Abstract | November 6, 2020
Solitary Pulmonary Nodule – An Unusual Presentation
Learning Objectives
- Discuss the types and associated conditions of extramedullary hematopoiesis.
- Discuss the pathophysiology of extramedullary hematopoiesis.
- Describe an uncommon presentation of extramedullary hematopoiesis in a patient diagnosed with a solitary pulmonary nodule.
Introduction: We are presenting a case of a unique pathological finding in a patient diagnosed with a solitary pulmonary nodule.
Case: 75 YO white male, with a past medical history of COPD, OSA, and HFpEF presented to the pulmonology clinic for a follow-up visit. No complaint of any cough, dyspnea, hemoptysis, fever, chills, or any recent weight change was reported. The patient has a history of falls resulting in multiple rib fractures that is evident from CT scan images (figure 6). Physical examination was negative for hepatosplenomegaly and otherwise unremarkable. Labs including CBC, serum electrolytes, and peripheral smear were clear of any acute findings as well. Chest X-ray (CXR) performed recently showed a left-sided pleural effusion and increased interstitial markings followed by a CT chest w/o contrast that was positive for an incidental 7.7 mm nodule within the left lower lobe without any calcifications. This was followed up with a PET CT that was negative for any malignant tissue, and follow up CT, recommended in 6 months, reported a slight increase in size to 10 x 9.3 mm.
An ultrasound-guided surgical lung biopsy reported ALVEOLATED LUNG PARENCHYMA WITH TRILINEAGE HEMATOPOIESIS. Figure 3 shows a microscopic appearance of the biopsied specimen. To the right, normal lung parenchyma is visible with type 1 and 2 pneumocytes. Trilineage hematopoietic cells are visible on the left. Figure 4 is a magnified version also depicting the trilineage cytology with megakaryocytes, immature red cells, and white cells, surrounded by fat cells. This was followed by a bone marrow biopsy that was reported normal. Our patient was followed in the pulmonology clinic for the next five years and remains asymptomatic to date.
Discussion: The development and proliferation of hematopoietic tissue outside of the BM territory is defined as extramedullary hematopoiesis (EMH). It is a normal phenomenon during fetal development and immune responses (active EMH) but is also seen as a compensatory mechanism with an inadequate BM functioning (passive EMH) seen with various hematologic pathologies, including chronic myeloproliferative disorders (primary myelofibrosis), hemoglobinopathies (thalassemia or sickle cell anemia), and secondary to bone marrow radiation. Liver, spleen, and lymph nodes are commonly involved sites, but the kidney, adrenal gland, lung, etc. can be involved as well.
Our case is a unique presentation of trilineage EMH in a patient without any history of myeloproliferative neoplasia that was evident from a negative bone marrow biopsy. Intra-pulmonary involvement is rare, and the pathogenesis of pulmonary EMH is unclear and poorly understood. Embryonic hematopoietic stem cell, progenitor cell mobilization, and decreased splenic capacity to filter blood is the mechanism of EMH in primary myelofibrosis. Due to the history of left-sided 4th rib fracture and the proximity of the nodule to the fracture site (figure 5 and 6), we hypothesize that the bone marrow-derived hematopoietic cells may have implanted in the pleural space and contributed to its development. The rib fracture and nodule can be visualized in figures 5 and 6.
