olecranon in 80% of cases. On MRI, the sagittal plane is best for delineating the extent of injury and differentiation partial from complete tears.

The lateral radiograph in this patient reveals posterior soft tissue swelling (white arrow) and bone fragments posteriorly (pink arrows), possibly corresponding to avulsion fragments. Sagittal MRI shows a tendon rupture with retraction from the olecranon (blue arrow). The location of the tendon corresponds roughly to where we saw some of the bone fragments on the lateral radiograph.

Reference

Chung CB. Chapter 11. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. pp454-455.

Types of Atrial Septal Defects

Atrial septal defects (ASDs) can be divided into four types based on location. From anterior to posterior, they are:

• Ostium primum atrial septal defect: Second most common type of ASD. Occurs in the lower septum. Associated with complete or partial mitral valve cleft and endocardial cushion defects.
• Ostium secundum atrial septal defect: Most common type of ASD. Occurs in the central septum. Patent foramen ovale is a variant. Not associated with endocardial cushion defects.
• Sinus venosus atrial septal defect: Involves the posterior atrial septum near the inferior or superior vena cava (mnemonic vena cava = venosus). May be associated with anomalous drainage of the pulmonary veins to the right atrium.
• Coronary sinus atrial septal defect: Least common type. The anatomy is important here. On its way to drain into the right atrium, the coronary sinus shares its roof with the posterior wall of the left atrium. Defects in the roof of the coronary sinus allow left atrial blood to be shunted into into the right atrium. For this reason, it is also known as an unroofed coronary sinus. Associated with a left superior vena cava (common) and heterotaxy syndromes.

Mesoblastic Nephroma

Mesoblastic nephroma (also known as fetal renal hamartoma or leiomyomatous hamartoma) is the most common neonatal renal tumor and the most frequent benign renal tumor in childhood. Up to 10% of all pediatric renal tumors are mesoblastic nephromas. While classified as benign, local invasion and hematogenous metastases may occur. Despite this tendency, the renal pelvis and vascular pedicle are spared. Additional complications have to do with mass effect and hormonal secretions that may result in polyuria, polyhydramnios in utero, gastrointestinal obstruction, and hypercalcemia.

Two types, the classic variant and the cellular variant, have been described. The cellular type tends to have a poorer prognosis and tends to affect children older than 3 months.

On ultrasound, we'll see a homogeneous echogenic mass arising from the kidney. The classic variant lesions may have a peripheral, hypoechoic, vascular ring on ultrasound or a large solid component, while cellular variant lesions tend to have cystic/necrotic change and central hemorrhage. The vascular ring is similar to those seen in thyroid lesions and represents dilated blood vessels at the periphery of the mass.

On CT, they present as a solid, nonenhancing renal mass with cystic or hemorrhagic components. No calcifications are seen. The collecting system may be enclosed by the mass, leading to apparent contrast excretion within the mass. The renal pelvis, however, is spared. Invasion of the vascular pedicle is also not seen.

T1-weighted images show a lesion with signal intensity characteristics similar to renal cortex and skeletal muscle. T1-weighted images show a hyperintense lesion. Minimal or no contrast-enhancement is seen within the mass, but classic variant lesions may have a peripheral, markedly enhancing ring that may correspond to the vascular ring seen on ultrasound.

The main differential consideration is congenital Wilms tumor. Unfortunately, imaging cannot differentiate the two and biopsy is required. Congenital adrenal neuroblastoma and multicystic dysplastic kidney may also be considered based on imaging findings.

References

• Lowe LH, Isuani BH, Heller RM, Stein SM, Johnson JE, Navarro OM, Hernanz-Schulman M. Pediatric renal masses: Wilms tumor and beyond. Radiographics. 2000 Nov-Dec;20(6):1585-603.
• Rieumont MJ, Whitman GJ. Mesoblastic nephroma. AJR Am J Roentgenol. 1994 Jan;162(1):76.
• Singh SP. Mesoblastic Nephroma. eMedicine. Oct 27, 2009.

Hypophosphatasia

Hypophosphatasia is a disease of low or absent serum alkaline phosphatase activity that results in incomplete ossification of cartilage and metaphyses and accumulation of unmineralized osteoid.

At least three types have been described:

• Neonatal: Diagnosed during the first week of life. Uniformly fatal.
• Infantile: Manifests by 6 months. Variable survival.
• Adult: Autosomal recessive.

Radiographically, there is decreased ossification of the skull and vertebrae. The decreased ossification of the skull may appear as isolated segments of thin bone or as a generalized boneless skull (caput membranaceum). Wormian bones may also be seen.

There are also poorly and irregularly ossified short tubular bones that are prone to bowing and fracture and may mimic osteogenesis imperfecta or other causes of florid rickets. Frayed and cupped metaphyses can also be seen.

The accumulation of unmineralized osteoid at the metaphyses is fairly specific and can help differentiate hypophosphatasia from osteogenesis imperfecta and other forms rickets.

References

• Glass RB, Fernbach SK, Norton KI, Choi PS, Naidich TP. The infant skull: a vault of information. Radiographics. 2004 Mar-Apr;24(2):507-22.
• States LJ. Imaging of metabolic bone disease and marrow disorders in children. Radiol Clin North Am. 2001 Jul;39(4):749-72. Review.

Cortical Tunneling

Cortical tunneling is the appearance of lucent striations within the cortex along the long axis of the bone. It can be seen as a normal variant (two or fewer in the metacarpal cortex) or in states of rapid bone turnover. Differential considerations include:

• Normal variant in children: High bone turnover.
• Hyperparathyroidism: Almost always associated with subperiosteal resorption.
• Hyperthyroidism:
• Reflex sympathetic dystrophy:
• Acromegaly: High bone turnover due to growth hormone
• Osteoporosis: Commonly seen in the endosteal zone of cortex with sparing of the periosteal cortex. The image shows a cases of cortical tunneling in the distal radius and ulna in a severely osteoporotic patient. When seen en face, the cortical lucencies can mimic medullary lesions.

A grading system for cortical tunneling was initially developed for the metacarpals and metatarsals by Meema and Schatz (1970). I've never heard anyone use this system, but here it is:

• Grade 0: No striation or only single marginal striation.
• Grade +: More marked marginal striation than that of grade 0 and/or minimal intracortical striation occupying less than half of the area under observation.
• Grade ++: Intracortical striae wider than that of grade + and occupying more than half of the area under observation.
• Grade +++: Marked intracortical striation throughout the entire bone.

References

• Genant HK, Kozin F, Bekerman C, McCarty DJ, Sims J. The reflex sympathetic dystrophy syndrome. A comprehensive analysis using fine-detail radiography, photon absorptiometry, and bone and joint scintigraphy. Radiology. 1975 Oct;117(1):21-32.
• Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease. 8th edition, page 559; Mosby (2004).
• Meema HE, Schatz DL. Simple radiologic demonstration of cortical bone loss in thyrotoxicosis. Radiology. 1970 Oct;97(1):9-15.
• Weiss C. Normal roentgen variant: cortical tunneling of the distal ulna. Radiology. 1980 Aug;136(2):294.

Castleman Disease of the Abdomen and Pelvis

Castleman disease is a rare, idiopathic disease characterized by atypical proliferation of lymphocytes. Although almost always benign, a rare, potentially fatal systemic form has been identified. Castleman disease may represent a response to chronic inflammation or a hamartoma of the lymph system, depending on who you believe.

It is most commonly found in the mediastinum (70% of case), but can be found in the neck (10%), pelvis (5%), or axilla (2%). It most commonly manifests as a localized mass or masses.

Three types have been defined histologically:

• Hyaline-vascular type: 90% of cases. 70% younger than 30. Usually asymptomatic
• Plasma cell type: 50% symptomatic (fever, elevated ESR, anemia, hypergammaglobulinemia, and splenomegaly).
• Mixed type.

Imaging findings in the mediastinum differ by histology, but all forms show enhancement. The hyaline-vascular type may present as a solitary, noninvasive mass; a dominant infiltrative mass with associated lymphadenopathy; or a matted lymphadenopathy without a dominant mass. The plasma cell type presents as a diffuse mediastinal lymphadenopathy.

In the pelvis the lesions may be located in the retroperitoneum, mesentery, porta hepatis, or pancreas. On imaging, there is a well-defined, focal enhancing mass that shows homogeneous contrast enhancement when small (< 5cm) or heterogeneous enhancement when large. Unlike mediastinal lesions, no difference is seen between the different types in the pelvis. A single case of an enhancing retroperitoneal mass with infiltration of the surrounding fat has been reported.

Calcifications may be seen in different patterns: Punctate, coarse, peripheral, or "arborizing."

Here we see a right lower quadrant mass, picked up on physical examination, seen on x-ray and further investigated by ultrasound and CT. The differential diagnosis of an enhancing retroperitineal mass such as this is:

• Lymphoma: Enlarged nodes bilaterally. Confluent soft tissue mantle of nodes surrounding aorta and inferior vena cava. Nodes may displace aorta from spine, unusual for other nodal mets
• Metastasis
• Infection: Abscess, tuberculosis.
• Sarcoma: Large RP mass with or without necrotic or cystic degeneration
• Schwannoma
• Paraganglioma
• Hemangiopericytoma
• Inflammatory pseudotumor: Heterogeneous mass. Nonenhancing, heterogeneous enhancement, or peripheral enhancement. May have central hypoattenuation due to necrosis in larger lesions. May have Central calcifications.
• Castleman

References