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Présentation Clinique
Patiente de 48 ans tabagique, ayant une hypothyroidie
sous Eltroxine, connue migraineuse, présente depuis deux mois une
toux et des expectorations blanchâtres avec une consolidation de
la base pulmonaire gauche persistante malgré une antibiothérapie.
Evaluée par bronchoscopie et biopsie à 2 reprises
sans évidence de malignité. Apparitions de plusieurs petits nodules
et d'images rapidement progressives pulmonaires au Scan de contrôle.
Les divers moyens non invasifs de diagnostic
n'ayant abouti, une résection segmentaire a été décidée.
Pathologie
Macroscopie
La segmentectomie ventrale du lobe supérieur
droit montre sur coupe une lobulation
du tissu pulmonaire par place accentuée, réhausse par un aspect
luisant de la tranche de section. Des zones
compactes blanchatres (droites sur les images) s'intercalent
et se fondent avec le tissu pulmonaire plus rosâtre (vers la gauche).
Microscopie
Les coupes objectivent une architecture
alvolaire conservée, et marque par un revètement épaissi s'arrètant
au niveau de certaines traves fibreuses interlobulaires. Les septa
alvolaires sont tapissées par des pneumocytes en continuité avec
un épithlium cylindrique ( x 100,
x 200, x 400 ). Ce dernier présentant un caractère sécrétoire apical, présente
des zones de transition vers un épithélium
plus cuboide, non sécrtant.
Les caractères sécrétants et non sécrétant sont
exacerbés par les colorations au PAS (x 200,
x 400) et au Bleu Alcyan (x 200,
x 400 )
Diagnostic proposé:
Adenocarcinome bronchioloalvolaire,
de type mucineux, prédominant.
Bronchioloalveolar carcinoma
(Ackerman's Surgical Path. 8th Ed.)
Bronchioloalveolar carcinoma can present in
various forms that bear an important relationship to its prognosis:
a single peripheral nodule, multiple nodules, and a diffuse pneumonic-like
infiltrate. The latter two forms may involve several lobes or even
be bilateral. Often the surgeon is not aware that the lesion is
a neoplasm. Microscopically, bronchioloalveolar carcinomas have
been divided into mucinous and nonmucinous types.
The mucinous type has a glistening appearance
on gross examination; there is usually preservation of the underlying
lung architecture, with occasional distortion of airspaces by pools
of mucus. Microscopically, the tumor is formed by well-differentiated
mucin-containing columnar cells that line respiratory spaces without
invading the stroma. The tumor nodules have a topographic association
with bronchioles rather than bronchi. Continuity between tumor cells
lining alveoli and the epithelium of respiratory bronchioles or
alveolar ducts can be demonstrated. A sharp separation is often
found between the neoplastic and the normal cells, a useful diagnostic
feature.
The reported cases of benign, borderline, and welldifferentiated
malignant mucinous lung tumors are probably histogenetically
related to the mucinous type of bronchioloalveolar carcinoma. The
differential diagnosis includes primary adenocarcinoma of the conventional
type and metastatic adenocarcinoma. Bennett and Sasser compared 30
cases of bronchioalveolar carcinomas with 100 cases of ordinary lung
adenocarcinoma and found frequent overlapping patterns. Other authors
have reported the presence of multiple foci of bronchioloalveolar
carcinoma in association with conventional carcinoma. The main differences
encountered between the two tumors were a higher incidence of multiplicity
and a slightly better survival rate in the patients with bronchioalveolar
carcinoma. Most authors, including ourselves, feel that the features
of bronchioloalveolar carcinoma are distinctive enough to warrant
their separation from the other subtypes of adenocarcinoma. Interestingly,
the incidence of bronchioloalveolar carcinoma seems to be on the rise.
The nonmucinous type of bronchioloalveolar
carcinoma (which comprises 60% to 75% of the cases) presents grossly
as gray-white foci of parenchymal consolidation, sometimes associated
with a central scar. Microscopically, the tumor cells are cuboidal
rather than columnar and often have a bright eosinophilic neoplasm.
The degree of nuclear atypia and nucleolar prominence is
greater than in the mucinous variety. Apical spouts may be present
as indicators of Clara cell differentiation. Hobnail cells may be
present. Cilia are exceptionally rare; their presence should suggest
the alternative possibility of a reactive condition. Eosinophilic
intranuclear inclusions, which are PAS-positive and which
are made ultrastructurally of bundles of microfilaments, are commonly
seen.
In contrast to the mucinous type, various degrees of interstitial
fibrosis and chronic inflammatory cells (some of which are S-100 protein
positive) are usually present. When the fibrosis is extensive, the
tumor is referred to as the sclerosing variant. Psammoma bodies are
found in 13% of the cases.
Ultrastructurally and immunohistochemically,
mucinous bronchioloalveolar carcinomas show differentiation toward
bronchiolar goblet cells, whereas the nonmucinous types comprise
cells with features of Clara cells and/or type 2 pneumocytes, the
former predominating.
Alpha-1-antitrypsin is a useful marker
for Clara cell differentiation, and surfactant apoprotein is a specific
marker for type 2 pneumocytes. The latter cells are identified ultrastructurally
because of lamellar inclusion bodies. Exceptionally, foci of endocrine
differentiation are detected.
The nonmucinous type of bronchioloalveolar
carcinoma is more likely to be solitary and has a better
prognosis than the mucinous type. Sputum or bronchial washing
cytology is almost invariably negative in cases that present
as single peripheral nodules but is often positive (up to
88% of the cases) for the multinodular and pneumonic-like forms.
Percutaneous fine needle aspiration has been used successfully for
the detection of this tumor.
The existence of a benign counterpart of nonmucinous
bronchioloalveolar carcinoma has been postulated, and the term papillary
adenoma has been proposed for it. Another benign tumor allegedly
composed of type 2 pneumocytes is so-called sclerosing hemangioma.
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