What is the appropriate ICD‑10 code for a hypodense lesion seen on imaging?

ICD-10 Coding for Hypodense Lesions

The appropriate ICD-10 code for a hypodense lesion depends entirely on the anatomic location and underlying etiology—there is no single universal code for "hypodense lesion" as this is a radiographic descriptor, not a diagnosis.

Understanding the Coding Framework

ICD-10-CM requires coding based on the specific diagnosis rather than imaging characteristics alone 1. A hypodense lesion on CT represents decreased attenuation compared to surrounding tissue and can indicate cysts, tumors, infarcts, abscesses, or other pathology depending on location 2, 3.

Organ-Specific Coding Approach

Liver Hypodense Lesions

The coding depends on the definitive diagnosis after appropriate workup 2:

• Simple hepatic cyst: Use codes from category Q44.6 (Cystic disease of liver) or K76.89 (Other specified diseases of liver) for acquired cysts
• Hemangioma: Code as D18.01 (Hemangioma of liver)
• Hepatocellular carcinoma: Use C22.0 (Liver cell carcinoma)
• Metastatic lesions: Code as C78.7 (Secondary malignant neoplasm of liver and intrahepatic bile duct), plus the primary site
• Liver abscess: Use K75.0 (Abscess of liver) 2

Critical caveat: Liver biopsy should be considered when diagnosis is uncertain and knowledge of the specific diagnosis would alter management 2. Imaging characteristics alone may be insufficient for definitive coding.

Renal Hypodense Lesions

Small hypodense renal lesions require differentiation between cysts and tumors 3:

• Simple renal cyst: Code as N28.1 (Cyst of kidney, acquired)
• Renal cell carcinoma: Use codes from C64.- (Malignant neoplasm of kidney, except renal pelvis)
• Renal metastases: Code as C79.0- (Secondary malignant neoplasm of kidney and renal pelvis)

Important pitfall: Thin-section CT (5-mm slices) should be used to differentiate simple cysts (which show density <30 HU) from solid tumors (which remain in soft tissue range even on thin sections) 3. Coding should reflect the definitive diagnosis after appropriate imaging protocol.

Brain Hypodense Lesions

Cerebral hypodense lesions have distinct etiologies 4:

• Cerebral infarction: Use codes from I63.- (Cerebral infarction) with appropriate fourth and fifth characters for location and laterality
• Cerebral edema: Code as G93.6 (Cerebral edema)
• Brain abscess: Use G06.0 (Intracranial abscess and granuloma)
• Brain tumor: Code based on histology (e.g., C71.- for malignant neoplasm of brain)

Critical distinction: Not all hypodense lesions on CT represent permanent infarction—some may resolve, particularly in the setting of vasospasm following subarachnoid hemorrhage 4. Follow-up imaging may be necessary before assigning a definitive infarction code.

Adrenal Hypodense Lesions

Based on imaging characteristics 2:

• Adrenal adenoma (showing intracellular fat on opposed-phase imaging): Code as **D35.0- (Benign neoplasm of adrenal gland)
• Adrenal metastases: Use C79.7- (Secondary malignant neoplasm of adrenal gland)
• Indeterminate adrenal mass: May require coding as R93.5 (Abnormal findings on diagnostic imaging of other abdominal regions) pending further workup

When Definitive Diagnosis is Unavailable

If imaging findings are truly indeterminate and no tissue diagnosis exists 2:

• Use R93.- codes for abnormal findings on diagnostic imaging:
  • R93.2 (Abnormal findings on diagnostic imaging of liver and biliary tract)
  • R93.4 (Abnormal findings on diagnostic imaging of urinary organs)
  • R93.0 (Abnormal findings on diagnostic imaging of skull and head)
  • R93.5 (Abnormal findings on diagnostic imaging of other abdominal regions)

However, this should be temporary—the ICD-10-CM framework requires pursuing definitive diagnosis through appropriate workup (biopsy, advanced imaging, clinical correlation) before final coding 1, 5.

Practical Coding Algorithm

1. Identify anatomic location of the hypodense lesion
2. Review complete imaging characteristics (size, enhancement pattern, associated findings) 2
3. Correlate with clinical context (symptoms, risk factors, laboratory findings)
4. Assign code based on definitive diagnosis when available
5. Use R93.- codes only temporarily if diagnosis remains uncertain pending further workup 1
6. Add laterality and specificity as required by ICD-10-CM conventions 5

Never code solely based on the radiographic descriptor "hypodense"—always pursue and code the underlying pathologic diagnosis 1.