Types of Primary Osteoporosis

Primary osteoporosis can be divided into type I (postmenopausal) osteoporosis and type II (senile) osteoporosis.

Type I osteoporosis results from loss of estrogen and predominantly affects trabecular/cancellous bone. Type I osteoporosis is most frequently associated with vertebral and wrist fractures in postmenopausal women.

Type II osteoporosis, on the other hand, results from diminished absorption of calcium and reduced serum levels of vitamin D, leading predominantly to resorption of cortical bone. Type II osteoporosis is associated with hip fractures in men and women older than 70 or so.

References

Duque G, Troen BR. Understanding the mechanisms of senile osteoporosis: new facts for a major geriatric syndrome. J Am Geriatr Soc. 2008 May;56(5):935-41.

Solitary Skull Lesions

A mnemonic for solitary skull lesions is "I help me"

• Infection: Permeative margin
• Hemangioma: Well-circumscribed diploic space lesion with a "Spoke wheel" or "reticulated" pattern
• Epidermoid/dermoid: Epidermoid has sclerotic margins
• Leptomeningeal cyst: Smoothly marginated skull defect. "Growing fracture" refers to dural herniation and expansion of defect.
• Plasmacytoma: Scalloped, poorly marginated, non-sclerotic skull base margin.
• Paget: AKA osteoporosis circumscripta. Lytic phase shows a well-defined defect with involvement of the inner > outer tables. More common in the frontal bone. Look for cortical thickening and coarse trabeculation.
• Post surgical: Well-marginated
• Metastases: Permeative margin
• Eosinophilic granuloma: Beveled edge (inner table involved to a greater extent than the outer table). Properly called Langerhans cell histiocytosis under the new classification of histiocytic disordere.
• Encephalocele: Conegnital form is usually parietal or occipital.

In addition to being needlessly long, this mnemonic has the added benefit of being impossible to remember.

Oncogenic (Tumoral) Osteomalacia

Oncogenic osteomalacia occurs with bone or soft-tissue tumors and is characterized by renal phosphate wasting and hypophosphatemia and decreased serum 1,25-dihydroxycholecalciferol levels. Patients with rickets or osteomalacia unexplained by nutrition should be investigated for occult tumor.

Oncogenic osteomalacia is most frequently associated with the phosphaturic mesenchymal tumor, mixed connective tissue variant, but a search for more common tumors such as prostate, breast, small-cell carcinoma of the lung, fibrous dysplasia, and neurofibromatosis is also indicated.

Many cases of hemangiopericytoma leading to oncogenic osteomalacia are now thought to actually represent cases of phosphaturic mesenchymal tumor. In addition, the concept of hemangiopericytoma as a distinct entity has been called into question.

References

• Avila NA, Skarulis M, Rubino DM, Doppman JL. Oncogenic osteomalacia: lesion detection by MR skeletal survey. AJR Am J Roentgenol. 1996 Aug;167(2):343-5.
• Folpe AL, Fanburg-Smith JC, Billings SD, Bisceglia M, Bertoni F, Cho JY, Econs MJ, Inwards CY, Jan de Beur SM, Mentzel T, Montgomery E, Michal M, Miettinen M, Mills SE, Reith JD, O'Connell JX, Rosenberg AE, Rubin BP, Sweet DE, Vinh TN, Wold LE, Wehrli BM, White KE, Zaino RJ, Weiss SW. Most osteomalacia-associated mesenchymal tumors are a single histopathologic entity: an analysis of 32 cases and a comprehensive review of the literature. Am J Surg Pathol. 2004 Jan;28(1):1-30.
• Renton P, Shaw DG. Hypophosphatemic-osteomalacia secondary to vascular tumors of bone and soft tissue. Skeletal Radiol 1976; 5:21-24.

Salter I Fractures of the Toes: Not So Simple

Salter I fractures of the great toe, as seen with stubbed toe injuries, should be considered occult compound fractures due to the intimate relationship of skin, nail, and bone in the toes. As a result, fractures through the growth plate of a distal phalanx carry a high risk of infection and should be treated accordingly.

References

Pinckney LE; Currarino G; Kennedy LA. The stubbed great toe: a cause of occult compound fracture and infection. Radiology. 1981; 138(2):375-7

Pelvic Avulsion Fractures

Avulsion fractures can occur at many points in the pelvis. Going clockwise from the iliac crest to the pubic symphysis on the left we have:

• Iliac crest: Abdominal muscles
• Anterior superior iliac crest: Sartorius
• Anterior inferior iliac crest: Rectus femoris
• Greater trochanter: Gluteal muscles
• Lesser trochanter: Iliopsoas. Isolated nontraumatic avulsion fractures of the lesser trochanter in adults is a pathognomonic sign of metastatic disease.
• Ischial tuberosity: Hamstrings
• Pubic symphysis: Adductor group

A stupid mnemonic is: Alabama's stoned rappers got ill hunting armadillos.

References

Bui-Mansfield LT, Chew FS, Lenchik L, Kline MJ, Boles CA. Nontraumatic avulsions of the pelvis. AJR Am J Roentgenol. 2002 Feb;178(2):423-7.

Tennis Leg

Tennis leg classically presents in a middle-aged person with sport-related acute pain in the middle portion of the calf, associated with a snapping sensation. Initially attributed to rupture of the plantaris tendon, more recent work has implicated rupture of the medial head of the gastrocnemius muscle at the musculotendinous junction as a more common etiology.

References

Delgado GJ, Chung CB, Lektrakul N, Azocar P, Botte MJ, Coria D, Bosch E, Resnick D. Tennis leg: clinical US study of 141 patients and anatomic investigation of four cadavers with MR imaging and US. Radiology. 2002 Jul;224(1):112-9.

Unilateral Rib Notching

Rib notching can be caused by collateral flow through intercostal vessels from the following conditions:

• Coarctation of the aorta proximal to the left subclavian artery: Right-sided
• Coarctation of the aorta with an aberrant right subclavian artery: Left-sided. Occurs when the aberrant right subclavian artery arises after the coarctation.
• Subclavian artery stenosis: Ipsilateral to the side of stenosis
• Blalock-Thomas-Taussig shunt: Ipsilateral to the side of shunt. Due to division of all the branches of the first part of the subclavian artery performed during shunt creation.
• Neurofibromatosis of the intercostal nerves:
• Vascular malformations of the thoracic wall: Enlarged intercostal veins cause the rib notching.
• Superior vena cava obstruction: Due to development of collateral channels to the inferior vena cava via the intercostal veins
• Taboparesis:

References

• Shapiro S, Schrire V. Unilateral notching of the ribs in cyanotic heart disease. Br Heart J. 1964 Sep; 26:620-4.

Greedy Fat Radiologists Want Big Pizzas

Many shunt procedures for congenital heart disease connect a vessel to a pulmonary artery. A mnemonic for these shunts (in order of blood flow from the superior vena cava down into the descending aorta) is "Greedy Fat Radiologists Want Big Pizzas":

Glenn	SVC	to	PA
Fontan	RA	to	PA
Rastelli	RV	to	PA
Waterston-Cooley	Ascending aorta	to	PA
Blalock-Thomas-Taussig	Subclavian artery	to	PA
Potts	Descending aorta	to	PA

The Waterston and Potts shunts are out of favor due to the high incidence of pulmonary hypertension and CHF.

The Rastelli procedure is used in patients with D-transposition of the great vessels and ventricular septal defects with some degree of left ventricular outflow obstruction (small or abnormal pulmonary valve). Performing the Jatene (arterial switch) procedure in such cases may result in pulmonary stenosis. Rastelli procedure is indicated in such cases. It involves 1) Dividing the pulmonary artery just above the pulmonic valve, 2) Creating an intraventricular tunnel that redirects blood from the left ventricle through the ventricular septal defect into the ascending aorta, and 3) Creating an external conduit from the right ventricle to the pulmonary artery.

At the end of the Rastelli procedure left ventricular blood goes to the aorta and right ventricular blood goes to the pulmonary arteries, correcting the transposition at the ventricular level.

The Rastelli procedure can also be used in cases of pulmonary outflow tract obstruction with an overriding aorta.

References

Gaca AM, Jaggers JJ, Dudley LT, Bisset GS 3rd. Repair of congenital heart disease: a primer-part 1. Radiology. 2008 Jun;247(3):617-31.

Constrictive Pericarditis vs Restrictive Cardiomyopathy

Constrictive pericarditis is caused by adhesions between the visceral and parietal layers of the pericardium. It most commonly occurs following cardiac surgery, radiation therapy, or pericarditis of any etiology. Uremic and viral pericarditis are more common in the west, while tuberculous pericarditis remains popular in the developing world.

Eggshell Calcification of the pericardium is suggestive of Constrictive pericarditis, but its absence does not rule out constrictive pericarditis. Thick, shaggy, and amorphous calcifications are typical of tuberculous pericarditis.

Demonstration of pericardial adhesions can be done on MRI cine gradient echo images with tag lines applied perpendicular to the pericardium. In normal pericardium, these lines, which are placed during systole, break on cine images. In constrictive pericarditis, on the other hand, adhesions keep the pericardium from moving, resulting in intact, but stretched, tag lines.

Cine MR may also show the characteristic septal bounce: As the tricuspid valve opens, the interventricular septum bounces to the left.

Thickening of the pericardium (> 4 mm) is also suggestive.

The physiologic consequence of these adhesions is incomplete diastolic filling of the heart that results in dilatation of the right atrium, superior and inferior venae cavae, and hepatic and azygos veins. Hepatic venous congestion, in turn, may result in the nutmeg liver appearance. The right ventricle may be normal in size or narrowed.

A mnemonic that works for me is "CA Ca"=Constrictive Adhesions Calcification.

Restrictive cardiomyopathy and constrictive pericarditis may cause identical hemodynamic findings. Restrictive cardiomyopathy is rare and is caused by an infiltrative process that leads to myocardial stiffening (as opposed to the pericardial adhesions of constrictive pericarditis). It is most often seen in dialysis patients with chronic amyloidosis. The pericardial findings in constrictive pericarditis (see above) would obviously not be seen in restrictive cardiomyopathy.

References

Miller SW and Boxt LM. Chapter 8. in Cardiac Imaging, the Requisites Third edition, Miller SW, Boxt LM, and Abbara S, eds. Mosby 2009. pp 269-271.

Thyroid Radioiodide Uptake (RAIU) Curves

Thyroid uptake may be quantified at 4-6 hours and at 24 hours. The gray bars define the rough normal ranges at 4-6 hours (5%-20%) and 24 hours (10%-35%).

Hyperthyroid patients will have elevated 4-hour uptake values. In cases of rapidly turning over iodine pool (e.g., Graves disease), there will be an early peak followed by a gradual decline. In such cases, 24-hour uptakes may be in the normal range.

Patients with subacute thyroiditis (not shown) will be hyperthyroid clinically, but will demonstrate low or imperceptible uptake.

Patients with renal disease will have a prolonged uptake due to decreased urinary excretion of the iodine.

References

• Becker D, Charkes ND, Dworkin H, Hurley J, McDougall IR, Price D, Royal H, Sarkar S. Procedure guideline for thyroid uptake measurement: 1.0. Society of Nuclear Medicine. J Nucl Med. 1996 Jul;37(7):1266-8.
• Franklyn J and Shephard M. Evaluation of Thyroid Function in Health and Disease Revised 21 September 2000.

Technetium Misbehaving

Unbalanced equations of technetium reduction and tagging are shown. The first equation shows the normal case, where pertechnetate (7+) is reduced (3+, 4+, 5+) by stannous chloride to enable tagging a pharmaceutical.

The second equation shows the case of air contamination. This generates free pertechnetate, which accumulates in the stomach and thyroid and salivary glands. Paper chromatography with acetone will show free pertechnetate advancing with the solvent front.

The third equation shows the case of water contamination, generating technetium dioxide ("hydrolyzed technetium") and stannous hydroxide, a colloid. Technetium dioxide will accumulate in the liver. The stannous ions may cause red blood cell labeling. Residual stannous ions in the blood may also result in inadvertant in vivo red blood cell labeling if another pertechentate scan (e.g., thyroid or Meckel) is attempted within a week.

Paper chromatography with saline as the solvent will show technetium dioxide at the origin and water soluble tracers (e.g., DTPA) advancing with the solvent front.

References

• Johnson AE, Gollan F. 99mTc-technetium dioxide for liver scanning. J Nucl Med. 1970 Sep;11(9):564-5.
• Mettler FA and Guiberteau MJ. Chapter 3. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 44-45.

Nuclear Medicine in the Evaluation of the Renal Transplant

There is also a related post on the use of ultrasound in evaluation of renal transplants.

Immediate (first week) complications:

• Acute tubular necrosis (ATN): More common in cadaveric transplants. There is preserved or only mildly reduced perfusion with increased T_max and T_1/2. Dynamic imaging reveals marked parenchymal retention. Nice images can be found at RiT Radiology.
• Accelerated acute rejection: Presents within a few days to a few weeks following transplantation.
• Renal vein thrombosis: Decreased or absent perfusion with increased T_max and T_1/2. In complete thrombosis, there is a reniform photopenic area outlined by background activity.
• Renal artery thrombosis: Decreased or absent perfusion with increased T_max and T_1/2. In complete thrombosis, there is a reniform photopenic area outlined by background activity.

Early (1-4 weeks) complications:

• Acute rejection: There is decreased perfusion and increased T_max and T_1/2. These findings may be similar to those of acute tubular necrosis. The time course of disease appearance can help differentiate the two. In addition, acute rejection will show decrease in function on serial radionuclide imaging studies, highlighting the importance of obtaining a baseline study.
• Urine leak or fistula: May see excreted radiotracer adjacent to transplanted kidney.
• Ureteral obstruction: Findings are similar to those of ureteral obstruction in native kidneys.

Late (> 4 weeks) complications:

• Drug toxicity: Acute cyclosporine toxicity resembles mild acute rejection or acute tubular necrosis, with normal or decreased perfusion and with parenchymal retention.
• Renal artery stenosis: Most common vascular complication of transplantation. Findings are similar to those of chronic rejection, with decreased perfusion, normal parenchymal transit, and absent or minimal cortical retention. Post-captopril images will show findings seen in renovascular hypertension: decreased activity with DTPA and increased parenchymal retention with MAG-3.
• Recurrence of native renal disease:
• Lymphocele: Most are asymptomatic and do not require therapy, but some can exert mass effect and impair renal function. A large photopenic region may be seen exerting mass effect on the transplanted kidney.
• Chronic rejection: Thin cortex and mild hydronephrosis with diminished uptake of tracer and normal parenchymal transit. Early chronic rejection may have absent or minimal cortical retention, but there may be parenchymal retention of radiotracer with advanced chronic rejection.

References

• Brown ED, Chen MY, Wolfman NT, Ott DJ, Watson NE Jr. Complications of renal transplantation: evaluation with US and radionuclide imaging. Radiographics. 2000 May-Jun;20(3):607-22.
• Mettler FA and Guiberteau MJ. Chapter 10. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 314-318.

Indications and Contraindications to Stress Cardiac Perfusion Imaging

Distilled from the American Society of Nuclear Cardiology guidelines:

The indications for the various stress methods are the same, with adenosine/dipyridamole allowing for evaluation of very early MI and better evaluation of patients with baseline ECG abnormalities (LBBB, Wolff-Parkinson-White syndrome, and permanent ventricular pacing). Dobutamine is reserved for patients who can't have treadmill or adenosine/dipyridamole studies.

The absolute contraindications for adenosine and dipyridamole include active asthma (controlled asthma should be OK) and second- and third- degree AV block (only a relative contraindication in exercise stress). Unstable angina is an absolute contraindication to treadmill and dobutamine stress.

MIBG vs. Octreotide in the Diagnosis of Neuroendocrine Tumors

MIBG and octreotide can both localize to neuroendocrine tumors (pheochromocytoma, paraganglioma, neuroblastoma, and carcinoid). In almost all cases, MIBG is the way to go. The exceptions are carcinoids and extraadrenal pheochromocytomas.

Neither seem to be that great for medullary thyroid cancer, but octreotide seems to offer better sensitivity for cervical and upper mediastinal lymph nodes in patients with occult disease.

Pheochromocytoma and Paragangliomas

MIBG is used to localize clinically suspected pheochromocytoma, to confirm that a mass is a pheochromocytoma, or to exclude metastatic disease. For adrenal pheochromocytomas, MIBG has close to 100% specificity but lower sensitivity (86%). Octreotide can also localize adrenal pheochromocytomas, but has a lower sensitivity than MIBG (20%-50%). It can be used in cases of negative MIBG scans.

In extraadrenal pheochromocytomas, on the other hand, MIBG has a lower sensitivity (72%) than octreotide (96%), especially those of the head and neck.

Neuroblastoma

MIBG is the most effective indicator of neuroblastoma and is used in staging at presentation, restaging after treatment, searching for postsurgical residual tumor, monitoring the effect of treatment, and diagnosis of recurrence.

Octreotide has lower sensitivity (64%) compared to MIBG (94%) and does not have a well-defined indication in children with neuroblastoma. Since the presence of somatostatin receptors is associated longer survival, octreotide imaging may provide some prognostic information.

Carcinoid

Octreotide has higher sensitivity (>80%) than MIBG in detecting primary and metastatic lesions. Octreotide also has higher sensitivity for localizing primary tumor and extra-hepatic involvement. MIBG and octreotide are of similar sensitivity and specificity in detecting liver metastases. In addition, some carcinoids not seen on octreotide imaging may have MIBG uptake.

Medullary Thyroid Carcinoma

Nuclear medicine plays a minor role in the preoperative evaluation of medullary thyroid carcinoma, but is an essential part in postoperative follow-up. Medullary thyroid carcinoma recurs in about 50% of patients and may present a diagnostic challenge, especially in the case of liver metastases which tend to be miliary.

MIBG provides high specificity but low (30%) sensitivity and is used primarily in locating adrenal medullary hyperplasia or pheochromocytoma in MEN syndromes. MIBG is also used to evaluated MIBG uptake in known lesions prior to ¹³¹I-MIBG therapy.

Octreotide seems to offer high sensitivity for cervical and upper mediastinal lymph nodes in patients with occult disease, but is less sensitive in patients with distant metastases and progressive disease.

References

• Chen L, Li F, Zhuang H, Jing H, Du Y, Zeng Z. ^99mTc-HYNIC-TOC scintigraphy is superior to 131I-MIBG imaging in the evaluation of extraadrenal pheochromocytoma. J Nucl Med. 2009 Mar;50(3):397-400. Epub 2009 Feb 17.
• Koopmans KP, Jager PL, Kema IP, Kerstens MN, Albers F, Dullaart RP. ¹¹¹In-octreotide is superior to ¹²³I-metaiodobenzylguanidine for scintigraphic detection of head and neck paragangliomas. J Nucl Med. 2008 Aug;49(8):1232-7. Epub 2008 Jul 16.
• Rufini V, Calcagni ML, Baum RP. Imaging of neuroendocrine tumors. Semin Nucl Med. 2006 Jul;36(3):228-47.
• Tenenbaum F, Lumbroso J, Schlumberger M, Mure A, Plouin PF, Caillou B, Parmentier C. Comparison of radiolabeled octreotide and meta-iodobenzylguanidine (MIBG) scintigraphy in malignant pheochromocytoma. J Nucl Med. 1995 Jan;36(1):1-6.

Prognostic Information Available from Cardiac Perfusion and Functional Studies

• Number of reversible defects is an indicator of multivessel disease and predictor of future adverse cardiac events. Single reversible defect does not exclude multivessel disease, but more than one reversible defect predicts multivessel disease.
• Size and severity of reversible defects is an indicator of myocardium at risk and predictor of future adverse cardiac events.
• Extent of fixed defects is predictor of future adverse cardiac events.
• Abnormal lung accumulation of ²⁰¹Tl: > 50% lung-to-heart ratio on exercise and > 65% on dypiridamole stress is a marker for transient left ventricular dysfunction at exercise and correlates with multivessel disease and increased morbidity and mortality rates.
• Transient ischemic dilatation in the setting of coronary artery diseae indicates multivessel or left main disease and is predictor of future adverse cardiac events.
• Normal perfusion is associated with a less than 1% risk of adverse myocardial event per year.
• Nonfatal myocardial infarctions better predicted by reversible perfusion abnormalities than LVEF.
• LVEF < 45% or ESV > 70 cc associated with high mortality.
• LVEF > 45% or ESV < 70 cc associated with low mortality (< 1%/year) even in the presence of severe perfusion abnormalities.

Sulfur Colloid vs Tagged Red Blood Cells for Gastrointestinal Hemorrhage

Red blood cells and sulfur colloid are tagged with ^99mTc-tagged red blood cells remain intravascular and are better at detecting intermittent bleeding. Preparation of tagged red blood cells, however, is a bit involved.

Sulfur colloid is easy to prepare and readily available. It is taken up by the reticuloendothelial system, providing great target to background contrast as long as the bleeding site is not over the liver or spleen. The speed of clearance (vascular half-life=3.5 minutes) is also a disadvantage when it comes to intermittent bleeding.

References

Mettler FA and Guiberteau MJ. Chapter 8. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 215-216.

Positive Triple-Phase Bone Scan: Differential Diagnosis

Differential Diagnosis for Positive Triple-Phase Bone Scan The following conditions will result in increased activity in all three phases of a triple-phase bone scan (blood flow, blood pool, delayed) :

• Osteomyelitis
• Fracture
• Tumor
• Osteoid osteoma
• Charcot joint
• Reflex sympathetic dystrophy: Uptake involves entire extremity. 50% of patients have increased blood flow and blood pool uptake, while 95% have increased uptake on delayed images.
• Osteonecrosis
• Osteoarthritis

Renal Cortical Agents

While MAG-3 and to a lesser extent DTPA provide some visualization of the renal parenchyma, we need radiotracers that bind to the renal tubules for adequate cortical visualization. Two such agents are available: DMSA and glucoheptonate, both of which are bound to ^99mTc.

DMSA binds to the cortex better and provides greater activity, allowing better resolution of cortical defects, making it the preferred agent in small infants. The renal cortical exposure is about the same for DMSA and glucoheptonate, but DMSA provides lower gonadal and bladder exposure.

Renal cortical imaging is very sensitive for the diagnosis of renal parenchymal infection and is the imaging procedure of choice when there is an uncertain diagnosis of acute pyelonephritis in children. Acute pyelonephritis may present as a focal defect, multiple defects, or diffusely decreased uptake. Defects are also seen in areas of cortical scarring.

	DMSA	Glucoheptonate
Kinetics	40% concentrated in tubules by 6 hours and remainder excreted slowly.	Filtration and tubular excretion.
Renal function estimate	None	Early images can be used to assess renal perfusion
Ureters and bladder	-	+
Imaging	Immediate and 2-4 hours. Longer if impaired renal function.	Immediate.
Disadvantages	Short shelf-life.
Dose-limiting organ	Kidneys.	Bladder.
Dose	37-185 MBq (1-5 mCi)	370-740 MBq (10-20 mCi)

References

• Mettler FA and Guiberteau MJ. Chapter 10. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 294-295.
• Mandell GA, et al. Society of Nuclear Medicine Procedure Guideline for Renal Cortical Scintigraphy in Children.

Panda Sign in Nuclear Medicine

The panda sign in nuclear medicine refers to uptake on a Gallium scan in the lacrimal, parotid, and salivary glands. Differential considerations are:

• Sarcoidosis: Highly specific when seen in conjunction with the lambda sign (hilar and right paratracheal lymph node uptake)
• Lymphoma: Seen in conjunction with asymmetric hilar and mediastinal adenopathy
• Infection: Seen in conjunction with hilar and mediastinal adenopathy, especially in AIDS. Can be seen with mumps.
• Radiation sialoadenitis: Isolated panda sign
• Primary Sjögren syndrome: Isolated panda sign

Not to be confused with the panda sign of Wilson disease.

References

Mettler FA and Guiberteau MJ. Chapter 12. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 346-347.

False Positives in HIDA

False positives for acute cholecystitis may be seen with HIDA scans in the following cases:

• Non-fasting state: Meal within 2-4 hours of scan. Intermittent contractions of the gallbladder will interfere with gallbladder filling.
• Prolonged fasting: > 24 hours. Due to full gallbladder. Sincalide administration empties gallbladder and may improve sensitivity.
• Total parenteral nutrition: Thought to be due to increased bile viscosity and decreased endogenous production of cholecystokinin. Sincalide administration empties gallbladder and may improve sensitivity.
• Alcoholism: Thought to be due to increased bile viscosity and abnormal hepatobiliary function.
• Acute pancreatitis: Nonvisualization of gallbladder may be transient. Delayed imaging is needed. Etiology unknown. May be due to disturbance of gallbladder motility.
• Recent narcotic use:
• Cystic duct obstruction: For example, cholangiocarcinoma.
• Hepatocellular disease: Decreased bile production may lead to nonvisualization of the gallbladder.
• Severe chronic cholecystitis: Sincalide administration empties gallbladder and may improve sensitivity.

Sincalide (0.04 mcg/kg in 10 cc saline) administration must be slow (over 5-10 minutes) to prevent gallbladder neck spasm and less complete emptying.

Delayed images up to 4 hours reduce false positive results in cases of chronic cholecystitis. Intravenous morphine may be used to shorten the study.

References

• Edlund G, Kempi V, van der Linden W. Transient nonvisualization of the gallbladder by Tc-99m HIDA cholescintigraphy in acute pancreatitis: concise communication. J Nucl Med. 1982 Feb;23(2):117-20.
• Klingensmith WC 3rd, Turner WM. Cholescintigraphy for acute cholecystitis: false positive results caused by chronic cholecystitis. Gastrointest Radiol. 1990 Spring;15(2):129-32.
• Mettler FA and Guiberteau MJ. Chapter 8. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 222-223.
• Shuman WP, Gibbs P, Rudd TG, Mack LA. PIPIDA scintigraphy for cholecystitis: false positives in alcoholism and total parenteral nutrition. AJR Am J Roentgenol. 1982 Jan;138(1):1-5.

Metastatic Disease: Skeletal Surveys and Bone Scans

Lytic lesions must cause at least 30%-50% demineralization to be visible by radiography. Bone scan is much more sensitive in detecting metastatic lesions in some cancers, and not so great in others. Conditions that have high false negative rates on bone scan include:

• Multiple myeloma
• Renal cell carcinoma
• Thyroid carcinoma
• Langerhans cell histiocytosis
• Neuroblastoma
• Highly aggressive anaplastic tumors
• Reticulum cell sarcoma

False positivity for metastatic disease is also high when a single lesion is seen. In patients with known malignancy and no benign radiographic explanation for a bone scan lesion, additional workup is necessary. Some statistics:

• A single spinal lesion on bone scan has a 10%-20% chance of representing a metastatic focus.
• A single rib lesion on bone scan has a 10% chance of representing a metastatic focus. Lesions in consecutive ribs are almost always traumatic in origin. Lesions in nonconsecutive ribs have a high chance of representing metastatic disease.
• An isolated sternal lesion on bone scan in a patient with breast cancer, on the other hand, has an 80% chance of representing a metastatic focus.

In the case of prostate cancer, PSA level < 10 μg/L is a good predictor of a negative bone scan.

References

• Gleave ME, Coupland D, Drachenberg D, Cohen L, Kwong S, Goldenberg SL, Sullivan LD. Ability of serum prostate-specific antigen levels to predict normal bone scans in patients with newly diagnosed prostate cancer. Urology. 1996 May;47(5):708-12.
• Kwai AH, Stomper PC, Kaplan WD. Clinical significance of isolated scintigraphic sternal lesions in patients with breast cancer. J Nucl Med. 1988 Mar;29(3):324-8.
• Mettler FA and Guiberteau MJ. Chapter 9. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. p 250.
• Tumeh SS, Beadle G, Kaplan WD. Clinical significance of solitary rib lesions in patients with extraskeletal malignancy. J Nucl Med. 1985 Oct;26(10):1140-3.

Ga-citrate vs In-WBC

	67Ga-citrate	111In-WBC
Half-life	3 days	3 days
Basics	Nonspecific marker for inflammation, infection, and tumor.	Goes where the white cells go
Imaging	24-48 hours	12-24 hours
Immunocompromised patients	Great (since doesn't need inflammatory response).	OK for acute pyogenic infections. May give false negative results in viral, fungal, TB, and parasitic infections.
Uncomplicated osteomyelitis	Triple-phase bone scan is usually diagnostic. Good for following treated osteomyelitis.	Triple-phase bone scan is usually diagnostic. 111In scan with or without sulfur colloid scan can help in equivocal cases. Combined marrow (sulfur colloid)/Indium imaging. Positive: Distribution of the two tracers is spatially incongruent. Negative: Distribution of the two tracers is spatially congruent (e.g., aseptic joint loosening).
Spinal osteomyelitis/diskitis	Combined bone (diphosphonate)/Gallium imaging improves specificity. Positive: Distribution of the two tracers is spatially incongruent Positive: Distribution of the two tracers is spatially congruent and the relative intensity of gallium uptake is greater than that of diphosphonate. Negative: Distribution of the two tracers is spatially congruent and the relative intensity of gallium uptake is less than that of diphosphonate. Negative: Normal gallium scan regardless of bone scan findings Equivocal: Distribution of the two tracers is congruent both spatially and in intensity.	50% of spinal osteomyelitis are photopenic
Infected prosthesis	Combined bone (diphosphonate)/Gallium imaging has an accuracy of about 65-80%, offering modest improvement over bone scintigraphy alone.	Combined marrow (sulfur colloid)/Indium imaging sensitive and specific for osteomyelitis in cases of infected prostheses.
Post-Traumatic infection	~60% sensitivity and specificity	> 90% sensitivity and specificity
Sarcoidosis	Lambda pattern of hilar and right paratracheal adenopathy suggestive. Lambda plus panda signs together highly specific (panda=uptake in lacrimal, parotid, and salivary glands)	N/A
FUO	Chronic phase	Acute phase
Endocarditis	Not great.	Not great.
Abdominal	Not great since lots of normal bowel uptake. But good for splenic abscess, since there isn't a lot of baseline splenic activity.	Good for abdominal infections, including infected abdominal aortic grafts. Bad for splenic abscesses, since lots of baseline splenic activity (see image)
Neuropathic joint infections		In combination with bone scan. Positive early 111In images are nonspecific. Fading activity on 24-hour scans suggests sterile disease. Intense focal, incongruent activity is suggestive of infection.
Sinusitis	Not good, since there is normal nasopharyngeal uptake.	Good since no interfering nasopharyngeal uptake.

References

• Love C, Marwin SE, Palestro CJ. Nuclear medicine and the infected joint replacement. Semin Nucl Med. 2009 Jan;39(1):66-78.
• Mettler FA and Guiberteau MJ. Chapter 10. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. pp 294-295.

MAG-3 vs DTPA

	DTPA	MAG-3
Excretion	Filtration 90% extracted from blood by 4 hours	Tubular excretion (95%) and filtration (5%)
Renal function estimate	GFR May underestimate, since some DTPA is bound to plasma proteins	ERPF
Response to captopril in RAS	Decreased activity (since GFR goes down)	Increased activity (since GFR and hence tubular secretion goes down)
Parenchymal visualization	Poor due to short nephrographic phase. Even worse in patients with obstruction or renal impairment, since filtration is impaired	Good
Dose-limiting organ	Bladder	Bladder
Dose	370-740 MBq (10-20 mCi)	370-740 MBq (10-20 mCi)

The difference in excretion is important in understanding post-ACE inhibitor images. In patients with renal artery stenosis, captopril causes a decrease in GFR. If DTPA is used, there is diminished initial uptake of radiotracer with or without prolonged parenchymal transit. The latter is manifested by a delay in time to peak activity and excretion.

Since the drop in GFR doesn't affect MAG-3 uptake, there is adequate initial uptake and secretion. However, the drop in GFR results in decreased urine production and flow and decreased washout of MAG-3, resulting in cortical retention.

References

Mettler FA and Guiberteau MJ. Chapter 10. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. p 294.

Biliary Atresia and Neonatal Hepatitis: Role of Nuclear Medicine

HIDA can be used to differentiate biliary atresia from neonatal hepatitis in an infant with jaundice. Administration of 2.5-5 mg/kg phenobarbitol PO BID for 5-7 days before the study may increase diagnostic accuracy by promoting increased hepatic excretion of the radiotracer.

If biliary excretion is visualized on HIDA, biliary atresia can be excluded. Non-visualization of biliary excretion, however, cannot differentiate biliary atresia from severe neonatal hepatitis (see below). 24-hour delayed images can be obtained in such cases; however, we're fighting against the short half life of ^99mTc here and delayed imaging beyond 24 hours may not be useful.

Infants younger than 2 months with biliary atresia usually have normal hepatocyte uptake of the radiotracer. Bilirubin levels > 10 mg/dL and severe neonatal hepatitis may result in decreased hepatic radiotracer uptake and non visualization of biliary excretion, simulating biliary atresia.

References

• Mettler FA and Guiberteau MJ. Chapter 8. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. p 230.
• Zukotynski K and Babyn PS. Biliary Atresia. eMedicine. Oct 28, 2009.

Stripe Sign on V/Q Scan

The stripe sign is a band of normally perfused lung interposed between a perfusion defect and adjacent pleural surface. In the absence of other perfusion defects, it indicates a low probability for pulmonary embolism. In cases of an otherwise intermediate or low-probability V/Q scans, the stripe sign can move the diagnosis to a lower probability.

If the patient has an otherwise high-probability V/Q scan, the presence of a stripe sign does not change the diagnosis and may indicate the reperfusion of an embolic segment.

The stripe sign is most commonly seen in patients with emphysema. The stripe sign may be mimicked by shine-through of normally perfused tissue adjacent to a wedge-shaped perfusion defect in cases when only limited numbers of perfusion images are obtained. Increasing the number of projections or acquiring SPECT images may be helpful in such cases.

References

Ergün EL, Volkan B, Caner B. Stripe sign in pulmonary embolism: a review of the causes. Ann Nucl Med. 2003 Apr;17(2):145-8.

Discordant Thyroid Nodule

A thyroid nodule is considered discordant if it is hot on ^99mTc and cold on 24-hour iodine imaging. Since ^99mTc-pertechnetate is trapped but not organified, whereas iodine is both trapped and organified, a discordant nodule may either represent 1) reduced organification of iodine, or 2) rapid turnover of organified iodine.

A discordant nodule may represent benign lesions such as follicular adenoma/adenomatous hyperplasia or, in a small number of cases, thyroid cancer.

A patient with a hot nodule on ^99mTc-pertechnetate imaging should get a 24-hour iodine scan.

References

Mettler FA and Guiberteau MJ. Chapter 5. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. p 83.

Distribution of Fibromuscular Dysplasia

Fibromuscular dysplasia (FMD) has a predilection for certain arteries. The renal arteries are most commonly affected, being involved in about 60% of cases. Cervicocranial arteries (most commonly the internal carotid arteries) are involved in about 30% of cases.

Unlike atherosclerosis, stenosis of the renal arteries due to FMD is rarely ostial or proximal, but usually truncal (white arrows) or distal (pink arrows) and may involve arterial branches. Stenoses are more common on the right. Renal lesions are bilateral in about 40% of cases.

The extracranial internal carotid artery is the second most commonly affected artery. Intracranial involvement is rare, but intracranial aneurysms can be seen in about 10%-50% of patients with carotid or vertebral artery involvement.

References

• Plouin PF, Perdu J, La Batide-Alanore A, Boutouyrie P, Gimenez-Roqueplo AP, Jeunemaitre X. Fibromuscular dysplasia. Orphanet J Rare Dis. 2007 Jun 7;2:28.
• Willoteaux S, Faivre-Pierret M, Moranne O, Lions C, Bruzzi J, Finot M, Gaxotte V, Mounier-Vehier C, Beregi JP. Fibromuscular dysplasia of the main renal arteries: comparison of contrast-enhanced MR angiography with digital subtraction angiography. Radiology. 2006 Dec;241(3):922-9

Periostitis in Children

Differential diagnosis for periostitis in multiple bones:

• Physiologic periostitis: Symmetric, regular, seen at around 3 months and resolves by 6 months of age. Distal involvement in limbs (e.g., tibia) is preceded by proximal involvement (e.g., femur). Said in another way, if you see tibial involvement without femoral involvement, it's not physiologic periostitis. In the tibia, periostitis is invariably on the medial aspect. The new bone always involves the diaphysis and may extend partly into the metaphysis without extending to the end of the metaphysis.
• Child abuse: Asymmetric. Look for other signs of child abuse.
• Multifocal osteomyelitis: May be seen with congenital (TORCH, syphilis), TB, streptococcus.
• Hypervitaminosis A: Look for history of high doses of vitamin A.
• Polyostotic neoplasm: Metastases (e.g., Ewing sarcoma, medulloblastoma, neuroblastoma, osteosarcoma).
• Juvenile idiopathic arthritis: May first present with periostitis of fingers or toes with joint involvement later.
• Prostaglandin-induced neonatal periostitis: Prolonged prostaglandin therapy is associated with soft tissue swelling and reversible cortical hyperostosis in the long bones. Common side effects of short-term prostaglandin therapy include apnea, fever, convulsions, rash, skin flushing, vasodilatation with hypotension, diarrhea, and gastric outlet obstruction.
• Sickle-cell dactylitis: Initial manifestation of bone infarcts may be periostitis of fingers and toes.
• Caffey disease: Also known as infantile cortical hyperostosis. Self-limited, painful periostitis of long bones. Clavicular and mandibular involvement suggestive.
• Scurvy: Subperiosteal hemorrhage with corner fracture leads to periosteal elevation and reparative bone formation that mimics periosteal reaction.
• Primary Hypertrophic Osteoarthropathy: About 80% present before 18 years or age, and the disease stabilizes after about 5–20 years.

PERIOSTEAL SOCKS, an idiotic mnemonic that is too long to be of any practical use, includes many of the above entities: Physiologic/Prostaglandin, Eosinophilic granuloma (properly called Langerhans cell histiocytosis under the new classification of histiocytic disorders), Rickets, Infantile cortical hyperostosis, Osteomyelitis, Scurvy, Trauma, Ewing, A-hypervitaminosis, Leukemia & neuroblastoma, Syphilis, Osteosarcoma, Child abuse, Kinky hair syndrome, and Sickle cell disease.

See related post on periostitis in adults.

References

• StatDx
• de Almeida JF, Kimura H, Hercowitz LH, Korkes H, Troster EJ. Cortical hyperostosis secondary to prolonged use of prostaglandin E1. Clinics (Sao Paulo). 2007 Jun;62(3):363-6.
• de Silva P, Evans-Jones G, Wright A, Henderson R. Physiological periostitis; a potential pitfall. Arch Dis Child. 2003 Dec;88(12):1124-5.

Colonic Angiodysplasia

Colonic angiodysplasia is the second most common cause colonic arterial bleeding in patients over 50 years of age (later than diverticulosis). They are found most commonly on the right and are characterized by clusters of dilated thin-walled veins in the submucosa.

Hemorrhage from angiodysplasia is episodic, making specific localization by extravasation of contrast media the exception rather than the rule. Angiography will show a cluster of small arteries during the arterial phase along the antimesenteric border of the colon. There will be accumulation of contrast material in vascular spaces and intense opacification of the bowel wall during the capillary phase followed by early opacification of dilated draining veins that persists late into the venous phase.

For some reason, bleeding from angiodysplasia is associated with aortic stenosis, a complex referred to as Heyde syndrome. More strange still, bleeding usually stops after aortic valve replacement. It has been suggested that this has to do with acquired type IIA von Willebrand syndrome, a deficiency of high-molecular-weight multimers of von Willebrand factor.

References

• Baum S, Athanasoulis CA, Waltman AC, Galdabini J, Schapiro RH, Warshaw AL, Ottinger LW. Angiodysplasia of the right colon: a cause of gastrointestinal bleeding. AJR Am J Roentgenol. 1977 Nov;129(5):789-94.
• Warkentin TE, Moore JC, Morgan DG. Gastrointestinal angiodysplasia and aortic stenosis. N Engl J Med. 2002 Sep 12;347(11):858-9.

Sinotubular Ridge

The sinotubular ridge the portion of the ascending aorta just distal to the sinuses of Valsalva at the junction with the tubular segment of the ascending aorta.

Dilation of the aortic valve and effacement of the sinotubular ridge is characteristic of Marfan syndrome and other connective disorders, while one of the characteristic features of syphilitic aneurysm is sparing of the sinotubular junction

Aortic sinotubular ridge calcification may be associated with coronary artery disease.

References

• Kaufman JA and Lee MJ. Chapter 9. in Vascular and interventional radiology: The Requisites. Mosby 20004. pp 229-230.
• Stechert MM, London MJ. Aortic sinotubular ridge calcification: a common transesophageal echocardiography finding with uncertain implications. Anesth Analg. 2009 Jul;109(1):32-4.

Spina Ventosa

Spina ventosa ("wind-filled sail") refers to the end-stage radiographic appearance of tuberculosis dactylitis: Cystic expansion of the short tubular bones with bone destruction.

Tuberculous dactylitis is the painless tuberculous involvement of the fingers and toes and is more common in children. It begins with fusiform soft-tissue swelling with or without periostitis.

Differential considerations include: pyogenic or fungal infections, leukemia, sarcoidosis, hemoglobinopathies, hyperparathyroidism, and syphilis.

An image of spina ventosa can be found at the RadioGraphics article cited below.

References

Engin G, Acunaş B, Acunaş G, Tunaci M. Imaging of extrapulmonary tuberculosis. Radiographics. 2000 Mar-Apr;20(2):471-88; quiz 529-30, 532.