Differential Diagnosis for Lower Right Side Abdominal Pain

Given the symptoms of lower right side abdominal pain, recent menstrual period, negative pregnancy test, clear urine dip, and a history of appendectomy, the following differential diagnoses can be considered:

• Single Most Likely Diagnosis

  • Ovarian Cyst: The patient's recent menstrual period and negative pregnancy test, combined with the location of the pain, suggest that an ovarian cyst could be the cause. Ovarian cysts are common in women of reproductive age and can cause lower abdominal pain.

• Other Likely Diagnoses

  • Constipation or Bowel Obstruction: Although the urine dip is clear, constipation or a partial bowel obstruction could cause lower abdominal pain. The history of appendectomy might increase the risk of adhesions leading to bowel obstruction.
  • Diverticulitis: Inflammation of a diverticulum in the colon can cause lower abdominal pain, especially if the diverticula are located in the sigmoid colon, which is on the left but can refer pain to the right side in some cases.
  • Ectopic Ovarian Tissue or Residual Ovarian Tissue: If the patient has a history of ovarian surgery, there's a possibility of ectopic ovarian tissue or residual ovarian tissue causing pain.

• Do Not Miss Diagnoses

  • Ectopic Pregnancy: Despite the negative pregnancy test, ectopic pregnancies can present with abdominal pain and a negative urine pregnancy test early in the pregnancy. It's crucial to consider this diagnosis due to its high morbidity and mortality if missed.
  • Intestinal Ischemia: This condition involves insufficient blood flow to the intestines and can cause severe abdominal pain. It's less common but critical to diagnose early to prevent severe complications.
  • Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic abdominal pain and may not be immediately suspected without further diagnostic testing.

• Rare Diagnoses

  • Endometriosis: While not the most likely cause of acute pain, endometriosis can cause chronic pelvic pain and could be considered if other diagnoses are ruled out.
  • Ruptured Corpus Luteum Cyst: Similar to an ovarian cyst but specifically related to the corpus luteum, this could cause acute abdominal pain.
  • Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery can mimic appendicitis and cause lower abdominal pain, though it's less common.

Each of these diagnoses should be considered in the context of the patient's full medical history, physical examination, and further diagnostic testing as necessary.