This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
According to WHO classification of periapical pathology, 4.81 means: 
Select and explain. 
A. Periapical cyst, B. Lateral cyst, C. Residual cyst, D. Inflammatory periodontal cyst
C: Residual cyst
Answer: C: Residual cyst 
Explanation: WHO Classification:

Ko 4.4 Acute Apical Periodontitis
Ko 4.5 Chronic Apical Periodontitis
Ko 4.6 Periapical Abscess with sinus formation
	
4.60 Sinus to maxillary antrum
4.61 Sinus to nasal floor
4.62 Sinus to oral cavity
4.63 Sinus to outer skin of face


Ko 4.7 Periapical Abscess without sinus
Ko 4.8 Periapical cyst
	
4.80 Apical / lateral cyst
4.81 Residual cyst
4.82 Inflammatory paradental cyst.