Dr. Pepe’s Diploma Casebook 167 – Big little findings – SOLVED

Findings: PA radiograph shows a curvilinear opacity in the right middle/lower lung (A, arrows). The right lung is slightly smaller than the left and the hilum looks abnormal (A, circle). Aside from slight elevation of the right hemidiaphragm, the lateral view (B) is unremarkable.

Coronal CT shows that the curvilinear line represents a scimitar vein draining below the diaphragm (C, arrow). The right pulmonary artery describes an unusual path (D, circle) and there is abnormal branching of the right main bronchus (D, circle).

An unexpected finding is an oblique band in the lower right lung (E and F, arrows). The bronchi and RLL vessels pass through an opening in the center (E and F, circles).

Final diagnosis: hypogenetic right lung with duplicated diaphragm

The reason I’m presenting this case is to discuss duplication of the diaphragm, an uncommon congenital malformation associated with hypogenetic lung.

As you all know, hypogenetic lung is a congenital malformation characterized by absence of one or two lobes of the right lung, with abnormal lower lung venous drainage (scimitar vein) in 80% of cases. It is asymptomatic and almost always occurs on the right side. Because it is symptomless, it is usually found incidentally in adults .

Typical signs in the PA chest radiograph (Fig. 1) reflect the small size of the lung:

1. Small right hemithorax with secondary dextrocardia
2. Small right hilum
3. Anomalous vein in RLL (scimitar sign), not always present

Occasionally, hypogenetic lung occurs with minimal hypoplasia, a normal-sized right lung, and absent dextrocardia. In these patients (such as the initial one), the scimitar vein and abnormal right hilum are the clues to the diagnosis.

In my experience, these cases are the ones most commonly associated with duplicated diaphragm, an infrequent malformation resulting from an alteration of caudal migration of the embryonic diaphragm.

Anatomically it appears as a band running obliquely from the chest wall to the right hemidiaphragm (Fig. 3, drawing).

If we’re lucky, we might see it as an oblique line in PA and lateral radiographs (Fig. 4), but it is usually not visible or overlooked (Fig. 5). An additional sign is blurring of the central part of the right hemidiaphragm, where the duplication ends (Figs. 4 and 5).

My hard-learned experience tells me it is very difficult to suspect duplicated diaphragm on plain films. It is usually discovered in a CT performed to confirm a hypogenetic right lung or for other reasons.
The good news is that the CT findings are pathognomonic and consist of:

1. An oblique band with a central opening
2. RLL bronchi and vessels passing through the opening and fanning out thereafter

You may wonder why I present such a rare condition, but the answer is simple:

a) It is easily recognized because of the distinctive findings. Once recognized, advise against surgery or other invasive procedures.

b) I don’t believe it’s that rare. In my career I have seen a dozen cases, the last three in this century and at the same institution. The last, seen in 2015, is the one that headed this Diploma. Two more were seen in 2004 and 2008 (Cases 1 and 2, below).

I am due to see a new case soon. Perhaps in a COVID patient, allowing me to write a useless paper about the relationship between COVID and duplicated diaphragm 🙂

Follow Dr. Pepe’s advice:
1. Duplicated diaphragm is an infrequent malformation associated with hypogenetic right lung

2. Difficult to detect in the chest radiograph

3. Easy to diagnose in CT images by the following signs:

a) Oblique band with a central hiatus in the right lower lung

b) Central hiatus that constricts RLL bronchi and vessels