An 18-year-old previously healthy woman is brought to the emergency department with 2 days of fever, headache, and lethargy. She has also had nausea and several episodes of vomiting. Her temperature is 38.9 C (102 F), blood pressure is 110/60 mm Hg, and pulse is 108/min. On physical examination, the patient is diaphoretic, delirious, and has a petechial rash on the trunk and extremities. Signs of meningeal irritation are present. CT scan of the head reveals no mass lesions. She is scheduled for a lumbar puncture for cerebrospinal fluid analysis. During this procedure, which of the following anatomical landmarks helps locate the optimal site for needle insertion?
Show Explanatory Sources
This patient with fever, headache, delirium, petechial rash, and meningismus likely has meningococcal meningitis. The diagnosis is typically confirmed with lumbar puncture and cerebrospinal fluid (CSF) analysis after neuroimaging excludes a mass lesion.
The spinal cord extends from the medulla to the inferior border of the L1 vertebra in adults (L2/L3 in neonates and infants). The conus medullaris is the tapered lower part of the spinal cord, which subsequently branches out into spinal nerves forming the cauda equina. The pia mater surrounding the spinal cord projects downward to form the filum terminale, which is a filament connecting the conus medullaris to the posterior coccyx. The dura extends below the spinal cord termination level to form a sac containing the CSF, nerve roots, and cauda equina. The dura ends at S2 and fuses with the filum terminale to connect to the coccyx.
Lumbar puncture is performed with the patient in the recumbent (preferred for accurate opening pressure measurement) or sitting position. The optimal location for needle insertion is the L3/L4 or L4/L5 space as this is well below the spinal cord termination site. The L4 vertebral body lies on a line drawn between the highest points of the iliac crests, which can be visually identified and confirmed by palpation.
(Choice A) The anterior superior iliac spine is a bony projection of the iliac bone that can be used as a landmark for surface anatomy of the abdomen. This structure serves as the attachment site for the sartorius muscle.
(Choice B) The costal margin is the lower edge of the thorax formed by the anterior ends of the 7th-10th costal cartilages.
(Choice D) The inferior angle of the scapula is formed by the medial and lateral borders of the scapula and serves as the origin of the teres major muscle. This scapular region aligns with the spinous processes of T7/T8.
(Choice E) The posterior superior iliac spine is the attachment site for the sacrotuberous and posterior sacroiliac ligaments in the iliac crest. The sacral dimples in the skin overlie the posterior superior iliac spine and correspond to the S2 vertebral level.
Educational objective:
The optimal location for needle insertion during a lumbar puncture is the L3/L4 or L4/L5 space as this is well below the spinal cord termination site (L1 in adults). The L4 vertebral body lies on a line drawn between the highest points of the iliac crests.