November 29, 2008

Avulsion Fracture of Base of 5th Metatarsal & Os Peroneum

Figure: Oblique radiograph of the foot shows a transverse avulsion fracture (arrow) of the 5th metatarsal bone with displacement and extension into the cuboid-metatarsal joint. Note a nearby 'os peroneum' (arrowhead).

Avulsion Fracture of Base of 5th Metatarsal

  • Most common fracture at this location
  • Usually extra-articular
  • Due to sudden contraction of peroneus brevis muscle or lateral band of plantar fascia during inversion
  • Treated conservatively, unless there is displacement or large fragment involving cuboid-metatarsal joint
  • Other two types of fractures (at proximal 5th metatarsal) are Jones (AKA fracture at metadiaphyseal junction within 1.5 cm distal to tuberosity of 5th metatarsal), and stress fracture.
Key Things to Include in Report
  1. Location (tip, tuberosity, metadiaphyseal junction, diaphysis)(to distinguish between different types of proximal 5th metatarsal fractures)
  2. Joint involvement (cuboid-metatarsal, 4th-5th intermetatarsal)
  3. Displacement
Os Peroneum = ossicle in peroneus longus, seen at the tip of 5th metatarsal base, common

Nunley JA. Fractures of the base of the fifth metatarsal. Orthopedic Clinics of North America (January 2001)

November 26, 2008

A child with scalp mass

Sagittal T1W image demonstrates a parieto-occipital scalp mass with a band of soft tissue anterosuperior to the mass running through a small skull defect which appears to connect to the intracranial compartment.

Sagittal T2W image demonstrates a persistent embryonic falcine sinus/vertically oriented straight sinus and prominence of the superior cerebellar cistern.

The mass shows a thin peripheral enhancement as well as enhancement of the soft tissue band.

Atretic (en)cephalocele
- A midline mass typically parietal in location, occasionally seen in occipital region.
- Contain meninges and neural rests. A fibrous stalk connects the lesion to the dura.
- A vertically positioned straight sinus/persistent embryonic falcine sinus commonly
associated with these malformations. Anomalies of the tentorial incisura and superior sagittal
sinus have also been reported.
- Associated intracranial anomalies are variable, and some children may have normal clinical outcomes with no associated intracranial anomalies

AJNR Am J Neuroradiol 19:791–795, April 1998
RadioGraphics 2004; 24:1655–1674

November 24, 2008

Nipple Shadows?

Fig.1: Chest radiograph shows a suspicious nodule in the right lower lung. Fig.2: Repeat exam with nipple markers (arrowheads) confirmed the nodule to be a nipple shadow. Note that the left nipple shadow is visualized on this exam but not on the previous one performed on the same date.

Classic Nipple Shadows

  • Bilateral symmetric
  • Fuzzy margins with radiolucent halo, or sharp lateral but poorly defined medial margins
  • Characteristic location (fifth or sixth anterior ribs or near bottom of breast shadow)
  • Not present on a very recent film
  • Could be identified on lateral film
  • Nipple shadows can be seen in up to 10% of chest radiographs
  • Although most of these can be resolved as 'classic nipple shadows' and no further imaging is needed, about 1.4% need repeat examination
  • Repeat examinations are related to increased cost, time and burdensome to patients
Nipple Markers
  • A 1.5 mm lead shot that, given its size, should not obscure a true pulmonary nodule
  • Very helpful to determine whether the suspicious nodule is actually a nipple shadow, or not.
  • Chance of having a true pulmonary nodule lying beneath the nipple shadow is very slim
Miller WT, et al. The troublesome nipple shadow. AJR 1985 (September)

November 21, 2008

Gastric Cancer on CT

Figure: Axial CT shows thickening (arrows) and mucosal enhancement of the lesser curvature of the stomach in a patient with known gastric carcinoma. The fat plane is preserved. No lymphadenopathy is seen.

Gastric Carcinoma

  • Etiology: atrophic gastritis, adenomatous polyp, Lynch syndromes, gastric stump cancer, Menetrier's disease
  • Usually present in advanced stage
  • Major determination of staging of gastric carcinoma = extent of tumor beyond gastric wall and lymph node involvement
  • CT usually used to determine presence and extent of perigastric spread
Gastric Carcinoma on CT
  • Wall thickening, soft tissue mass (polypoid or ulcerated mass), perigastric fat stranding, lymphadenopathy
  • Differentiation from lymphoma: lymphoma usually has a very thick wall, no perigastric stranding, and bulky lymph nodes
  • CT accuracy for staging is better with multiplanar reformations (coronal and sagittal), better for T staging than N staging
T Staging by CT
  • T1 lesion = focal thickening of the inner layer of the wall
  • T2 lesion = transmural thickening of the wall without or with minimal perigastric stranding
  • T3 lesion = blurring of at least 1/3 of tumor extent or wide reticular stranding around tumor border
  • T4 lesion = invasion of adjancent organ or fat plane obliteration between tumor and adjacent organ
  • Accuracy based on this description was 77% in one study, when axial + MPR images were used
Hur J, et al. Diagnostic accuracy of multidetector row computed tomography in T- and N staging of gastric adenocarcinoma with histopathologic correlation. J Comput Assist Tomogr 2006 (May/June)

November 18, 2008

Calcium Pyrophosphate Dihydrate (CPPD) Crystal Deposition Disease of the Wrist

Fig. Frontal radiograph of the wrist shows calcifications of the lunotriquetral ligament (arrowhead) and triangular fibrocartilage (red arrow). Joint space narrowing with sclerosis of the trapezioscaphoid and carpometacarpal joints (yellow arrows) are noted. Note absence of osteophytes.

This patient presents with classic radiographic features of CPPD, which include:

  1. Chondrocalcinosis
  2. Degenerative change without apparent osteophytosis
  • At the wrist, the most common location of calcification in the area of triangular fibrocartilage is at the lunotriquetral ligament > triangular fibrocartilage > lunotriquetral cartilage.
  • Degenerative change in CPPD differs from osteoarthritis in that there is less osteophyte formation.

1. Yang B, et al. Distribution of calcification in the triangular fibrocartilage region in 181 patients with calcium pyrophosphate dihydrate crystal deposition disease. Radiology 1995; 196:547.
2. Saffar P. Chondrocalcinosis of the wrist. J Hand Surg [Br] 2004; 29:486.

November 15, 2008

Colon Cutoff Sign

Fig. 1: Supine abdominal radiograph in a 30-year-old man with acute abdominal pain shows gas in the transverse colon (C) with an abrupt termination at the level of splenic flexure (arrowheads). The more distal colon is decompressed. S = stomach
Fig. 2: Axial CT image of the same patient (done a few hrs later) shows extensive inflammation and necrosis of the pancreas (arrows) with free fluid in the abdomen (stars).

What is Colon Cutoff Sign?
Abrupt termination of gas in proximal colon at the level of the splenic flexure.
Applied to radiography, CT and contrast enema studies

What Can Cause Colon Cutoff Sign?

  • Most common = acute pancreatitis
  • True colonic obstruction e.g. colonic malignancy
  • Other causes of colonic inflammation
Why Does It Occur?
In acute pancreatitis, inflammatory exudates in retroperitoneal space extend into 'phrenicocolic ligament' causing spasm of the splenic flexure wherer the colon returns to retroperitoneum. (Remember - transverse colon in peritoneal cavity, descending colon in retroperitoneum, phrenicocolic ligament is a transition point where transverse and descendinc colon is separated)

Available in Podcast (Thai language only): website | iTunes

Pickhardt P. The colon cutoff sign. Radiology 2000;215:387.

November 12, 2008

Metformin and Iodinated Contrast Agents

Facts about Metformin

  • Medication for treatment of type II diabetes
  • Decreases hepatic glucose production and enhance glucose uptake in peripheral tissues (by increase insulin sensitivity)
  • May be in a pure form or in combination with other antihyperglycemic drugs
  • Renal excretion
  • Most significant reaction is lactic acidosis, which has a high mortality (up to 50%)
  • Most metformin associated lactic acidosis (MALA) occured in patients with coexisting renal dysfunction (high level of metformin due to poor excretion)
Why Do We Worry About Metformin and Iodinated Contrast Agents?
  • The use of iodinated contrast agents in patients with pre-existing renal dysfunction can lead to significant contrast-induced nephropathy - that could, in turn, worsen MALA.
In Whom We Should Worry?
  • Patients with pre-existing renal dysfunction
  • Patients with comorbidities that could give rise to lactic acidosis (liver dysfunction, alcohol abuse, heart failure, myocardial ischemia, peripheral muscle ischemia, sepsis, severe infection)
What To Do?
  • Patients with normal renal function and no known comorbidities -> no need to discontinue metformin prior to IV contrast administration
  • Patients with known comorbidities -> Discontinue metformin at time of IV contrast administration, and withheld for 48 hours
  • Patients with known renal dysfunction -> suspend metformin at time of IV contrast administration, renal function follow-ups until safe reinstitution of metformin can be assured
American College of Radiology. Manual on Contrast Media version 6 (2008).

McCartney MM, et al. Metformin and contrast media - a dangerous combination? Clin Radiol 1999;54:29.

November 9, 2008

When to Obtain Ankle Radiographs

- Ankle radiography was the third most common study ordered in the emergency department.
- Majority of patients with ankle radiographs did not receive adequate physical examination before radiographs were obtained.
- Only 17% of extremity radiographs obtained had abnormality that would alter treatment.

Guidelines for Obtaining Ankle Radiographs (Ottawa Rule)

  1. Inability to bear weight immediately after the injury OR
  2. Point tenderness (over medial malleolus, posterior edge or inferior tip of lateral malleolus, talus, calcaneus) OR
  3. Inability to ambulate for four steps in the emergency room
Sensitivity approaches 100% in excluding significant ankle fractures
Decrease number of ankle and midfoot radiographs by 19% - 36%

Podcast of this post is available in iTunes Store or a website.

ACR Appropriateness Criteria "Suspected Ankle Fracture", revised 2005.

November 6, 2008

Air-Fluid Levels at Different Heights in the Same Loop of Bowel

Upright abdominal radiograph of the same patient shows multiple air-fluid levels in the small bowel. Note 'different heights of air-fluid levels in the same loop' (arrows). SB = small bowel, C = colon.

Differential Air-Fluid Levels

  • Two distinct air-fluid interfaces on an upright abdominal radiograph that are at different heights but within the same loop of bowel.
  • Once believed to be strongly suggestive of mechanical small bowel obstruction (due to ongoing peristalsis against mechanical blockage BUT it can be found in both mechanical obstruction and ileus (in one series, 50% of mechanical obstruction and 29% of ileus)
  • Helpful to suggest mechanical small bowel obstruction if a differential air-fluid level is 2 cm or greater (however, not the other way around!) with a reasonable positive predictive value (PPV). As height increases, PPV and specificity increases.
  • Differential height of 2.5 cm or greater is suggestive of high-grade small bowel obstruction.
This case: partial, low-grade small bowel obstruction, likely due to adhesion (history of multiple previous abdominal surgery).

1. Harlow CL, et al. Diagnosis of bowel obstruction on plain abdominal radiographs: significance of air-fluid levels at different heights in the same loop of bowel. AJR Am J Roentgenol 1993;161:291.
2. Lappas JC, et al. Abdominal radiography findings in small bowel obstruction: relevance to triage for additional diagnostic imaging. AJR Am J Roentgenol 2001;176:167.

November 3, 2008

Preseptal Cellulitis

Axial contrast-enhanced CT image of the orbit shows soft tissue thickening of the right preseptal region (between arrows). The retroorbital fat is normal (arrowheads).


  • 'Periorbital' or 'preseptal' infection = infection of tissues anterior to orbital septum.
  • Orbital septum separates preseptal space from orbit. Orbital septum is a connective tissue extension of periosteum reflected into upper and lower eyelids. It serves as a barrier to spread of infection to the orbit.
  • Most common cause of preseptal cellulitis is localized infection of eyelid or adjacent structures (mostly due to S. aureus)

1. Wald ER. Periorbital and orbital infections. Infect Dis Clin N Am 2007;21:393.
2. Lui I, et al. Preseptal and orbital cellulitis: a 10-year review of hospitalized patients. J Chin Med Assoc 2006;69:415.