Sunday, May 31, 2009

The Ascending Lumbar Communicant Vein

The ascending lumbar communicant vein is a communication between the left ascending lumbar vein and the left renal vein. Because of its retroperitoneal location, when dilated, it may be mistaken for a lymph node on non-contrast studies with thick collimation.

The image shows the left renal vein in yellow, the ascending lumbar communicant vein in red, and the lumbar vein in blue.

References

Yao Y, et al. Communicating Vein between the Left Renal Vein and Left Ascending Lumber Vein: Incidence and Significance on Abdominal CT. Radiation Medicine: 2003; 21(6) 252–257.

Saturday, May 30, 2009

Benign Extra-Axial Fluid

Benign extra-axial fluid, previously known as idiopathic external hydrocephalus, is rapid head growth in neonates accompanied by increased fluid in the subarachnoid space.

It is detected typically between ages 3 and 8 months. The condition is self-limited with resolution of subarachnoid space enlargement by 2 years of age. Any developmental delay also resolves as the extra fluid resolves. The macrocephaly, however, usually persists. A family history of benign macrocephaly is also commonly seen.

Mild hydrocephalus is seen in 2/3 of patients. Grayscale ultrasound findings include sulcal dilatation with normal gyrus configuration. The cortical vein sign, initially described on MRI, can help differentiate subarachnoid fluid (seen in passive dilatation and benign extra-axial fluid) from subdural fluid (seen in trauma). Visualization of cortical veins within fluid collections localizes the collection to the subarachnoid space, making a subdural collection less likely.

Differential considerations include:
  • Passive dilatation of the subarachnoid space due to brain atrophy
  • Acquired extraventricular obstructive hydrocephalus
  • Different stages of subdural hematoma, for example from nonaccidental trauma

References

Friday, May 29, 2009

Monitoring for Fetal Anemia

An Rh-positive fetus in a sensitized mother should be monitored for fetal anemia. Serial amniocentesis for evaluation of bilirubin (the Delta OD450) can be used to quantify fetal hemolysis.

Ultrasound can also be used by measuring the the peak systolic velocity (PSV) of the middle cerebral artery (MCA). Serial measures of MCA PSV are plotted as a function of gestational age and compared to control values.

Mari et al (2000) plotted the PSV of the MCA of fetuses with no anemia or mild anemia (open circles), moderate or severe anemia (triangles), and those with hydrops (solid circles). They found that fetuses with moderate or severe anemia had PSVs values greater than 1.50 times the median (dotted curve).

References

Mari G et al. Non-invasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization. N Engl J Med 2000;342:9–14.

Thursday, May 28, 2009

Cecal Volvulus and Bascule

A cecal bascule is a variant of cecal volvulus that is thought to result from anteromedial folding of the cecum in relation to the ascending colon without torsion. Cecal volvulus can occur due to clockwise or counterclockwise twisting of the cecum along its axis, in which case it ends up in the right lower quadrant. Cecal volvulus may also result from twisting and inversion of the ceccum, in which case it ends up in the left upper quadrant.

Wednesday, May 27, 2009

Chemical Shift Imaging of the Liver

Chemical shift imaging imaging is used for the detection of microscopic fat, whereas fat suppression techniques affect macroscopic fat.

Lesions with microscopic fat include:
  • Focal or diffuse hepatic steatosis
  • Hepatic adenoma
  • Hepatic lipoma
  • Well-differentiated hepatocellular carcinoma
  • Hepatic angiomyolipoma
  • Metastatic germ cell tumor
  • Adrenal adenoma
  • Renal cell carcinoma

Tuesday, May 26, 2009

Cystic Hygromas and Webbed Necks

A cystic hygroma ("moist tumor") is thought to form because of absent or delayed formation of lymphatico-venous connections, leading to lymphatic enlargement at the neck. The nuchal translucency is thought to represent a small cystic hygroma.

It is thought that delayed communication between the lymphatic and venous systems accounts for the resolution of cystic hygromas in some fetuses. In addition, some believe that the webbed neck and high hairline seen in patients with Turner syndrome are the sequella of resolved cystic hygromas.

References

Cystic Hygroma by Sabih D and Khan AN. eMedicine. Jul 17, 2008.

Monday, May 25, 2009

Ultrasound Dropout in in utero Detection of Septal Defects

Due to limited lateral resolution, an apical 4-chamber view of the heart may give the appearance of a ventricular or atrial septal defect if the septum is parallel to the ultrasound beam. A subcostal view should be obtained to determine if the VSD or ASD is real.

References

Chaoui R. Anomalies and Diseases of the Fetal Heart. In Eberhard Merz (Ed.), Ultrasound in obstetrics and gynecology. Georg Thieme Verlag. 2004.

Sunday, May 24, 2009

Meckel-Gruber Syndrome

Meckel-Gruber syndrome is an autosomal recessive disease characterized by the triad of multicystic dysplastic kidneys (>95%), encephalocele (>60%), and postaxial polydactyly (>50%).

On prenatal ultrasound, there are multicystic dysplastic kidneys: Enlarged, echogenic kidneys with or without macroscopic cysts. There is associated oligohydramnios and a small or absent bladder due to poor renal function. An encephalocele is seen in more than 60% of cases. The fetus may also have postaxial polydactyly that usually affects all four extremities, but this may be hard to detect due to the oligohydramnios.

Hepatic fibrosis is seen at autopsy, but is usually difficult to appreciate on prenatal ultrasound.

As an autosomal recessive syndrome, this is an important association to recognize on prenatal ultrasound, as it will affect counseling for the parents regarding subsequent pregnancies.

Saturday, May 23, 2009

Classification of Polydactyly and Polysyndactyly

Polydactyly is the most common congenital hand anomaly, seen in approximately 1:700 pregnancies. It's classified according to the side of the hand or foot in which the extra digits arise.

Post-axial (most common): Extra digit(s) on the small finger or 5th toe side.
Central (least common): Middle three digits are involved
Pre-axial: Extra digit(s) on the thumb or great toe side

An extra digit consisting of soft-tissue without bone is usually an isolated finding without associated anomalies. An extra digit with bone is more likely to be associated with other anomalies. An autosomal dominant pattern of transmission is also associated with a favorable prognosis.

Post-axial polydactyly may also be associated with trisomy 13, Meckel-Gruber syndrome, Bardet-Biedl syndrome, Smith-Lemli-Opitz syndrome, short ribs–polydactyly syndromes, and Ellis-van Creveld syndrome.

Pre-axial and central polydactyly are more often associated with syndromes. Pre-axial polydactyly has been associated with Holt-Oram syndrome, short ribs–polydactyly syndromes, Carpenter syndrome, trisomy 21, VACTERL, and Fanconi anemia.

References

Rypens F et al. Obstetric US: Watch the Fetal Hands. RadioGraphics 2006; 26: 811-829.

Friday, May 22, 2009

Fetal Gallstones

Gallstones and hepatic masses are in the differential diagnosis of echogenic foci in the right upper quadrant. Gallstones and sludge may be seen during the third trimester, and are thought to be caused by hemolytic disease, cholestasis, and maternal drug use. Fetal gallstones and sludge are not generally associated with postnatal complications, and most resolve by birth or soon thereafter.

References

McNamara A and Levine D. Intraabdominal Fetal Echogenic Masses: A Practical Guide to Diagnosis and Management. RadioGraphics 2005;25:633-645.

Thursday, May 21, 2009

Jarcho-Levin Syndrome

Also known as spondylocostal dysostosis, Jarcho-Levin syndrome is characterized by vertebral anomalies (hemivertebrae, fused vertebrae) and asymmetry of rib fusions.

Prenatal ultrasound shows spinal disorganization associated with abnormal chest configuration and normal lengths of long bones.

Jarcho-Levin syndrome can be differentiated from asphyxiating thoracic (Jeune) dystrophy (acromelic dwarfism with short ribs and normal spine) and thanatophoric dysplasia (rhizomelic dwarfism with short ribs and platyspondyly). In contrast to these two entities, the limbs in Jarcho-Levin syndrome are normal.

Update

More recently, Jarcho-Levin syndrome (spondylocostal dysostosis) has been differentiated from Lavy-Moseley syndrome (spondylothoracic dysostosis). These two entities have previously been confused with each other, with Lavy-Moseley syndrome suggested as a subtype of Jarcho-Levin syndrome.

Jarcho-Levin syndrome is a panethnic disorder characterized by asymmetry of rib fusions; fused, block and hemi vertebra; and a high rate of mild congenital scoliosis. The thoracic insufficiency and respiratory deficiency are less severe when compared to Lavy-Moseley syndrome, but respiratory compromise and infection remain serious concerns in affected individuals.

Jarcho-Levin syndrome usually follows an autosomal-recessive pattern of inheritance, but some families with an autosomal dominant pattern have been reported.

Lavy-Moseley syndrome, in contrast, is more commonly reported in patients with Puerto Rican ancestry and is characterized by fusion of the thoracic spine; posterior fusion of the ribs with the thoracic spine, creating a fan-like or "crab" configuration; and fusion of the entire cervical spine, with the occiput of the skull fused to C1. Mild scoliosis may uncommonly be present. In contrast to Jarcho-Levin syndrome, there is severe respiratory compromise due to the markedly shortened thorax.

The inheritance pattern of Lavy-Moseley syndrome is less well-understood.

References

Berdon WE, Lampl BS, Cornier AS, Ramirez N, Turnpenny PD, Vitale MG, Seimon LP, Cowles RA. Clinical and radiological distinction between spondylothoracic dysostosis (Lavy-Moseley syndrome) and spondylocostal dysostosis (Jarcho-Levin syndrome). Pediatr Radiol. 2011 Mar;41(3):384-8.

Wednesday, May 20, 2009

Achondrogenesis

Achondrogenesis is a type of osteochondrodysplasia, an intrinsic abnormality of cartilage and/or bone formation. Achondrogenesis is characterized by normal or poor mineralization of the skull, poor or absent mineralization of the spine, severe pulmonary hypoplasia, micromelia, and abnormalities of the pelvis. Two types of achondrogenesis have been described. Type I achondrogenesis is further divided into subtypes A and B.

  Type IA
(Houston-Harris)
Type IB
(Parenti-Fraccaro)
Type II
(Langer-Saldino)
Skull Large
Poorly ossified
Large
Normal ossification
Mandible Micrognathia
Spine Completely unossified Pedicles may be ossified Poor ossification
Thorax Hypoplastic with severe pulmonary hypoplasia
Ribs Short and flared
Multiple fractures
Short and flared
No fractures
Pelvis Arched ileum
hypoplastic ischium
Crenated ileum Hypoplastic ileum with medial spike
Femurs Proximal: Metaphyseal spikes Distal: Metaphyseal abnormalities Flared metaphyses


All three types are lethal. Diagnosis can be made as early as 12 weeks. Type II achondrogenesis gives rise to the floating head appearance: A normally ossified skull is seen against a background of poor spine mineralization.

References

  • STATdx
  • Whitley CB, Gorlin RJ. Achondrogenesis: new nosology with evidence of genetic heterogeneity. Radiology. 1983 Sep;148(3):693-8.

Tuesday, May 19, 2009

Melia

Mel is from the Latin for limb.
  • Rhizomelia (rhizo= root): Shortened proximal segment of the limb (i.e., humerus and femur)
  • Mesomelia (meso= middle): Shortened intermediate segment of the limb (i.e., radius/ulna and tibia/fibula)
  • Acromelia (acro= tip/apex): Abnormalities of the distal segment of the limb (i.e., hands and feet). Brachydactyly is shortening of the digits only.
  • Micromelia: Generalized shortening of the entire limb.
  • Amelia: Absence of a limb
  • Hemimelia: Absence of a longitudinal segment of a limb (e.g., radial aplasia or hypoplasia)
  • Phocomelia (phoco=seal; evoking the flippers of seals): Hypoplasia of the limb with hands and/or feet attached to the shoulder and hips, respectively.
  • Sirenomelia: Congenital deformity where the legs are fused, giving the appearance of a mermaid's tail.

Monday, May 18, 2009

Cloverleaf Skull

Cloverleaf skull (kleeblattschadel) occurs when there is intrauterine premature closure of all but the squamosal suture. It is classically seen with type 2 thanatophoric dysplasia, but can also be seen with severe Apert and Crouzon syndromes.

Thanatophoric dysplasia is the second most common lethal neonatal skeletal dysplasia (osteogenesis imperfecta type II is the most common). There is rhizomelia, with shortening of the humeri and femurs. Patients have very short ribs that do not extend anteriorly, and H- or U-shaped vertebral bodies.

Patients with Apert syndrome have craniosynostosis, usually of the coronary suture, and symmetric syndactyly of more than two digits involving the upper and lower extremities.

References

  • Carneiro GV et al. Apert syndrome: review and report a case. Braz J Otorhinolaryngol 2008; 74(4):640.
  • Glass RBJ et al. The Infant Skull: A Vault of Information. RadioGraphics 2004;24:507-522.
  • Glass RBJ et al. Pediatric Ribs: A Spectrum of Abnormalitie. RadioGraphics 2002; 22: 87-104.

Sunday, May 17, 2009

Turf Toe

Turf Toe refers to the hyperextension of the metatarsophalangeal joint, causing a sprain of the plantar capsule-ligament of the great toe metatarsophalangeal joint.

It is thought to be due to playing on a hard surface while wearing stiff shoes.

Reference

  • Patrick Lee, Tim B. Hunter, and Mihra Taljanovic. Musculoskeletal Colloquialisms: How Did We Come Up with These Names? RadioGraphics 2004; 24: 1009-1027.
  • Bowers KD Jr, Martin RB. Turf-toe: a shoe-surface related football injury. Med Sci Sports. 1976;8(2):81-3.

Saturday, May 16, 2009

Acroosteolysis

Acroosteolysis is the destruction of the distal phalanges.

Tufts preferentially affected
  • Scleroderma: Look for soft tissue calcifications
  • Sarcoid: Acroosteolysis can occur in 50% of patients with sarcoid of the hands. Look for small, cortical, punched-out lesions OR a permeative, lace-like pattern.
  • Psoriasis: Look for erosive disease at the distal interphalangeal joints
  • Neuropathy
    • Leprosy: Look for linear calcification of digital nerves
  • Hyperparathyroidism: Look for subperiosteal resorption
  • Thermal injury
    • Burn: Look for contractures or soft tissue calcifications.
    • Frostbite: Usually spares the thumb.
  • Epidermolysis bullosa: Hereditary disorder of marked squamous epithelial fragility and blister formation, affecting the skin and mucous membranes. Patients have numerous bullous slesions, which scar after the rupturing, leading to joint contractures, and esophageal strictures.
  • Hypertrophic osteoarthropathy: Look at soft tissues for clubbing of digits with flattening of nail bed angle and marked soft tissue swelling.
  • Pyknodysostosis: Partial agenesis of terminal phalanges (mimics acroosteolysis). Look for open cranial sutures and fontanelles, Wormian bones, scaphocephaly, sclerotic vertebrae, fractured long bones, and stubby hands.
  • Infection: Always think of osteomyelitis. This case ended up being acute osteomyelitis of the index finger (white arrow) and old osteomyelitis of the middle finger (pink arrow).
A band of lysis in middle of distal phalanx
  • Polyvinyl chloride exposure
  • Hajdu-Cheney syndrome: rare disorder of bone metabolism. The diagnosis is made by finding acroosteolysis with any three of the following: Wormian bones, open skull sutures, platybasia, micrognathia, mid-facial flattening, premature loss of teeth, coarse hair, and short stature.
  • Infection: Always think of osteomyelitis.

References

  • MSK Requisites, 3rd ed. p 331
  • Wong WL, Pemberton J. The musculoskeletal manifestations of epidermolysis bullosa: an analysis of 19 cases with a review of the literature. Br J Radiol. 1992;65(774):480-4.
  • Satishchandra H et al.Hajdu-Cheney syndrome. Indian Journal of Radiology and Imaging. 2008; 18(2):138-140.

Friday, May 15, 2009

Radiation-Induced Photopenia on Bone Scan

Patients receiving radiation therapy may develop photopenic areas on bone scan corresponding to the radiation therapy portal. Radiation-induced photopenia tends to occur at least 2 months following therapy. A dose of at least 20 Gy is apparently needed, and the effect saturates at about 50 Gy.

References

Hattner RS, Hartmeyer J, Wara WM. Characterization of radiation-induced photopenic abnormalities on bone scans. Radiology. 1982 Oct;145(1):161-3.

Thursday, May 14, 2009

Detection of Ischemia in Asymptomatic Diabetes (DIAD) Trial

The Detection of Ischemia in Asymptomatic Diabetes (DIAD) trial asked the question of whether screening adenosine-stress myocardial perfusion imaging (MPI) of asymptomatic diabetics would result in improved outcomes. The idea was that since diabetics suffer from silent (asymptomatic) ischemia, early detection of coronary artery disease (CAD) would improve outcomes.

The authors randomized about 1,200 patients between the ages of 50 and 75 who had type 2 diabetes to two groups: Those in the first group would be screened for CAD with SPECT MPI. Those in the second group would be managed clinically without SPECT MPI screening. The patients were followed up for an average of about 5 years.

The following patients were excluded:
  • Angina pectoris or chest discomfort
  • Stress test or coronary angiography within the prior 3 years
  • History of myocardial infarction, heart failure, or coronary revascularization
  • Abnormal rest ECG
  • Clinical indication for stress testing
  • Active bronchospasm (which would prevent the use of adenosine
  • Limited life expectancy due to cancer or end-stage renal or liver disease


The DIAD trial concluded that SPECT MPI of patients with asymptomatic diabetes didn’t reduce the rate of cardiac events (cardiac deaths and nonfatal infarctions). The authors admit that the study was underpowered to detect small differences between the groups, since "cardiac event rates were significantly lower than originally anticipated at the time of the design of the study" (out of the 1,200 or so patients, fewer than 20 patients in each group had cardiac events).

Finally, despite the similar outcomes in the two groups, more patients in the screened group ended up getting cardiac catheterizations.

References

Young LH, et al. Cardiac outcomes after screening for asymptomatic coronary artery disease in patients with type 2 diabetes: the DIAD study: a randomized controlled trial. JAMA. 2009 Apr 15;301(15):1547-55.

Wednesday, May 13, 2009

Differential Diagnosis of Saucerization of Bone

Saucerization is the excavation of the outer cortical margin of long tubular bones that can be seen with:
  • Soft-tissue masses
    -fibrosarcoma
    -rhabdomyosancoma
  • Ewing sarcoma
  • Lymphadenopathy
  • Aneurysm
  • Pigmented villonodular synovitis
  • Foreign body granuloma
  • Osteomyelitis

References

Mueller et al. Cortical Saucerization: An Unusual Imaging Finding of Ewing Sarcoma. AJR 163 (2): 401. (1994).

Tuesday, May 12, 2009

Transient Left Ventricular Dilatation

Transient ischemic dilation (TID) refers to an apparent increase in the size of the left ventricular cavity on stress myocardial perfusion imaging compared to rest imaging (Stolzenberg, 1980).

TID can be seen in the absence of actual left ventricular dilation. Diffuse subendocardial ischemia causes a reduction in radioisotope uptake in a subendocardial distribution, resulting in apparent enlargement of the left ventricular cavity.

Transient dilatation of the left ventricle is most commonly associated with extensive coronary artery disease (Weiss et al, 1987), but may also be seen in hypertension with myocardial hypertrophy (Robinson et al, 1997; Robinson et al, 2000; Emmett et al, 2005), dilated cardiomypathy (Robinson et al, 2000), and hypertrophic cardiomyopathy (Sugihara et al, 1990).

This patient presented with resting chest pain. He has a history of bilateral renal artery stenosis (top image) and hypertension. Myocardial perfusion imaging showed no significant perfusion defect, but there was increased size of the left ventricular cavity on stress images (Str) compared to resting images (Rst). We felt this was likely due to hypertension with myocardial hypertrophy and less likely representative of balanced ischemia in the setting of diffuse coronary artery disease. Three sets of the patient's cardiac enzymes were within normal limits.

References

  • Emmett L et al. The role of left ventricular hypertrophy and diabetes in the presence of transient ischemic dilation of the left ventricle on myocardial perfusion SPECT images. J Nucl Med 2005; 46:1596–1601.
  • Robinson VJB, et al. Transient ischemic dilatation occurs in patients without severe multivessel epicardial stenoses (abstr). J Investig Med 1997;45:226A
  • Robinson VJB, et al. Causes of Transient Dilatation of the Left Ventricle During Myocardial Perfusion Imaging. AJR 2000; 174:1349-1352.
  • Stolzenberg J. Dilation of the left ventricular cavity on stress thallium scan as an indicator of ischemic disease. Clin Nucl Med 1980;5:289 -291
  • Sugihara H et al. Assessment of transient dilation of the left ventricular cavity in patients with hypertrophic cardiomyopathy by exercise thallium-201 scintigraphy. J Nucl Med 1990; 27:1281–1289.
  • Weiss TA, Berman DS, Lew AS, et al. Transient ischemic dilation of the left ventricle on stress thallium-201 scintigraphy: a marker of severe and extensive coronary artery disease. J Am Coll Cardiol 1987;9:752 -759

Monday, May 11, 2009

Iodine perchlorate discharge test

The iodine perchlorate discharge test is used in the diagnosis of impaired organification within the thyroid. Potassium or sodium perchlorate is a competitive inhibitor of iodide trapping, resulting in release of untrapped iodide from the thyroid. When organification is normal, perchlorate does not cause a significant change in the iodide content of the thyroid, since most iodide is organified and cannot be released. When organification is impaired, perchlorate causes a decrease in thyroid iodide content.

The test is performed by quantifying thyroid uptake two hours after administration of radiolabeled iodine. One hour after administration of potassium perchlorate, thyroid uptake is again quantified. In normal subjects, the uptake values remain relatively unchanged. In patients with impaired organification, there is a decrease of greater than 5% following perchlorate administration.

References

Sarkar SD and Becker DV. Thyroid uptake and imaging (Chapter 34). in Principles and Practice of Endocrinology and Metabolism, Third Edition. Becker KL et al (eds). Lippincott Williams & Wilkins (2002).

Sunday, May 10, 2009

Ectrodactyly


Terminal transverse defects are a broad category limb dysplasias where there is absence or hypoplasia of the distal limbs with relatively intact proximal structures. More severe forms of terminal transverse defects include hemimelia or amelia.

Ectrodactyly (from the Greek ektroma, abortion and daktylos, finger) is a subcategory of terminal transverse defects that refers to the absence of more distal elements and can include aphalangia (absence of phalange(s)), adactylia (absence of finger(s)), or the entire hand (acheiria). The feet are uncommonly affected.

Split-hand/-foot malformations are a class of ectrodactyly that can present as absence of a central ray resulting in a cleft (as seen in the first case above), or absence of the radial rays with monodactyly of the fifth digit.

The 'lobster claw' deformity is a type of split-hand/-foot malformation, where there is absence of the middle digit with formation of a cleft hand, and syndactyly of the digits on either side of the cleft. This deformity is associated with ectrodactyly-ectodermal dysplasia-cleft palate (EEC, Walker-Clodius) syndrome and autosomal dominant ectrodactyly syndrome.

Ectrodactyly is a rare condition, with sporadic ectrodactyly being more common than syndromic presentations. A notable exception is the Vadoma tribe of Zimbabwe, in whom the condition is more common.

Special thanks to Dr. Rolando Reyna for the second case of ectrodactyly shown above.

References

Saturday, May 9, 2009

Fluid-Fluid Levels in Bone Lesions

The differential diagnosis for fluid-fluid levels in bone lesions include:

Reference

MSK Requisites. 3rd edition. p 418

Friday, May 8, 2009

Octreotide Imaging

Background

In-111 pentetreotide imaging (octreoscan) is used for the detection and localization of neuroendocrine tumors.

Somatostatin attaches to receptors Neuroendocrine tumors and acts as an inhibitor. Somatostatin has a very short plasma half life (a few minutes), so somatostatin analogs are used for imaging and treatment. Octreotide (Sandostatin) is the the somatostatin analog used in nuclear medicine and has a half life of about 2 hours. Chelation of octreotide to In-111 is achieved using DTPA, resulting in In-111 pentetreotide.

While somatostatin binds to all subtypes of somatostatin receptors, octreotide only attaches to subtypes 2 and 5. 80% of neuroendocrine tumors have type 2 somatostatin receptors, which means that a negative In-111 pentetreotide scan doesn't mean a neuroendocrine tumor is not present.

Indications

Somatostatin receptors can be found on neuroendocrine and some non-neuroendocrine tumors. These include:
Tumor Sensitivity comments
carcinoid 80-90%  
paraganglioma 94%  
gastrinoma 75-93%  
VIPoma 88%  
insulinoma 40-50%  
glucagonoma unknown  
medullary thyroid cancer 41% PET is much more sensitive, but octeroscan should be first line
benign pheochromocytoma 58%  
malignant pheochromocytoma 87%  
neuroblastoma   I-123 MIBG is preferred
small-cell lung cancer 92% Sensitivity for mediastinal lymph nodes is about 80%, but low for extrathoracic metastatic lesions
pituitary adenoma    
meningiomas    
well-differentiated gliomas    
lymphoma    
breast carcinoma    


Thyroid uptake can also be seen in patients with endemic goiter with or without thyroid autonomy.

Patient Preparation

Patients with neuroendocrine tumors may receive somatostatin analogs (e.g., octreotide) for treatment. This bound somatostatin may compete with In-111 pentetreotide and result in a false negative study. Therefore, it is recommended that patients stop any somatostatin analog treatment 72 hours before imaging.

Another issue is bowel activity. Overnight bowel prep with a laxative is sometimes recommended. Patients with carcinoid syndrome who have diarrhea may skip the bowel preparation.

Normal biodistribution

The normal biodistribution of In-111 pentetreotide is shown. The thyroid, liver, spleen, kidneys, and bladder are always seen with variable uptake in the gastrointestinal tract on delayed images.

False Positive

Somatostatin receptors may be expressed in chronic granulomatous processes such as sarcoidosis, tuberculosis and in chronic inflammatory diseases like Crohn disease, ulcerative colitis, and rheumatoid arthritis, leading to false positive results.

References

  • Becker W, Schrell U, Buchfelder M, Hensen J, Wendler J, Gramatzki M, Wolf F. Somatostatin receptor expression in the thyroid demonstrated with 111In-octreotide scintigraphy. Nuklearmedizin. 1995 Jun;34(3):100-3.
  • Intenzo CM, Jabbour S, Lin HC, Miller JL, Kim SM, Capuzzi DM, Mitchell EP. Scintigraphic imaging of body neuroendocrine tumors. Radiographics. 2007 Sep-Oct;27(5):1355-69.
  • Tzannou IA et al. The use of radiolabeled somatostatin analog scintigraphy in the staging of small cell lung cancer patients. Am J Clin Oncol. 2007 Oct;30(5):503-6.

Thursday, May 7, 2009

Stunned and Hibernating Myocardium on Tc-99m Sestamibi

Myocardial stunning is transient systolic ventricular dysfunction that occurs in the acute post-ischemic period and may persist for several weeks even in the face of normal perfusion.

Myocardial hibernation refers to dysfunctional resting left ventricular contractility associated with a mild to moderate fixed defect. This ventricular dysfunction improves following revascularization.

It is thought that repeated episodes of ischemia result in hibernation by causing repetitive myocardial stunning. Hibernation is seen as a defense mechanism by underperfused myocytes.

18F-FDG-PET imaging is the gold standard for assessment of myocardial viability. Hibernating myocardium will appear as an area of fixed perfusion defect on sestamibi perfusion images. 18F-FDG-PET, on the other hand, will show metabolic activity in areas of hibernating (and viable) myocardium (perfusion/metabolism mismatch). A glucose load 1-2 hours prior to imaging will increase insulin levels and increase myocardial glucose uptake.

Stunned myocardium, on the other hand, will show preserved basal perfusion in a dysfunctional segment of myocardium. 18F-FDG-PET will show preserved metabolism in this area.

Wednesday, May 6, 2009

Focal nodular hyperplasia

Background

Focal nodular hyperplasia (FNH) is a benign hepatic tumor. It is the second most common liver tumor (after hemangioma). It is caused by a hyperplastic response to a localized vascular abnormality.

Imaging Findings

FNH may appear as a iso- or hypoattenuating lesion on noncontrast CT. It shows intense enhancement during arterial phase of contrast enhancement, but becomes iso- or hypoattenuating during the portal venous phase (Figure 1A). On delayed images, it becomes isoattenuating compared to liver with a hyperattenuating central scar.

T1-weighted images show an iso- to slightly hypointense mass with a hypointense central scar (Figure 1B). T2-weighted images show an iso- to slightly hyperintense mass with a hyperintense central scar and a hyperintense pseudocapsule (Figure 1C). Dynamic contrast-enhanced T1-weighted images show a homogeneous hyperintense mass and hypointense central scar during the arterial phase (Figure 1D) and an isointense mass during the portal venous phase (Figure 1E). Delayed images show an isointense mass with a hyperintense central scar, as well as enhancement of the pseudocapsule (Figure 1F).

The pseudocapsule is due to compression of liver parenchyma surrounding the FNH, vessels surrounding FNH, as well as inflammation.

On F18-FDG PET, FNH typically has uptake similar to or lower than adjacent liver.

Differential diagnosis

  • Hepatic adenoma
  • Fibrolamellar heptaocellular carcinoma: Has a fibrous scar that is hypointense on T2-weighted images. Enhancement typically heterogeneous.
  • Hepatocellular carcinoma (HCC): A tumor capsule (as opposed to a pseudocapsule) may be seen in HCC and is hypointense on T1- and T2-weighted images and it demonstrates enhancement on delayed images.
  • Small cavernous hemangioma

Tuesday, May 5, 2009

Colloid Shift

In 99mTc Sulfur colloid scan, a colloid shift refers to the abnormal biodistribution of radiotracer.

Figure 1: Normal sulfur colloid biodistribution shows radiotracer predominantly within the liver.In a normal sulfur colloid scan, 80-90% of the injected colloid particles end up in the liver. The majority of the remainder localizes to the spleen. What little is left, ends up in the bone marrow, but usually in insufficient amounts to show up on imaging.

Figure 2: Colloid shift is seen in this sulfur colloid scan with increased radiotracer uptake in the spleen and bone marrow. Also seen here is hepatosplenomegaly.When this normal biodistribution is disrupted, we get increased uptake of radiotracer in the spleen and bone marrow compared to the liver.

The most common causes of colloid shift are hepatic cirrhosis, diffuse hepatic metastases, diabetes, and blunt trauma to the spleen (Briggs and Amberson, 1987).

references

Briggs RC and Amberson SM. Colloid Shift Following Blunt Trauma. J NuclMed 28:188-190, 1987 Mettler FA and Guiberteau MJ. Chapter 8: Gastrointestinal Tract. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006

Monday, May 4, 2009

Amiodarone-induced thyrotoxicosis and hypothyroidism

Amiodarone is an antiarrhythmic medication that contains more than 35% iodine by weight. Amiodarone can cause iodine overload up to 100 times the normal daily intake.

Amiodarone-induced thyrotoxicosis

Amiodarone-induced thyrotoxicosis (AIT) can occur during amiodarone therapy or even long after amiodarone withdrawal. AIT is associated with increased mortality, especially in elderly patients with left ventricular dysfunction.

Two types of AIT have been described. Type I occurs in patients with underlying thyroid disease, and reflects increased function triggered by the iodine load of amiodarone. The mechanism is referred to as the Jod-Basedow effect: hyperthyroidism following administration of iodine or iodide. It is treated using potassium perchlorate (decreases uptake of iodine into the thyroid) and methimazole (inhibits addition of iodine to thyroglobulin).

Type II AIT, on the other hand, occurs in patients with no underlying thyroid disease and is thought to be caused by destruction of the thyroid gland by iodine or amiodarone or one of its metabolites. The destruction of the thyroid gland leads to leakage of preformed hormones from damaged follicles. Type II AIT is treated with steroids.

The scintigraphic findings are similar to those seen with destructive (subacute) thyroiditis: Low activity in the gland with low (less than 2% at 24 hours) uptake.

Amiodarone-induced hypothyroidism

Amiodarone-induced hypothyroidism (AIH) is thought to occur via the Wolff-Chaikoff effect (inhibition of thyroid hormone production due to iodine overload). AIH is treated with L-T4.

references

Martino E, Bartalena L, Bogazzi F & Braverman LE. The effects of amiodarone on the thyroid. Endocrine Reviews 2001; 22:240–254.
O'Sullivan AJ, Lewis M & Diamond T. Amiodarone-induced thyrotoxicosis: left ventricular dysfunction is associated with increased mortality. European Journal of Endocrinology 2006; 154:533–536.

Sunday, May 3, 2009

Grading Lung Uptake on Gallium Scan

Diffuse uptake of Gallium by the lungs may be normal at 24 hours, but abnormal at 48 hours. Gallium uptake at 48 hours can be graded to aid in diagnosis. A grade of 2 or more is considered abnormal. The posterior projection is used, as it is thought to minimize sensitivity to differences in body size, gender, and habitus.
Grade Amount of Uptake
1 Similar to soft tissue background
2 Greater than soft tissue, but less than bone marrow
3 Greater than bone marrow, but less than liver
4 Greater than liver
I'm unable to find a peer-reviewed reference addressing the specificity and sensitivity of different grades for different pathologic processes.

Diffusely increased lung uptake on 67Ga can be seen with:
  • Infection: Pneumocystis jiroveci, Mycobacterium, etc.
  • Hypersensitivity pneumonitis:
  • Sarcoidosis:

References

Line BR at al. Gallium-67 scanning to stage the alveolitis of sarcoidosis: correlation with clinical studies, pulmonary function studies, and bronchoalveolar lavage. Am Rev Respir Dis. 1981 Apr;123(4 Pt 1):440-6. Line BR, Hunninghake GW, Keogh BA, Jones AE, Johnston GS, Crystal RG

Saturday, May 2, 2009

Crossed Cerebellar Diaschisis

Crossed cerebellar diaschisis is decreased metabolism in a cerebellar hemisphere contralateral to a cerebral hemispheric lesion. Lesions located in the motor cortex, anterior corona radiata, and thalamus lead to the most prominent suppression of metabolism in the contralateral cerebellar hemisphere.

References

Roarke M, Dedashti F. Crossed cerebellar diaschisis. 11/2/1995.

Friday, May 1, 2009

Congenital Anterolateral Tibial Bowing and Polydactyly

Congenital anterolateral tibial bowing and polydactyly (CATBP) is, as its name explicitly states, a syndrome of congenital anterolateral tibial bowing and polydactyly. This rare condition is important because anterolateral tibial bowing usually raises concern for neurofibromatosis type 1; in contrast to NF1, however, there are no neurocutaneous signs in CATBP and the prognosis tends to be better.

CATBP is associated with hallux, first metatarsus, tarsus, and sometimes tibial duplication. The fibula is often without apparent involvement, but may develop proximal overgrowth later. Hand malformations, including syndactyly, pre-axial polydactyly, clinodactyly, and radial deviation of the index finger have also been reported.

Delta Tibia

Based on my admittedly cursory review of the literature, the tibial abnormality in CATBP seems to be what Currarino refers to as "the delta tibia," since both Currarino and Lemire refer to the same literature in citing previous examples of their cases. What follows is based on Currarino's description of the delta tibia.

Frontal radiographs reveal the lateral component of the anterolateral bowing, but the appearance of the curve is nonspecific. The lateral view has more specific features. Lateral radiographs reveal an anterior curve of the tibia with the apex at or slightly below the center of the tibial diaphysis or at the junction between the middle and distal third of the tibia. The tibia also appears divided into two pointed segments with their points at the apex of the curve (pink arrows) with an intervening anterior cortical defect (blue arrow).

Instead of the inward smooth cortical thickening seen in the concavity of the curve in most types of tibial bowing, there is a triangular osseous structure (green arrow) connected to the posterior surface of the two tibial segments.

The fibula is intact, straight, and longer than the tibia, with its proximal end displaced laterally.

References

  • Lemire EG. Congenital anterolateral tibial bowing and polydactyly: a case report. J Med Case Reports. 2007 Jul 23;1:54.
  • Currarino G, Herring JA, Johnston CE Jr, Birch JG. An unusual form of congenital anterolateral tibial angulation-the delta tibia. Pediatr Radiol. 2003 May;33(5):346-53.