Histopathology of Pneumothorax: Potential Diagnostic Pitfalls

To the Editor.—This letter calls attention to 3 potentially significant pitfalls that may result from misinterpretation of vascular alterations in the lung and pleural tissues in patients with pneumothorax. Two of the 3 vascular alterations (pseudoeosinophilic vasculitis and pseudohypertensive arteriopathy) have previously been published but may nonetheless be underrecognized. The third, a peculiar pseudo arteriovenous malformation (AVM), does not appear to have been previously reported.A woman, 44 years old, presented with sudden onset of pleuritic pain and shortness of breath. Clinicoradiologic evaluation supported a diagnosis of pneumothorax. At surgery, bullae from the left upper lobe were excised and submitted for histopathologic evaluation. In addition to pleural fibrosis, bullae formation, and chronic inflammation, the most prominent microscopic finding was a florid, eosinophil-rich, nonnecrotizing transmural vasculitis involving medium-sized arteries (Figure 1). The differential diagnosis included Churg-Strauss syndrome, Langerhans cell histiocytosis, eosinophilic vasculitis such as seen in systemic lupus erythematosus, and a parasitic infestation of the lung. A workup including immunostains for S100 protein and CD1a combined with a clinicoradiographic evaluation of the patient helped to exclude all of the previously mentioned diagnoses. The correct diagnosis was reactive eosinophilic vascular infiltration (REVI). First described by Luna et al,1 REVI is characterized by a rather impressive (at least in this particular case) eosinophilic infiltration of vascular walls, without necrosis, mimicking some of the previously cited conditions. In contrast to true vasculitis, REVI is limited to and more pronounced in the immediate subpleural regions and fades toward the interior of the lung. REVI has received limited attention in current major textbooks of pulmonary pathology. It is briefly noted in one text2 but not mentioned in others.3–8 Its true frequency is not known. Among 29 cases of spontaneous pneumothorax seen at our institution since January 2004, 5 had mild perivascular eosinophilia but none showed the extreme degree of vascular eosinophilic inflammation noted in the index case. The pathogenesis of REVI is unknown. A defect related to vascular transport of eosinophils to the injured pleural surface has been considered.1 Awareness and recognition of REVI may lessen patient anxiety and limit unnecessary clinical and serologic investigations into possible vasculitis syndromes. The 2 patients reported by Luna et al were without symptoms up to 48 months from diagnosis suggesting a favorable outcome.An adolescent boy, 17 years old, presented with acute symptomatology related to recurrent pneumothorax. Starting at age 12 the patient, who has a tall, slender body habitus, had experienced several painful bouts of pneumothorax. At surgery, fibrotic tissue from the apex of his right lung was removed. Microscopic examination showed chronic pleuritis with fibrosis and single thick-walled vessels in the pulmonary parenchyma (Figure 2) as well as conglomerates of equally thick-walled vessels beneath the pleural surface (Figure 3). The vascular changes affecting single parenchymal vessels closely resembled pulmonary hypertension. This type of vasculopathy affecting single vessels is well described in some texts of pulmonary pathology36 but not in others.24578 Cyr and associates9 reviewed 20 cases of idiopathic spontaneous pneumothorax and determined the prevalence and severity of pseudohypertensive medial and intimal lesions in pulmonary arteries and veins. Pulmonary artery medial hypertrophy, venous intimal fibrosis, and pulmonary artery intimal fibrosis were found 15%, 80%, and 90% of the cases, respectively. The authors concluded this rather common but underrecognized vasculopathy is possibly secondary to chronic inflammation and fibrosis and of no clinical or hemodynamic significance and should not be confused as evidence of pulmonary hypertension. Our findings in the previously cited 29 patients, showing medial hypertrophy and intimal thickening in 13 of the 29 cases, confirm the high frequency of these pseudohypertensive changes.The Cyr paper, however, and none of the previously cited texts of pulmonary pathology address the occurrence of thick-walled vascular conglomerations in cases of pneumothorax such as those illustrated in Figure 3. At first, these changes prompted the initial consideration of an acquired AVM and the possibility of a right to left shunt. However, in genuine AVMs, the affected vasculature adopts an ectatic or cavernous appearance and the vascular walls become thin and stretched (Figure 4). In all probability, the pseudo AVM changes are likely to represent a proliferative vasculopathy secondary to rupture and/or inflammation of blebs/bullae with subsequent formation of adhesions and the development of “parasitic” hypertrophied vessels within the adhesions. Similar vascular proliferations may be seen in tissues harboring old healed abscesses and other chronic inflammatory conditions of the lung. In the setting of pneumothorax, pseudo AVM changes appear to be rare, having been found in the index patient but none of the other 29 cases. As is the case with REVI and the pseudohypertensive changes, these vascular lesions will assume unwarranted clinical importance only if surgical pathologists misinterpret their significance.I acknowledge the helpful review of case 2 by John C. English, MD, University of British Columbia, Vancouver.

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