November 30, 2010

Leptomeningeal Enhancement

Sagittal T1W MR image post gadolinium shows extensive leptomeningeal enhancement (arrrows) along the cerebral sulci and cerebellar folia.

Differential Diagnosis:
  • Leptomeningeal carcinomatosis: usually due to breast or lung metastasis, or primary CNS tumor. In children, the most common cause is medulloblastoma.
  • Meningitis (bacterial, tuberculosis, coccidiodomycosis)
  • Neurosarcoidosis: often involves the basal cistern
Facts: Leptomeningeal Carcinomatosis
  • Hematogenous spread of malignancy (i.e., breast, lung) or direct extension by CNS tumor
  • MRI with contrast administration best imaging tool to detect this abnormality, much more sensitive than CT
  • Imaging Findings: smooth or nodular enhancement along the leptomeninges (extending into sulci), hyperintensity of sulci on FLAIR, hydrocephalus (which may be the only sign seen on CT)
Our case: Leptomeningeal carcinomatosis from esophageal cancer

1. O'Brien WT. Top 3 differentials in radiology: a case review, 2009.
2. Lev MH, Heisserman J, Shetty S. Q&A color review of neuroimaging, 2008.

November 27, 2010

PET/CT and Breast Cancer

A coronal fused PET/CT image shows a large right breast mass with a ring-like FDG uptake (arrows).

Performance of PET in Breast Cancer
  • Sensitivity 89%, specificity 80%
  • Sensitivity highly depends on tumor size and grade. Unlikely to pick up tumor less than 0.5 cm, low chance of detecting tumor less than 1 cm
  • PET is less sensitive but more specific than MRI for characterizing and detecting breast lesions
  • Any focal abnormal uptake of FDG should undergo further work-up (irrespective of its standardized uptake value). Note that breast cancer, in general, has lower metabolic activity than most other malignancies
  • Incidentally detected breast abnormality on PET has high likelihood of malignancy
  • Delayed/dual time point imaging increases sensitivity and accuracy of PET. Tumors accumulate FDG over time (normal breast tissue will not)
Differential Diagnosis of Focal FDG Uptake in the Breast
  • Inflammatory: abscess, soft tissue inflammation, TB, sarcoidosis
  • Trauma: post-biopsy, hematoma, seroma
  • Benign neoplasms: ductal adenoma, fibrous dysplasia, fibroadenoma (rare)
Our case: spindle cell sarcoma of the breast.

Lin EC, Alavi A. PET and PET/CT a clinical guide, 2nd edition, 2008.

November 24, 2010

National Lung Screening Trial (NLST) Initial Results

What is the NLST?
  • A multicenter, randomized controlled trial (RCT) comparing low-dose helical CT with standard chest radiography in the screening of men and women at risk for lung cancer
  • Sponsored by the National Cancer Institute
  • Starting in August 2002, the trial enrolled more than 53,000 participants, current or former heavy smokers, ages 55 to 74, at 33 sites over a 20 month period
  • Participants were randomly assigned to received 3 annual screens with either low-dose helical CT or standard chest radiograph. Endpoint = death from lung cancer
  • "Heavy smoker" = at least 30 pack-years and were either current or former smokers without signs, symptoms or history of lung cancer
  • "Low-dose CT" = helical CT with 120-140 kVp, 40-80 mAs, detector collimation equal to or less than 2.5 mm
Findings To Date
  • 354 deaths from lung cancer among participants in the CT arm of the study, v.s. 442 lung cancer deaths in the chest radiograph arm. 20% reduction in lung cancer mortality among participants screened with low-dose helical CT.
  • All-cause mortality (deaths due to any factor) was 7% lower in those screened with low-dose CT than in those with chest radiograph

National Lung Screening Trial Research Team. The National Lung Screening Trial: overview and study design. Radiology 2010, published online before print on November 2, 2010.

November 21, 2010

Contrast Agents for Liver MRI

Gadolinium Chelates
  • Most commonly used contrast agent
  • Standard dose 0.1 mmol Gd/kg
  • Bolus injection, dynamic study during arterial (20-30s) to detect hypervascular lesions, portovenous phase (60-90s) to detect hypovascular lesions, and equilibrium phase (between 2-10 min) to allow hemangiomas to fill-in and cholangiocarcinoma and inflammation to enhance
Liver-Specific Agents
  • Teslascan (Mn-DPDP)
  • MultiHance (gadobenate dimeglumine)
  • Primovist (gadoxetic acid)
  • SPIO (Endorem/Feridex)
  • Hepatocyte-specific MR contrast agent
  • Uptake into hepatocyte and partially excretes into the bile
  • Drip infusion
  • Increased T1 signal intensity
  • Differentiate tumors of hepatocellular origin from nonhepatocellular origin
  • 4% biliary excretion
  • Can be bolus injected, images also taken 1-2 hours later for tumor detection (uptake into liver parenchyma to increase conspicuity of metastases)

  • Strong biliary excretion
  • Can be bolus injected (doses 0.025 mmol/kg), images on delayed phase can be taken as early as 20 min
Superparamagnetic Iron Oxide Particles (SPIO)
  • Accumulates within phagocytes in the liver (typically, there is absence of phagocytes in malignancy)
  • On T2WI, normal tissues or lesions with phagocytes (ie, FNH, hepatocellular adenoma, well-differentiated HCC) appear dark
  • Drip infusion
  • Imaging done several hours after contrast administration
Above image: gadolinium metal, from

Reimer P, Parizel PM, Meaney JFM, Stichnoth FA. Clinical MR Imaging, 2010

November 18, 2010

ACR Appropriateness Criteria on Colorectal Cancer Screening

Rationale for Colorectal Cancer Screening
  • Colorectal cancer is the 2nd leading cause of cancer death in the USA
  • Treatment for localized disease is associated with high survival rate
  • Almost all colorectal cancers develop from benign adenomas and this process is slow (average of 10 years)
Current Screening Recommendation
  • By WHO, US Agency for Health Care Policy and Research, US Preventive Service Task Force: 4 options = annual or biennial fecal occult blood test (FOBT), flexible sigmoidoscopy every 5 years, double-contrast barium enema (DCBE) every 5 years, and colonoscopy every 10 years
  • By the American Cancer Society (jointly issued with the US Multi-Society Task Force on Colorectal Cancer and the ACR): adding CT colonography (CTC) every 5 years as an option
ACR Appropriateness Criteria Rating
  • Average-risk individual, age greater than 50 years: CTC every 5 years after negative screen (rate 8), DCBE every 5 years after negative scan (rate 7)
  • Average-risk individual after positive FOBT indicating relative elevation in risk: CTC every 5 years after negative scan (rate 8), DCBE every 5 years after negative scan (rate 7)
  • Individual of any risks after incomplete colonoscopy: CTC (rate 9), DCBE (rate 7)
  • High-risk individual with hereditary nonpolyposis colorectal cancer, ulcerative colitis or Crohn's colitis: colonoscopy preferred for ability to obtain biopsies to look for dysplasia
Yee J, Rosen MP, Blake MA, et al. ACR appropriateness criteria on colorectal cancer screening. JACR 2010; 7:670-678.

November 15, 2010

Bennett's Fracture Dislocation

  • Most frequent fracture at the base of the first metacarpal
  • Fracture dislocation resulting from axial loading to a partially flexed thumb (i.e., in a fist fight)
  • Oblique fracture involves the carpometacarpal joint, resulting in a volar fragment attached to the trapezium and the distal metacarpal fragment displacing proximally/radially/dorsally by pull of abductor pollicis longus
  • First CMC joint is a saddle-shaped bone, any minor malalignment results in substantial articular incongruity. This fracture dislocation frequently requires open reduction and fixation
  • Oblique fracture line with a triangular fragment at the first metacarpal base
  • Proximal displacement of the metacarpal
  • Important to note the size of the triangular volar fragment and the degree of displacement of the metacarpal fragment

1. Robinson P. Essential Radiology for Sports Medicine, 2010.
2. Bennett's Fracture Dislocation. Wheeless' Textbook of Orthopedics

November 12, 2010

Abdominal Wall Fibromatosis

An axial T2W MR image of a 32-year-old woman shows a large well-defined heterogeneous mass in the anterior abdominal wall involving the right rectus abdominis. There are a few linear band (arrowheads) of low signal intensity with in the mass, which are seen in all pulse sequences.

  • Also known as abdominal desmoid
  • Predilection to develop in women of child-bearing age (usually 20-30 years)
  • Mass in abdominal wall typically develops following pregnancy
  • Most common muscle involved: rectus abdominis, internal oblique
  • Some of the masses have estrogen receptor
  • May be seen as a manifestation of Gardner's syndrome
  • Rx = surgical removal but recurrence rate 15-40%
Imaging Findings
  • Heterogeneous intramuscular mass (well- or ill-defined)
  • Non-enhancing bands of low signal within the mass on all pulse sequences (probable fibrosis)
  • Linear fascial extension "fascial tail sign"

Kransdorf MJ, Murphy MD. Imaging of soft tissue tumors, 2nd ed, 2006.

November 9, 2010

Jefferson Fracture

Axial CT image shows double fractures of the anterior arch and a single fracture of the posterior arch of atlas (C1) (arrows) with mild displacement.

  • C1 fracture believed to be due to compression causing fracture of the arch of atlas
  • Often in combination with avulsion of the transverse ligament of the C1
  • Simultaneous injuries to other C spine are common
  • Three types: fracture of only anterior arch (type 1), fracture of only posterior arch (type 2), and fractures of both anterior and posterior arches (type 3)
  • Type 3 fracture is unstable
  • Fractures rare in children, but one needs to know that anterior synchondroses fuse at age 7, posterior at age 4.
Imaging Findings
  • MDCT is imaging modality of choice, able to demonstrate fracture lines and degree of displacement
  • On radiograph, displacement of the lateral masses may be seen on the odontoid view.
  • Mimicker = failure of fusion of the vertebral arch, this pseudo-fracture lines are less sharply defined and/or sclerotic.
1. Imhof H, et al. Spinal Imaging, 2008.
2. Atlas Frx / Jefferson Fracture in Wheeless' Textbook of Orthopedics

November 6, 2010

Caval Index

Longitudinal ultrasound images of the IVC in an asymptomatic patient demonstrate a normal inferior vena cava (IVC) during inspiration and expiration, in which the diameters (yellow double-headed arrows) do not change significantly. In this case, the diameters of the IVC were measured 2-3 cm below the right atrial border (yellow lines).

Facts: IVC Diameter
  • IVC diameter changes following total body volume (increases with increasing total body volume, and decreases with volume depletion)
  • IVC normally collapses with inspiration (decreased intra-thoracic pressure) and expands with expiration (but this collapsibility should not exceed 50%)
Caval Index
  • Caval Index = 100 x (diam expiration - diam inspiration)/diam expiration
  • Where to measure the IVC? Several ways exist, and none is perfect yet. Easy way is to measure with a longitudinal view of the IVC - find the junction of the atrium and IVC and measure the IVC at 2-3 cm below the junction
  • Interpretation: studies vary greatly as to significance of values in different patient populations. In general, if caval index is greater than 50% it suggests low central venous pressure (CVP less than 8 mmHg) and high probability of fluid responsiveness
Nagdev AD, Merchant RC, Tirado-Gonzalez A, et al. Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann Emerg Med 2010; 55:290-295.

November 1, 2010

Anastomotic Leakage After Bowel Surgery

Two coronal-reformatted CT images of the abdomen show a localized fluid collection (arrows) in the right abdomen, which contains air bubbles, fluid and oral contrast material, in a patient who had recent small bowel resection.

Facts: Anastomotic Disruption
  • One of the most fearful complication after intestinal surgery
  • Can present early or late. The latter can be difficult to distinguish from other postoperative infectious complications
  • In a prospective study of 1223 patients who had intestinal resection and anastomosis without fecal diversion, the incidence of anastomotic leak was 2.7%.
  • Location of anastomosis is among the most significant factors associated with leak. Those in the pelvis have a higher rates of leakage
  • Clinical presentation: pain, tachycardia, high fevers, rigid abdomen accompanied by hemodynamic instability. Typically, leak is discovered 5-7 days after surgery.
  • CT is helpful to determine whether there is an associated abscess. Gastrograffin enema may aid the diagnosis of leak.
  • Visualization of administered contrast (on CT or enema) is the direct sign of anastomotic leak. Neither CT nor enema is perfect to show the leak, unfortunately.
  • Many CT features of postoperative bowel overlap between patients with and without a leak. The most specific feature of a leak is the presence of extraluminal contrast.
1. Hyman N, Manchester TL, Osler T, Burns B, Cataldo PA. Anastomotic leaks after intestinal anastomosis. Ann Surg 2007; 245:254-258.
2. Mulholland MW, Doherty GM. Complications in Surgery, 2005.