A 60-year-old man presents to his physician as part of his routine annual medical check-up. He has no specific complaints but mentions that he has often experienced fatigue over the past few months. His past medical history is noncontributory. On physical examination, his temperature is 37.2°C (98.8°F), pulse rate is 84/min, blood pressure is 130/86 mm Hg, and respiratory rate is 18/min. On general examination, mild pallor is present. Palpation of the abdomen reveals splenomegaly, which extends 6.35 cm (2.5 in) below the left costal margin. There is no hepatomegaly. Laboratory studies show the following values: Hemoglobin 9.7 g/dL Total leukocyte count 30,000/mm3 Granulocytes 83% Lymphocytes 10% Eosinophils 5% Basophils 1% Monocytes 1% Platelet count 700,000/mm3 The physician orders a bone marrow biopsy analysis of hematopoietic cells. The report shows the presence of a t(9;22)(q34; q11) translocation. Which of the following is the most likely diagnosis?

Transient myeloproliferative disorder

Chronic myelomonocytic leukemia

Myelodysplastic syndrome/myeloproliferative neoplasm, unclassifiable

A 9-year-old boy is brought to the physician by his parents because of right-sided shoulder pain for 1 day. He has not had chills or sweating. Over the past year, he was treated twice in the emergency department for painful swelling of his hands and feet. He emigrated with his family from Kenya 2 years ago. His temperature is 37.4°C (99.3°F), pulse is 96/min, and blood pressure is 123/82 mm Hg. Physical examination shows no tenderness, erythema, or joint swelling of the shoulder. Laboratory studies show: Hemoglobin 7 g/dL Mean corpuscular volume 88 μm Reticulocyte count 9% Leukocyte count 12,000/mm3 A peripheral blood smear is most likely to show which of the following abnormalities?

Nuclear remnants in erythrocytes

Ring-shaped inclusions in erythrocytes

Erythrocytes with no central pallor

A 66-year-old woman is brought to the emergency department because of fever, chills, night sweats, and progressive shortness of breath for 1 week. She also reports generalized fatigue and nausea. She has type 2 diabetes mellitus and hypothyroidism. Current medications include metformin, sitagliptin, and levothyroxine. She appears ill. Her temperature is 38.7°C (101.7°F), pulse is 104/min, and blood pressure is 160/90 mm Hg. Examination shows pale conjunctivae and small nontender hemorrhagic macules over her palms and soles. Crackles are heard at both lung bases. A grade 2/6 mid-diastolic murmur is heard best at the third left intercostal space and is accentuated by leaning forward. The spleen is palpated 1–2 cm below the left costal margin. Laboratory studies show: Hemoglobin 10.6 g/dL Leukocyte count 18,300/mm3 Erythrocyte sedimentation rate 48 mm/h Urine Protein 1+ Blood 2+ RBCs 20-30/hpf WBCs 0-2/hpf An echocardiography shows multiple vegetations on the aortic valve. Blood cultures grow S. gallolyticus. She is treated with ampicillin and gentamicin for 2 weeks and her symptoms resolve. A repeat echocardiography at 3 weeks shows mild aortic regurgitation with no vegetations. Which of the following is the most appropriate next step in management?

CT scan of the abdomen and pelvis

A 55-year-old man comes to the physician for a routine health visit. He feels well except for occasional left-sided abdominal discomfort and left shoulder pain. He has smoked 1 pack of cigarettes daily for 20 years. He does not drink alcohol. His pulse is 85/min and his blood pressure is 130/70 mmHg. Examination shows a soft, nontender abdomen. The spleen is palpated 5 cm below the costal margin. There is no lymphadenopathy present. The remainder of the examination shows no abnormalities. Laboratory studies show: Hemoglobin 12.2 g/dL Hematocrit 36 % Leukocyte count 34,000/mm3 Platelet count 450,000/mm3 Cytogenetic testing of his blood cells is pending. Further evaluation of this patient is most likely to show which of the following findings?

Low leukocyte alkaline phosphatase score

Elevated serum β2 microglobulin

A 3-year-old boy is brought to the physician because of a 5-day history of yellowing of his eyes and skin. He has had generalized fatigue and mild shortness of breath over the past 2 months. Examination shows pale conjunctivae and scleral jaundice. The spleen is palpated 4 cm below the left costal margin. Laboratory studies show a hemoglobin concentration of 8.5 g/dL and a mean corpuscular volume of 76 μm3. A peripheral blood smear shows round erythrocytes that lack central pallor. Which of the following is the most likely cause of the splenomegaly seen in this child?

Reticuloendothelial hyperplasia

A 62-year-old man comes to the physician because of easy bruising and recurrent nosebleeds over the past 4 months. During the same time period, the patient has felt weak and has had a 10-kg (22-lb) weight loss. Physical examination shows mucosal pallor and bruising on the upper and lower extremities in various stages of healing. The spleen is palpated 4 cm below the left costal margin. Laboratory studies show anemia and thrombocytopenia. A photomicrograph of a peripheral blood smear is shown. Histologic examination of a bone marrow biopsy in this patient is most likely to show which of the following findings?

Neoplastic lymphocytes that stain positive for tartrate-resistant acid phosphatase

Neoplastic granulocytes with low leukocyte alkaline phosphatase score

Neoplastic myeloid cells that stain positive for myeloperoxidase

Neoplastic lymphoid cells that stain positive for terminal deoxynucleotidyl transferase activity

Dysplastic erythroid cells that stain positive for iron

Splenic pathology for USMLE Step 2 CK: High-Yield Pathology Lessons

Spleen Anatomy & Function - The Body's Blood Filter

Anatomy: Located in the LUQ, the spleen is composed of two main types of tissue:
- Red Pulp: The majority of the spleen; filters blood to remove old/damaged RBCs and pathogens. Contains sinusoids and Cords of Billroth.
- White Pulp: The immune center; contains Periarteriolar Lymphoid Sheaths (PALS) rich in T-cells and follicles with B-cells.
Key Functions:
- Filtration: Removes senescent erythrocytes and circulating bacteria.
- Immunity: Site of immune response to blood-borne antigens.
- Storage: Sequesters platelets (approx. 30% of total body supply).

Spleen H&E: Red and White Pulp

⭐ Asplenic individuals are highly susceptible to overwhelming infection by encapsulated bacteria (e.g., S. pneumoniae, H. influenzae, N. meningitidis).

Splenomegaly - The Oversized Filter

Enlargement of the spleen, typically defined as a weight >500 g or a length >12 cm. It arises from an exaggerated execution of the spleen's primary functions or from pathologic infiltration.

Pathophysiology & Key Causes:

Clinical Features: Often asymptomatic. May present with LUQ pain/fullness, early satiety.
Diagnosis: Palpation (Traube's space percussion), confirmed with ultrasound.

⭐ Massive splenomegaly (spleen >1000 g or extending >8 cm below the left costal margin) is highly suggestive of a myeloproliferative neoplasm (e.g., CML, primary myelofibrosis), hairy cell leukemia, or Gaucher disease.

Splenic Lesions - Cysts, Cancers & Clots

Splenic Infarction
- Cause: Embolism (e.g., infective endocarditis), local thrombosis (e.g., sickle cell disease, myeloproliferative neoplasms).
- Morphology: Pale, wedge-shaped, subcapsular lesions. Over time, they heal into fibrotic scars.
Splenic Cysts
- True Cysts (Parasitic): Most commonly caused by Echinococcus granulosus.
- Pseudocysts: No cellular lining; account for ~80% of non-parasitic cysts. Often post-traumatic.
Splenic Neoplasms
- Benign: Hemangioma is the most common primary neoplasm of the spleen.
- Malignant: Metastases are uncommon. Most malignancies are lymphomas or leukemias.
⭐ Hairy Cell Leukemia classically causes massive splenomegaly due to infiltration of the red pulp, leading to a characteristic "beefy red" appearance.

Hyposplenism & Asplenia - Life Without a Filter

Etiology: Surgical removal (splenectomy), congenital (asplenia), or functional (e.g., sickle cell disease, celiac disease).
Pathophysiology: Impaired filtration of blood and ↓ phagocytosis of opsonized bacteria, leading to immune compromise.
Peripheral Smear Findings:
- Howell-Jolly bodies: Nuclear remnants in RBCs (pathognomonic).
- Target cells, thrombocytosis, lymphocytosis.

Howell-Jolly bodies in red blood cells (hyposplenism)

⭐ Overwhelming Post-Splenectomy Infection (OPSI): A medical emergency with high mortality. Risk is lifelong but highest <2 years post-splenectomy.

High-Risk Pathogens: Encapsulated bacteria.
- 📌 SHiN: S. pneumoniae, H. influenzae type b, N. meningitidis.
Management: Vaccinations, prophylactic antibiotics.

Splenomegaly is the most common sign, often from portal hypertension or extramedullary hematopoiesis.

Hypersplenism triad: splenomegaly, cytopenias, and resolution post-splenectomy.

Splenic infarcts are typically pale, wedge-shaped lesions, often seen in sickle cell disease.

Massive splenomegaly is a hallmark of Hairy Cell Leukemia (red pulp infiltration) and myelofibrosis.

In Hereditary Spherocytosis, splenomegaly results from work hypertrophy as the spleen removes defective RBCs.

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