CT Interpretation: Abdomen/Pelvis

As with the systematic approach preferred for the evaluation and management of other processes explored on this site, a similarly structured method for the interpretation of imaging commonly obtained in the emergency department may afford the same benefits – namely, the timely identification of pathology while avoiding costly missed diagnoses. In this post, I propose an approach to the interpretation of computed tomography of the abdomen and pelvis.

Aorta Down

Thoracic Aorta

Thoracic Aorta

Start with the descending thoracic aorta

Abdominal Aorta

Abdominal Aorta

Follow the abdominal aorta down including its branches (celiac, SMA, paired renal arteries, IMA)

Aortic Bifurcation

Aortic Bifurcation

Continue to the bifurcation of the abdominal aorta to the left and right common iliac arteries

Veins Up

Femoral Veins

Femoral Veins

Start with the left and right femoral veins

Inferior Vena Cava

Inferior Vena Cava

Follow the inferior vena cava up

Infrahepatic IVC

Infrahepatic IVC

The inferior vena cava gains contrast from the renal veins

Right Atrium

Right Atrium

The inferior vena cava empties into the right atrium

Solid Organs Down

Heart and Pericardium

Heart and Pericardium

Evaluate for the presence of a pericardial effusion or cardiomegaly

Spleen

Spleen

Heterogenous contrast-enhancement is normal

Pancreas

Pancreas

The tail of the pancreas lies in the hilum of the spleen

Liver

Liver

Evaluate the intrahepatic bile ducts for dilation or pneumobilia, portal venous system for gas, and liver parenchyma for vascular abnormalities or abscesses

Gallbladder

Gallbladder

Evaluate for radioopaque stones, pericholecystic fluid or surrounding fat stranding

Adrenal

Adrenal

A wishbone-shaped structure superior to the kidneys

Kidney and Ureter

Kidney and Ureter

Evaluate for hydronephrosis or hydroureter

Bladder

Bladder

Continue down into the pelvis; in a female patient the evaluation should include the uterus and adnexa

Rectum Up

Rectum

Rectum

Having reached the inferior-most portion of the image following solid organs, move upward again from the rectum

Sigmoid

Sigmoid

Evaluate the sigmoid colon for diverticulitis

Transverse

Transverse

Continue following the sigmoid colon up the descending colon to the transverse colon and the hepatic flexure

Cecum

Cecum

Continue down the ascending colon to the cecum

Appendix

Appendix

At the cecum, attempt to identify a small tubular structure (the appendix) - evaluate for periappendiceal fat stranding, perforation or abscess

Esophagus Down

Esophagus

Esophagus

Start at the esophagus, evaluate for perforation or hernia

Stomach

Stomach

Continue to the stomach and duodenum

Small Bowel

Small Bowel

Evaluate the small bowel for obstruction (dilation, air-fluid levels)

Tissue-specific Windows

Lung Window

Lung Window

Switch to lung window to evaluate the lung parenchyma and continue through the abdomen to identify intraperitoneal free air

Bone Window

Bone Window

Use the bone window to identify fractures or lytic lesions

Try It Yourself

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CT Abdomen/Pelvis Interpretation

  • Cystic lesion in the inferior right lobe of the liver most consistent with hepatic abscess.
  • Multiple calcified gallstones in the gallbladder.

Hypotension

Brief H&P:

A 50 year-old male with a history of colonic mucinous adenocarcinoma on chemotherapy presented with a chief complaint of “vomiting”. He was unwilling to provide further history, repeating that he had vomited blood prior to presentation. His initial vital signs were notable for tachycardia. Physical examination showed some dried vomitus, brown in color, at the nares and lips; left upper quadrant abdominal tenderness to palpation; and guaiac-positive stool. Point-of-care hemoglobin was 3g/dL below the most recent measure two months prior. As his evaluation progressed, he developed hypotension and was transfused two units of uncrossmatched blood with adequate blood pressure response – he was started empirically on broad-spectrum antibiotics for an intra-abdominal source. Notable laboratory findings included a normal hemoglobin/hematocrit, acute kidney injury, and elevated anion gap metabolic acidosis presumably attributable to serum lactate of 10.7mmol/L. Computed tomography of the abdomen and pelvis demonstrated pneumoperitoneum with complex ascites concerning for bowel perforation. The patient deteriorated, was intubated, started on vasopressors and admitted to the surgical intensive care unit. The initial operative report noted extensive adhesions and perforated small bowel with feculent peritonitis. He has since undergone multiple further abdominal surgeries and remains critically ill.

Imaging

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CT Abdomen/Pelvis

Free air is seen diffusely in the non-dependent portions of the abdomen: in the anterior abdomen and pelvis, inferior to the diaphragm, and in the perisplenic region. There is complex free fluid in the abdomen.

Algorithm for the Evaluation of Hypotension1

This process for the evaluation of hypotension in the emergency department was developed by Dr. Ravi Morchi. In the case above, a systematic approach to the evaluation of hypotension using ultrasonography and appropriately detailed physical examination may have expedited the patient’s care. The expertly-designed algorithm traverses the cardiovascular system, halting at evaluable checkpoints that may contribute to hypotension.

  1. The process begins with the cardiac conduction system to identify malignant dysrhythmias (bradycardia, or non-sinus tachycardia >170bpm), which, in unstable patients are managed with electricity.
  2. The next step assesses intravascular volume with physical examination or bedside ultrasonography of the inferior vena cava. Decreased right atrial pressure (whether due to hypovolemia, hemorrhage, or a distributive process) is evidenced by a small and collapsible IVC. If hemorrhage is suspected, further ultrasonography with FAST and evaluation of the abdominal aorta may identify intra- or retroperitoneal bleeding.
  3. If a normal or elevated right atrial pressure is identified, evaluate for dissociation between the RAP and left ventricular end-diastolic volume. This is typically caused by a pre- or intra-pulmonary obstructive process such as tension pneumothorax, cardiac tamponade, massive pulmonary embolism, pulmonary hypertension, or elevated intra-thoracic pressures secondary to air-trapping. Thoracic ultrasonography can identify pneumothorax, pericardial effusion, or signs of elevated right ventricular systolic pressures (RV:LV, septal flattening).
  4. Assuming adequate intra-vascular volume is arriving at the left ventricle, rapid echocardiography can be used to provide a gross estimate of cardiac contractility and point to a cardiogenic process. If there is no obvious pump failure, auscultation may reveal murmurs that would suggest systolic output is refluxing to lower-resistance routes (ex. mitral insufficiency, aortic insufficiency, or ventricular septal defect).
  5. Finally, if the heart rate is suitable, volume deficits are not grossly at fault, no obstructive process is suspected, and cardiac contractility is adequate and directed appropriately through the vascular tree, the cause may be distributive. Physical examination may reveal dilated capillary beds and low systemic vascular resistance.

Algorithm for the Evaluation of Hypotension

References

  1. Morchi R. Diagnosis Deconstructed: Solving Hypotension in 30 Seconds. Emergency Medicine News. 2015.

Aortic Dissection

Imaging

Prominent cardiomediastinal silhouette, which may be due to patient position.

Prominent cardiomediastinal silhouette, which may be due to patient position.

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CT Angiography Aorta

Highly complex type B aortic dissection originating at the distal arch (just distal to the left subclavian artery) and terminating at the level of diaphragm. The dissection contains multiple false lumens containing blood products of differing ages (thrombus and contrast-opacified blood). No apparent involvement of the left common carotid or left subclavian artery.

Mediastinum Anatomy

Mediastinal Masses

Anterior
Retrosternal goiter
Thymoma
Germ-cell tumor
Lymphadenopathy (lymphoma)
Middle
Aortic arch aneurysm
Dilated pulmonary artery
Tracheal lesion
Posterior
Esophageal lesions
Hiatal hernia
Descending aortic aneurysm
Paraspinal abscess

References:

  1. Faiz, O., & Moffat, D. (2002). Anatomy at a glance. Malden, MA: Blackwell Science.
  2. Whitten CR, Khan S, Munneke GJ, Grubnic S. A diagnostic approach to mediastinal abnormalities. Radiographics. 2007;27(3):657–671. doi:10.1148/rg.273065136.
  3. WikEM: Widened mediastinum

Ultrasound Gallery

Appendicitis

Appendicitis

Non-compressible tubular structure in the RLQ of a patient with focal abdominal tenderness. >6mm in diameter.

Common Bile Duct

Common Bile Duct

A tubular structure typically anterior to the portal vein without flow. Normally measures <4mm, increases by 1mm per decade after 40yrs.

Cellulitis

Cellulitis

"Cobblestone" appearance of soft tissue suggesting infection/edema.

Fetal Heart Rate

Fetal Heart Rate

Placing the M-Mode marker over the most visibly active portion of the fetal heart allows for measurement of the fetal heart rate.

Free Fluid

Free Fluid

Free fluid in the hepatorenal recess.

Hydronephrosis

Hydronephrosis

Severe hydronephrosis.

Thoracic Aorta Aneurysm

Thoracic Aorta Aneurysm

Subxiphoid view of thoracic aorta, markedly dilated (>3cm) with thrombus.

Pericardial Effusion

Pericardial Effusion

Mild pericardial effusion in a patient with pleuritic chest pain.

Inferior Vena Cava

Inferior Vena Cava

IVC without significant respiratory variation.

B-lines

B-lines

B-lines extending deep from pleura suggestive of interstitial fluid accumulation (pulmonary edema).

"Shred" sign

"Shred" sign

Irregular, "shredded" pleural line suggestive of consolidation.

Pneumothorax

Pneumothorax

Transition point with loss of lung sliding in a patient with a small spontaneous pneumothorax.

Volvulus


Swirling mesenteric vessels in mid-pelvis associated with narrowed segments of small bowel and fluid-filled proximal small bowel raises concern for volvulus and small bowel obstruction.

Head Trauma (Radiographic Evolution)

CT Head (Initial)

CT Head (Initial)

- Noncontrast axial images through the head demonstrate no evidence of skull fracture.
- Large lentiform-shaped mixed density extra-axial acute epidural hematoma in the right parietal occipital
- Associated subdural hematoma tracking along right convexity toward the right temporal lobe.
- There is no evidence of midline shift.

CT Head (+8h)

CT Head (+8h)

- Significant interval increase in the size of the right hemispheric subdural hematoma
- There is now midline shift from right to left at the level of the septum pellucidum measuring 10 mm, partial effacement of the right lateral ventricle and subfalcial herniation.
- Scattered subarachnoid blood is redemonstrated.
- Comminuted fractures of the nasal bone are present and there is overlying and associated periorbital soft tissue swelling.

CT Head (+16h, s/p SDH evacuation)

CT Head (+16h, s/p SDH evacuation)

- Interval gross total evacuation of right hemispheric subdural hematoma.
- Moderate anterior bifrontal subdural and right epidural air is present.
- Small scattered subarachnoid and intraventricular blood is redemonstrated.

Elevated Hemidiaphragm

CXR - PA
CXR - Lateral

Causes of an Elevated Hemidiaphragm

Causes of an elevated hemidiaphragm

References:

  1. Lavender, JP, Potts DG (1959). Differential diagnosis of elevated right diaphragmatic dome. The British journal of radiology, 32(373), 56–60.
  2. Nason, L. K., Walker, C. M., McNeeley, M. F., Burivong, W., Fligner, C. L., & Godwin, J. D. (2012). Imaging of the diaphragm: anatomy and function. Radiographics : a review publication of the Radiological Society of North America, 32(2), E51–70. doi:10.1148/rg.322115127
  3. Prokesch, R. W., Schima, W., & Herold, C. J. (1999). Transient elevation of the hemidiaphragm. The British journal of radiology, 72(859), 723–724.
  4. Burgener, F., Kormano, M. & Pudas, T. (2008). Differential diagnosis in conventional radiology. Stuttgart New York: Thieme.