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

References:

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.

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

Pearls

• 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.

Reference:

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

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

Reference:

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.

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)

Teslascan

• 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

MultiHance

• 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)

Primovist

• 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 www.emovendo.net

Reference:

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

Reference:

Yee J, Rosen MP, Blake MA, et al. ACR appropriateness criteria on colorectal cancer screening. JACR 2010; 7:670-678.

Bennett's Fracture Dislocation

Facts:

• 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

Imaging

• 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

References:

1. Robinson P. Essential Radiology for Sports Medicine, 2010.

2. Bennett's Fracture Dislocation. Wheeless' Textbook of Orthopedics

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.

Facts:

• 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"

Reference:

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

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.

Facts:

• 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.

References:

1. Imhof H, et al. Spinal Imaging, 2008.

2. Atlas Frx / Jefferson Fracture in Wheeless' Textbook of Orthopedics

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

Reference:

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.

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.

Imaging

• 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.

Reference:

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.