Introduction

Allergic Bronchopulmonary Aspergillosis (ABPA) is a complex hypersensitivity response to the common fungus Aspergillus fumigatus, typically occurring in patients suffering from chronic bronchial asthma or cystic fibrosis. The disease presents with a wide variety of radiological manifestations. The characte-ristic high-resolution computed tomography (HRCT) findings of ABPA include central bronchiectasis, mucoid impaction, high-attenuation mucus, linear or branching centrilobular opacities ("tree-in-bud" pattern), atelectasis, peripheral consolidation, diffuse ground-glass opacities, mosaic perfusion, and air trapping on expiratory imaging(1).

While the differential diagnosis for central bronchiectasis is vast and frequently inconclusive, the specific radiological finding of hyperdense mucus serves as a highly characteristic, virtually pathognomonic feature of ABPA that significantly aids in clinching the clinical diagnosis.

Case Report

A 52-year-old female with a 10-year history of poorly controlled bronchial asthma presented to the outpatient department with a 3-week history of worsening cough, low-grade fever, and thick, yellowish expectoration containing brownish plugs. On clinical examination, bilateral coarse wheezing and rhonchi were audible, predominantly over the upper lung fields.

Initial laboratory evaluations revealed a significantly raised total leukocyte count with profound peripheral blood eosinophilia (absolute eosinophil count: 1,250 cells/µL). Total serum immunoglobulin E (IgE) levels were markedly elevated at 8,400 IU/mL (normal < 100 IU/mL).

The baseline posteroanterior chest radiograph dem-onstrated bilateral central bronchiectasis associated with a dense, branching, radio-opaque mass-like shadow in right upper lobe, mimicking a central pulmonary lesion (Fig. 1). To further characterize this finding, an unenhanced thoracic CT exam was performed. The HRCT revealed bilateral central bronchiectasis (Fig. 3) associated with hyperdense branching mucus plugging within bronchus of right upper lobe (Fig. 2). The impacted mucoid material demonstrated a distinctly high attenuation value of 101 Hounsfield Units (HU), making it denser than adjacent paraspinal skeletal muscle (Fig. 2).

Figure 3: Unenhanced axial lung-window CT image demonstrating widespread, classic central bronchiectasis.

IMAGING FINDINGS & DISCUSSION

Hyperdense or High Attenuation Mucus (HAM) plugs remain a crucial diagnostic cornerstone in evaluating ABPA. Radiologically, HAM is defined as mucoid impaction within dilated bronchi that exhibits an attenuation value greater than normal paraspinal skeletal muscle on non-contrast HRCT(2-4). This distinct hyperdensity occurs in approximately 30% of patients diagnosed with ABPA. The physical mechanism underlying this high density is attributed to the condensation of calcium salts and the accumulation of metallic ions (such as iron & manganese) manufactured by proliferating fungal hyphae within the stagnant mucus.

From a clinical standpoint, the presence of the HAM sign carries important prognostic implications. It has been postulated that the presence of dense mucoid impaction directly correlates with increased severity of ABPA. Patients presenting with the HAM sign have been reported to exhibit higher baseline mean eosinophil counts, higher mean serum IgE levels, and elevated Aspergillus fumigatus-specific IgE levels. Furthermore, these patients demonstrate a significantly greater likelihood of experiencing clinical and radiological relapses following the cessation of standard therapy(3,5,6,7).

CLINICO-RADIOLOGICAL OVERVIEW

HRCT plays a pivotal role in establishing a clear diagnosis of ABPA, particularly in identifying proximal airway abnormalities when conventional chest radiographs show non-specific findings or simulate neoplastic masses.

SOURCE OF FUNDING

The Authors received no financial support for the research, authorship, or publication of this article.

References