Dr. Pepe’s Diploma Casebook: CASE 135 – SOLVED!

Dr. Pepe

7 years ago

Dear Friends,

Today I am showing chest radiographs of a 39-year-old man with high fever and malaise.

What do you see?

Come back on Friday to see the solution!

Click here to see the see the answer

Findings: Chest radiographs show bilateral air-space infiltrates in both upper lobes (A and B, arrows). There is widening of the right superior mediastinum (A, asterisk), displacing the right wall of the trachea. Moderate scoliosis.

Three weeks after treatment the infiltrates have healed. Widening of the upper right mediastinum persists. The clue to the diagnosis lies in in the absence of the aortic knob on the left, placing the aortic arch on the right side (C, white arrow) and simulating a mediastinal mass. Due to the scoliosis, the pulmonary arch is more evident and simulates a low-lying aortic knob (C, red arrow). Unenhanced coronal CT (D) confirms the findings (A aorta, P pulmonary artery).

Final diagnosis: right aortic arch in a patient with scoliosis and healed pneumonia

I am presenting this case to discuss the importance of negative findings. In radiology teaching we stress the importance of positive findings, such as increased opacity of the lung, pulmonary nodules, etc. However, we may fail to note absence of a structure that should be present. Recognizing this absence may be vital to reach a correct diagnosis (Fig. 1).

Fig. 1. PA radiographs of two different patients with a rib abnormality. In the first one (A) it is easy to detect the increased opacity of the right 5th rib due to Paget disease. In the other patient it is more difficult to detect the widening of the second intercostal space and the apparent absence of the proximal 3rd rib (B, circle).
The widening of the space and absence of the proximal 3rd rib (C, arrow) are better seen in the cone down view. Review of a chest radiograph taken during infancy shows congenital fusion of the 3rd and 4th ribs (D, arrow) accounting for the findings.

The value of negative findings is exemplified by the following dialogue taken from the short story “Silver Blaze” by Arthur Conan Doyle:

Gregory (Scotland Yard detective): “Is there any other point to which you would wish to draw my attention?”
Holmes: “To the curious incident of the dog in the night-time.”
Gregory: “The dog did nothing in the night-time.”
Holmes: “That was the curious incident.”

Sherlock Holmes was clever enough to detect a negative finding. The fact that the dog did not bark indicated that it knew the murderer and, based in this clue, Holmes solved the case.
We radiologists should pay special attention to similar negative findings that may help solve our cases.

Negative findings can be classified into two groups:

1. Anatomic structures that are not visible
2. Findings that should be present but are not

Today I will concentrate on the first group, leaving the second for the next Diploma

Failure to visualize a normal anatomic structure can be due to three reasons:

1. It is absent
2. It is not in its normal position
3. It is hidden

There are two causes for absent anatomic structures: congenital malformation or previous surgery.
Congenital abnormalities are not rare in adults. In some cases, a structure is missing and this fact may be overlooked, especially in routine examinations. This occurred in the following patient (Fig. 2), who had yearly check-ups for five years. The chest features were reported as unchanged until 2016, when the radiologist discovered that the left hilum was absent.

Fig. 2. Routine check-up chest radiograph in an asymptomatic 44-year-old man (A) was reported as showing chronic changes in the left lung. In further yearly check-ups, the features were reported as unchanged until 2016, when the radiologist discovered that the left hilum was missing (A and B, circles) and requested a CT.
Enhanced coronal and axial CT images show that the left pulmonary artery is absent (C and D, yellow arrows). Collateral circulation from bronchial arteries is visible (B, red arrow).
Diagnosis: congenital absence of left pulmonary artery.

Previous surgery is the most common cause of a missing anatomic structure. Detecting this finding may be important for the radiologic diagnosis, as demonstrated by the cases below (Figs. 3 and 4).

Fig. 3. 47-year-old woman with back pain. Lateral radiographs shows an ivory vertebra (B, circle). The differential diagnosis is Paget disease, metastasis, or lymphoma. The diagnosis of metastasis is evident after noting the absent left breast in the PA film (A). Sagittal CT of the spine shows several sclerotic metastases. Previous mastectomy for carcinoma.

Fig. 4. 45-year-old man with acute chest pain. PA chest radiograph shows irregularity of the left hemidiaphragm and a small peripheral nodule (A, arrow).
Enhanced coronal and axial CT show several nodules in the LLL (B and C, arrows). The diagnosis is evident after discovering the absent spleen, which suggests splenosis as the origin of the nodules. The diagnosis is confirmed with labelled erythrocytes, which show several accessory spleens (D, arrows). The patient’s spleen had been removed after a car accident.

*Image bottom right: Scintigraphy with TC 99m-labelled erythrocytes*

Sometimes, anatomic structures are not seen because they are not in their normal location. A common example is right-sided aortic arch, which can simulate a mediastinal mass unless we note that the aortic knob is absent on the left side (Fig. 5).

Fig. 5. 35-year-old woman with right aortic arch (A, arrow). A mediastinal mass can be excluded because there is no aortic knob on the left (A, asterisk). Enhanced coronal CT confirms the diagnosis of right arch with an aberrant subclavian artery (B, white arrow). The small nodule under the arch is the azygos vein (A and B, red arrows).

The same occurs with the gastric bubble, which is visible in 90% of patients. Occasionally, it is not seen because the abdominal organs are inverted and the stomach lies under the right hemidiaphragm (Fig. 6) (See Caceres’ Corner, cases 178 and case 194).

Fig. 6. 45-year-old man, asymptomatic. PA chest radiograph shows the gastric bubble under the right hemidiaphragm (A, black arrow) and a prominent azygos arch (A, red arrow). The findings are characteristic of levocardia with abdominal malrotation. Axial CT in a similar patient shows the inverted stomach (S) and liver ( L). There is polysplenia (B, circle), typical of this malformation.

Anatomic structures may not be seen because they are hidden. The best example is provided by the pulmonary hila, which hide behind the cardiac shadow when displaced downwards by lower lobe collapse (Figs. 7 and 8).