DOI:10.2214/AJR.05.0354
AJR 2006; 187:149-152
© American Roentgen Ray Society
16-MDCT and MR Angiography of Accessory Diaphragm
Alberto Hidalgo1,
Tomás Franquet1 and
Ana Giménez1
1 All authors: Department of Radiology, Hospital de Sant Pau, Universidad
Autónoma de Barcelona, S. Antoni M Cret 167, 08025 Barcelona,
Spain.
Received March 1, 2005;
accepted after revision April 22, 2005.
Address correspondence to A. Hildago
(jhidalgop{at}hsp.santpau.es).
Keywords: chest • MDCT • MR angiography
Introduction
We describe an unusual accessory diaphragm, also known as diaphragmatic
duplication, identified on chest radiography, contrast-enhanced MDCT, and MR
angiography (MRA). In this case, the malformation was associated with a
unilateral single pulmonary vein. There are few reported cases of this rare
pulmonary malformation, which is sometimes confused with lobar atelectasis and
residual changes secondary to pulmonary infections. However, the specific
radiologic findings allow a correct diagnosis.
Case Report
A 56-year-old woman was admitted to the department of radiology for staging
of lympho-proliferative syndrome. The chest radiograph showed a linear opacity
on the right hemithorax parallel to the major fissure (Figs.
1A and
1B). Beginning at the upper
part of the right hilum, a tortuous tubular structure was also seen. When
questioned, the patient stated that some years before she had a chest
radiograph to check for a respiratory infection and that no consolidation had
been found. However, characteristics resembling posttuberculosis changes in
the right lung were seen, although she did not recall having had
tuberculosis.
An MDCT was performed with a scanner using 2.5-mm slice thickness
reconstructed at 1-mm intervals with contrast materials (Omnipaque 300
[iohexol], Amersham Health) injected at a rate of 2.5 mL/s. The thoracic CT
showed an anomalous single pulmonary right vein draining into the right upper
and middle lobes. The left superior and inferior pulmonary veins were healthy.
No anomalous arterial supply was seen. The bronchial anatomy was anomalous and
there was no bronchus intermedius. A right-middle-lobe hypoplasia and
incomplete major fissure were identified. A fine structure, which crossed
diagonally through the right lung with a hiatus in its center, was also
identified. The pulmonary vessels and bronchial tree followed an anomalous
path: they converged at the hiatus and then dispersed (Figs.
1C,
1D,
1E, and
1F).
View larger version (109K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1C —56-year-old woman with accessory diaphragm.
Maximum-intensity-projection (MIP) reconstructions on axillary, coronal, and
sagittal planes show accessory diaphragm (arrows) and anomalous path
of pulmonary vessels converging at hiatus and then dispersing.
|
|
View larger version (149K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1D —56-year-old woman with accessory diaphragm.
Maximum-intensity-projection (MIP) reconstructions on axillary, coronal, and
sagittal planes show accessory diaphragm (arrows) and anomalous path
of pulmonary vessels converging at hiatus and then dispersing.
|
|
View larger version (103K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1E —56-year-old woman with accessory diaphragm. Volume-rendered
image shows accessory diaphragm (black arrows) and anomalous course
of tracheobronchial tree converging at hiatus (white arrows) and then
dispersing.
|
|
The complex anatomy of the accessory diaphragm and anomalous pulmonary
single vein was better visualized in volume-rendered images, which clearly
showed the course of the anomalous diaphragmatic membrane and the anomalous
vein draining into the atrium.
An MRA was also performed to study pulmonary vessels
(Fig. 1G) because MRAs can
better distinguish between the arterial and venous phases. A 3D MRA (3D
interpolated, spoiled gradient-recalled echo) sequence (TR/TE,
3.8-5.0/1.3-2.0; flip angle, 12-50° [mean 27°]; number of
acquisitions, 1; mean acquisition time, 20 seconds [range, 9-28 seconds];
number of measurements, 2 or 3; partitions, 40-112 [mean, 68]; effective
thickness, 0.9-2.8 mm [mean, 1.9 mm]; matrix, 90-126 x 256 pixels) was
then performed using IV gado-pentetate dimeglumine (Magnevist, Berlex). The
dose of contrast material was 0.2 mmol/kg. The contrast material was
administered through a peripheral IV line using a hand injection technique
(1-2 mL/s).
View larger version (81K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1G —56-year-old woman with accessory diaphragm. MR angiography
image shows anomalous course of vessels. They converge at level of central
hole of accessory diaphragm (thin arrows) and then disperse.
Anomalous unilateral single pulmonary vein is also seen (thick
arrows).
|
|
Discussion
The accessory diaphragm, also known as diaphragmatic duplication, is a very
rare congenital anomaly. Usually it is not isolated and is considered part of
the lobar agenesis-aplasia complex
[1]. The accessory diaphragm
was described by Drake and Lynch in 1950
[2]. These authors thought that
the anomaly originated during the first phases of embryonic development when
the septum transversum, which originates in the diaphragm, is in an upper
position. If for some reason the septum transversum stops during its lower
migration, part of the primitive lung can be trapped by it. The septum
transversum should be kept anchored to the posterior portion of the thoracic
wall producing an additional diaphragmatic leaf. Other authors
[3] think that the accessory
diaphragm is a consequence of early bronchial tree development, which does not
allow a correct septum transversum migration.
In gross pathology, the accessory diaphragm is a fine fibromuscular
membrane with a serosal lining that is united to the anterior part of the
diaphragm. It has a posterosuperior course and produces two compartments in
the right hemithorax, trapping part of the pulmonary parenchyma. Vessels and
bronchi that supply the trapped lung pass through the central hole of the
accessory diaphragm.
On a chest radiograph, the accessory diaphragm appears in one of two ways:
When the central hiatus is very narrow, the trapped lung is not well aerated
and it appears like a mass. When the trapped lung is aerated, as in our case,
the accessory diaphragm is seen on the chest radiograph as a density that
causes haziness of the right hemidiaphragm because of the insertion of the
accessory diaphragm within the healthy diaphragm. On the lateral chest
radiograph, the accessory diaphragm is seen as an oblique thickened line
almost parallel to the major fissure
[4,
5].
The accessory diaphragm can be confused with upper or middle lobe
atelectasis. It can also be confused with a residual lesion of either a
previous inflammatory process or a previous iatrogenic process. However, none
of these situations has an anomalous trajectory of the vessels and bronchial
structures or a crowding and draping trajectory
[6].
When the lung is aerated, CT shows the accessory diaphragm as a structure
similar to the major fissure with a hole in the center. Depending on the size
of the hiatus, it can be difficult to identify the accessory diaphragm. When
the hole is small, the trapped lung can be hypodense because of air trapping.
It is always possible to see how vessels and bronchial structures converge
when they go to the central hole and then diverge.
In our case, the accessory diaphragm was associated with an anomalous
single pulmonary vein. The patient did not have a shunt, and the vein drained
into the left atrium.
Reconstruction by volume-rendered images and reformatted maximum intensity
projections allows for a better appraisal of the fibromuscular membrane and
the central hole and their relationship to vascular and bronchial structures.
In our case, the trapped lung was healthy. MRA sequences allow a better
visualization of vessels and rule out shunt-related vascular malformations.
The anatomy is better depicted with MDCT. The only advantage of MRA over MDCT
is the ability to separate arterial from venous phases.
Symptoms vary between patients. One of the problems is determining whether
the accessory diaphragm, per se, can cause symptoms or is a consequence of the
associated pulmonary malformation. Becmeur et al.
[6] evaluated seven cases of
adults, and six were operated on because symptoms were present.
Surgical treatment should be performed when there are symptoms of dyspnea
or recurrent respiratory infections because of the presence of complex
malformations in the hypoplasic lung. If the accessory diaphragm does not
produce complications, such as pulmonary infections, treatment is not
necessary [3,
6].
Acknowledgments
We are grateful to Kristy Verenga for assistance with writing in
English.
References
- Mata JM, Castellote A. Pulmonary malformations beyond the neonatal
period. In: Lucaya J, Strife J, eds. Pediatric chest
imaging. Berlin, Germany: Springer-Verlag, 2002:93
-110
- Drake EH, Lynch JP. Bronchiectasis associated with anomaly of the
right pulmonary vein and right diaphragm. J Thorac
Surg 1950; 19:433
-437[Medline]
- Davis WS, Allen RP. Accessory diaphragm: duplication of the
diaphragm. Radiol Clin North Am 1968;6
: 253-263[Medline]
- Kenanoglu A, Tuncbilek E. Accessory diaphragm in the left side.
Pediatr Radiol 1978;7
: 172-174[Medline]
- Wille L, Holthusen W, Willich E. Accessory diaphragm: report of 6
cases and a review of the literature. Pediatr Radiol1975; 24:14
-20
- Becmeur F, Horta P, Donato L, Christmann D, Sauvage P. Accessory
diaphragm: review of 31 cases in the literature. Eur J Pediatr
Surg 1995; 5:43
-47[Medline]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
Top
Introduction
Case Report
