AJR 2004; 183:99-101
© American Roentgen Ray Society
Placental Transmogrification of the Lung: CT–Pathologic Correlation of a Rare Pulmonary Nodule
G. R. Ferretti1,
M. Kocier1,
D. Moro-Sibilot2,
P. Y. Brichon3 and
S. Lantuejoul4
1 Service de Radiologie et Imagerie Médicale, CHU Grenoble, BP 217,
Grenoble 38043, CEDEX 9, France.
2 Département de Médecine Aiguë Spécialisée,
CHU Grenoble, France.
3 Service de Chirurgie Thoracique, CHU Grenoble, France.
4 Service de Pathologie Cellulaire, CHU Grenoble, France.
Received August 11, 2003;
accepted after revision November 10, 2003.
Address correspondence to G. R. Ferretti
(gferretti{at}chu-grenoble.fr).
Introduction
Pulmonary placental transmogrification is an unusual locally destructive
lesion in the lung related to emphysematous bulla occurring in young patients
[1]. Histologically, placental
transmogrification has a specific presentation characterized by the formation
of placental villuslike papillary structures
[2]. The core of the papillae
contain proliferating vessels, inflammatory cells, and fat
[1,
2]. We report one case of
placental transmogrification of the lung discovered incidentally on a chest
radiograph. We emphasize the high-resolution CT findings correlated with the
pathology of this unusual tumor of the lung.
Case Report
A 40-year-old asymptomatic man who had smoked 20 cigarettes per day for 12
years presented for routine chest radiography. Radiograph showed a 25-mm
nodule in the left lower lobe. MDCT (VolumeZoom, Siemens) performed without
contrast medium injection using 1-mm sections, 120 kVp, and 80 mA confirmed
the solitary nature of the nodule and did not show any emphysematous lesions
in the lung parenchyma. The nodule was located subpleurally in the posterior
segment of the left lower lobe. High-resolution CT showed unusual features.
The nodule was well demarcated by a thin wall; had sharp and smooth contours;
and contained a mixture of air, soft tissue, and fat (–60 H) in lobules
(Fig. 1A,
1B,
1C,
1D). No calcification was
present. Because the internal structure of the nodule was not suggestive of a
typical lipoma or a hamartoma, surgical resection of the nodule was
performed.
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Fig. 1A. —40-year-old asymptomatic man with well-defined subpleural
nodule in left lower lobe. High-resolution CT scan obtained using lung window
settings shows upper part of nodule is limited by thin wall (arrow)
and contains air.
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Fig. 1B. —40-year-old asymptomatic man with well-defined subpleural
nodule in left lower lobe. High-resolution CT scan obtained using mediastinal
window settings shows that central part of nodule combines air and soft-tissue
densities.
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Fig. 1C. —40-year-old asymptomatic man with well-defined subpleural
nodule in left lower lobe. High-resolution CT scan obtained using lung window
settings shows that central part of nodule contains soft-tissue and fat-tissue
(–60 H) attenuating components.
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Fig. 1D. —40-year-old asymptomatic man with well-defined subpleural
nodule in left lower lobe. Histomicrograph shows microscopic features of
placental transmogrification. Lesion abuts visceral pleura and is composed of
villuslike structures admixed with remnants of alveolar walls, with core of
structures being filled by mature adipose tissue. (H and E, and saffron,
x100)
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Macroscopically, the wedge resection contained a subpleural lesion composed
of gelatinous and papillary fatty projections that were several millimeters in
diameter. No mucus or blood filled this mixed cystic and solid lesion that
appeared well demarcated from the normal surrounding lung parenchyma.
Histologically, the lesion consisted of placental or villuslike structures
surrounded by hyperinflated air spaces
(Fig. 1D). At higher
magnification, these villuslike structures corresponded to alveolar walls
enlarged by mature adipose tissue and fibroblasts intermixed with thin or
dilated capillaries. No smooth-muscle, cartilage, bronchial structures, or
mesenchymal or inflammatory cells were present in these papillary structures.
These papillary structures were lined either by flattened type I alveolar
cells or by hyperplastic type II pneumonocytes. Lipoblasts and atypical
epithelial cells were absent. The overlying pleura was normal, and the
adjacent lung, which was free of emphysematous changes, was also normal. The
final diagnosis was placental transmogrification of the lung.
Discussion
Pulmonary placental transmogrification is a benign lesion that was first
described in 1979 [3].
Histologically, pulmonary placental transmogrification resembles immature
placental structures, but the tissues do not bear any biologic properties of
the placenta [2]. To date,
fewer than 15 cases have been reported in the literature. Clinically,
pulmonary placental transmogrification may be asymptomatic, as in our patient,
or may be associated with chronic obstructive lung disease, pneumothorax,
bronchopneumonia, or respiratory distress
[1]. The origin and
pathogenesis remain unknown. Pulmonary placental transmogrification is thought
to be a reactive lesion secondary to emphysema, but a congenital origin has
not been excluded [2]. It is
usually described in association with bullous emphysema
[1–3],
and the prognosis after surgical resection is excellent
[2].
The high-resolution CT appearance of the nodule in our patient was
surprising in that it contained air, fat, and soft-tissue attenuating
components in a well-defined nodular structure. To our knowledge, this report
is the first for high-resolution CT features of placental transmogrification
of the lung presenting as a pulmonary nodule. The radiologic differential
diagnostic of this lesion should include lesions with fatty components and
lesions containing air. Fatty tumors of the lung are rare. Fat is present in
lipomas and hamartomas [4]. CT
shows fat as low-density material (–40 to –120 H), and MRI shows
fat as high signal intensity on T1-weighted images and intermediate signal
intensity on T2-weighted images. Fat is the only component of lipomas, which
appear as well-circumscribed nodules in the periphery of the lung surrounded
by normal lung tissue [5]. They
represent approximately 0.1% of all pulmonary tumors.
Hamartomas represent the most common benign pulmonary neoplasm of the lung,
accounting for approximately 6% of all pulmonary nodules. Its prevalence at
autopsy reaches 0.25% [6].
Pulmonary hamartomas consist of a mixture of cartilage, connective tissue,
smooth muscle, marrow, bone, and variable amounts of fat. On CT, hamartomas
are typically spherical lobulated nodules with well-defined margins surrounded
by normal lung tissue. Fat is detected in approximately 50% of hamartomas, and
its presence is considered a reliable indicator of hamartoma, precluding a
transthoracic biopsy or surgical resection
[6]. On CT, air bronchogram in
a hamartoma has been reported in one of 30 cases and corresponds
pathologically to bronchial epithelium in cartilaginous tissue
[7].
The presence of air in a nodule may result from cavitation that can occur
in both benign and malignant nodules. Benign cavitary nodules usually have
smooth thin walls (< 4 mm), as in our patient, whereas malignant nodules
typically have irregular thick walls (> 16 mm)
[8]. A significant overlap
exists, making wall thickness alone an inaccurate feature for differentiating
malignant from benign cavitary nodules.
In summary, we reported the high-resolution CT findings of pulmonary
placental transmogrification, an unusual lung tumor that contains air, fat,
and soft-tissue. This tumor should be included in the differential diagnosis
of benign lung tumors with fatty and air components.
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Introduction
Case Report
