Epidermoid cyst; Increased 18F-fluorodeoxyglucose (FDG) metabolic activity in the soft tissues of the bilateral upper thighs (False positive findings); lytic skull lesion/non-FDG avid lytic lesion in the left frontal skull with a small soft tissue component.; This case was reported in a literature article and described the occurrence of epidermoid cyst in a 7-month-old female patient who received DTPa-HBV-IPV (DTPa-HBV-IPV) for prophylaxis. (A unique case of increased 18f-FDG metabolic activity in the soft tissues of the bilateral upper thighs due to immunizations in a pediatric patient)   Co-suspect products included Hib UNK (Hib vaccine) for prophylaxis and PNEUMOCOCCAL 13 VALENT CONJUGATE VACCINE (PCV VACCINE) for prophylaxis.   On an unknown date, the patient received DTPa-HBV-IPV (intramuscular), Hib vaccine (intramuscular) and PCV VACCINE (intramuscular). On an unknown date, less than 2 months after receiving DTPa-HBV-IPV and Hib vaccine, the patient experienced epidermoid cyst (serious criteria GSK medically significant), metabolic disorder and osteolytic lesion. On an unknown date, the outcome of the epidermoid cyst, metabolic disorder and osteolytic lesion were unknown.   It was unknown if the reporter considered the epidermoid cyst and osteolytic lesion to be related to DTPa-HBV-IPV and Hib vaccine. The reporter considered the metabolic disorder to be related to DTPa-HBV-IPV and Hib vaccine.  Additional details were provided as follows: This case was reported in a literature article and described the occurrence of increased 18F-fluorodeoxyglucose (FDG) metabolic activity in the soft tissues of the bilateral upper thighs(False positive findings) in a 7-month-old female patient, who was vaccinated with unspecified diphtheria-tetanus-pertussis with hepatitis B and inactivated polio virus (DTaP-HepB-IPV) vaccine and unspecified Haemophilus influenzae type b (Hib) vaccine (manufacturer unknown for both) for prophylaxis.  The patient was a female. At 4 months of age, approximately 114 days before the positron emission tomography/computed tomography (PET/CT), the patient received  unspecified diphtheria-tetanus-pertussis with hepatitis B and inactivated polio virus (DTaP-HepB-IPV) vaccine intramuscularly in the right thigh along with unspecified Haemophilus influenzae type b (Hib) vaccine and unspecified pneumococcal conjugate (PCV) vaccine intramuscularly in the left thigh (batch number not provided for all vaccines). No information on patient's medical or family history or concurrent condition or concomitant medication was provided.  On an unspecified date, approximately 51 days before the PET/CT, the patient received  unspecified diphtheria-tetanus-pertussis with hepatitis B and inactivated polio virus (DTaP-HepB-IPV) vaccine intramuscularly in the right thigh along with unspecified Haemophilus influenzae type b (Hib) vaccine and unspecified pneumococcal conjugate (PCV) vaccine intramuscularly in the left thigh (administration site not reported; batch number not provided for all vaccines) at 6 months of age.   On an unspecified date, an unknown time after vaccination, the patient with a lytic skull lesion who was referred for initial staging 18F-fluorodeoxyglucose (FDG) Positron emission tomography/computed tomography (PET/CT) for presumed Langerhans cell histiocytosis or possible neoplastic process was presented.  Approximately 51 days after vaccination, the patient underwent noncontrast enhanced CT of the head, which demonstrated a non-FDG avid lytic lesion in the left frontal skull with a small soft tissue component. (The lytic frontal skull lesion did not have FDG avidity). However, multiple PET avid nodules in the soft tissues of the bilateral anterior thighs were present. Whole body maximum intensity projection (MIP) showed expected physiologic uptake, as well as abnormal focal areas of increased metabolic activity in the bilateral thighs. Imaging was performed approximately 99 min after the radiotracer injection. Axial 18F-FDG PET/CT images display coregistration of abnormal focal hypermetabolic foci within soft tissues of the anterior thighs bilaterally. No activity was evident within the inguinal lymph nodes. At the time of injection, the patient weighed 5.7 kg and had a blood sugar of 57 mg/dL. Skull biopsy eventually characterized the skull lesion as an epidermoid cyst. Treatment was unknown. Outcome was not reported. The authors commented, "Increased FDG metabolic activity at sites of vaccination has previously been demonstrated. Both the intramuscular sites of vaccine injection and local lymph nodes can demonstrate increased FDG uptake. This can lead to regions of false positive metabolic activity, when evaluating for other systemic inflammatory or neoplastic processes on PET.  A singular case report describes similar activity in one thigh of an infant who received vaccination 5 days prior to the 18F-FDG PET/CT.1 However, such activity has not been seen in the bilateral thighs nor in an infant who received vaccinations over 50 days prior to the scan, thus invoking the question as to how long such activity can last following immunizations in infants. This also again emphasizes the importance of acquiring the vaccination history in infants and children to avoid attributing these false positive findings as pathologic activity This article is not available for regulatory submission due to copyright restriction