Bird’s nest sign - revisited

CASE PRESENTATION A 62-year-old diabetic male presented with a cough and fever of 4 days duration. The cough was productive of purulent sputum. Hypertension and coronary artery disease were associated. Urinalysis showed ketone bodies. Blood examination showed hemoglobin of 10.1 gms/dL and a total leucocyte count of 17,700/cu.mm with 81% polymorphonuclear leucocytes. Random plasma blood sugar was 405 mg/dL and serum creatinine was 2.71 mg/dL. Viral serology was negative. The sputum smears were negative for acid-fast bacilli and bacterial culture was sterile. Direct microscopy of potassium hydroxide (KOH) wet mount of sputum demonstrated hyaline, aseptate, broad, ribbon-like hyphae with right angle branching [Figure 1] resembling mucorales[1] but the fungal culture was negative. Computed tomography (CT) of the chest [Figure 2] showed irregular and intersecting areas of stranding and lines with cystic lucencies within ground glass opacity (GGO) surrounded by a rim of consolidation appearing like a bird’s nest (Bird’s nest sign) in the apical segment of right upper lobe and two more similar smaller lesions in the superior segment of the right lower lobe. A presumptive diagnosis of pulmonary mucormycosis (PM) with diabetic ketoacidosis was made.Figure 1: KOH wet mount preparation showing hyaline, aseptate, ribbon-like hyphae with right-angle branching. 400xFigure 2: CT of chest showing bird’s nest-like lesion in the apical segment of the right upper lobe and two similar smaller lesions in the superior segment of the lower lobeMucormycosis (MM) previously called zygomycosis is an uncommon, angio-invasive, and life-threatening fungal infection belonging to the order of mucorales affecting mostly the immunocompromised individuals. Infection is usually acquired through inhalation of sporangiospores originating from mucorales growing over decaying organic matter and soil. Diabetes mellitus is the most common risk factor of MM in Asian countries with post-tubercular state and chronic renal failure as new risk factors whereas haematologic malignancies and transplantation remain as major risk factors in Western countries.[2] Clinico-radiologic features of PM are non-specific. A thin section (<3 mm) CT scan of the chest can demonstrate GGO surrounding an area of consolidation (Halo sign) or GGO surrounded by a crescent or complete ring of consolidation (Reversed halo sign (RHS)) and both signs are suggestive of invasive fungal disease in immunocompromised persons.[3] The term bird’s nest sign was first used as an early sign of PM when RHS was associated with irregular and intersecting areas of stranding or irregular lines within GGO.[4] The RHS or atoll sign or bird’s nest sign are different terms used to describe crescent or ring-shaped consolidation bands surrounding the area of GGO.[5] RHS or bird’s nest sign may also be seen in other conditions like invasive aspergillosis, tuberculosis, sarcoidosis, bacterial pneumonia, Wagener’s granulomatosis, and pulmonary infarction.[6] Haematologic malignancy is the most common risk factor of PM and RHS, bird’s nest sign, thick-walled cavity, large consolidation or necrotizing pneumonia and multiple nodules (>1 cm size) are suggestive imaging features of PM in appropriate clinical settings.[7] The diagnosis of any invasive fungal disease like PM is considered as ‘proven’ when there is histopathologic, cytopathologic or direct microscopic examination of a specimen obtained by needle aspiration or biopsy in which hyphae are seen accompanied by evidence of tissue damage or recovery of a hyaline mold by culture of a specimen obtained by a sterile procedure from a normally sterile site and clinically or radiologically abnormal site consisting of an infectious process or amplification of fungal DNA by polymerase chain reaction (PCR) combined with DNA sequencing when molds are seen in the formalin fixed paraffin embedded tissue and ‘probable’ if there are host factors, clinical features, suggestive imaging findings (Large consolidation, RHS, thick walled cavity and multiple large nodules) and demonstration of aseptate hyphae (With or without growth of mucorales) in a sample representative of lower respiratory tract like sputum, broncho alveolar lavage, bronchial brush or aspirate indicative of a mold.[8] Intravenous liposomal amphotericin B, correction of underlying disease, and debridement of all necrotic regions whenever possible is the initial treatment of choice and oral isavuconazole or posaconazole to be continued as step-down treatment until complete response is achieved but the mortality remains higher than 50%.[9] Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.