AJR 2004; 182:385-392
© American Roentgen Ray Society
Identification of Juxtaforaminal Fat Pads of the Second Division of the Trigeminal Pathway on MRI and CT
Mika Yamamoto1,2,
Hugh D. Curtin1,
Pantip Suwansa-ard1,3,
Osamu Sakai4,
Tsukasa Sano2 and
Tomohiro Okano2
1 Department of Radiology, Massachusetts Eye and Ear Infirmary, Harvard Medical
School, 243 Charles St., Boston, MA 02114.
2 Department of Radiology, Showa University, School of Dentistry, 2-1-1
Kita-Senzoku Ohta-ku, Tokyo 145-8515, Japan.
3 Present address: Department of Radiology, Phramongkutklao Hospital, 335
Rajavitee Rd., Rajatavee, Bangkok 10400, Thailand.
4 Department of Radiology, Boston Medical Center, Boston University School of
Medicine, One Medical Center Pl., Boston, MA 02118.
Received July 1, 2002;
accepted after revision June 11, 2003.
Presented at the 2001 annual meeting of the Radiological Society of North
America, Chicago, IL.
Address correspondence to M. Yamamoto.
Introduction
Perineural spread can carry malignancy beyond a planned area of surgical
resection or targeted region for radiation therapy. Detection or exclusion of
perineural spread is therefore a significant goal in the evaluation of a
patient with head and neck cancer. Imaging is the primary method for detection
of this phenomenon. The second division of the trigeminal nerve is an
important potential pathway. Tumor can reach the pterygopalatine fossa and
then extend intracranially via the foramen rotundum. Such spread can enlarge
the osseous foramen. Of equal importance is the obliteration of the fat
through which the tumor must pass as it approaches the skull base.
Obliteration of the fat in the pterygopalatine fossa is a key finding
[1–5].
Fat pads at the openings of more peripheral canals and foramina also play a
role in the evaluation of perineural spread. Our objective is to show the
location and normal appearance of these fat pads and provide examples of
obliteration of the fat by tumor. Key fat pads are located along the inferior
orbital fissure, at the proximal and distal ends of the infraorbital canal,
and in the greater palatine foramen.
The Pathway of the Second (Maxillary) Division of the Trigeminal Nerve
The trigeminal nerve serves as a major conduit for sensory information from
the face and neck and provides motor innervation to the muscles of mastication
[6,
7]. The nerve separates into
three branches after exiting Meckel's cave.
The second division, the maxillary nerve with connection to the mid face,
palate, maxillary sinus, and upper teeth, traverses the fat of the
pterygopalatine fossa after exiting the skull through the foramen rotundum
(Fig. 1). The pterygopalatine
fossa is a small cleft between the posterior wall of the maxillary sinus and
the anterior surface of the pterygoid process of the sphenoid bone. The fossa
is filled with fat. The pterygopalatine ganglion lies just below the maxillary
nerve in the pterygopalatine fossa.
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Fig. 1. —Drawing shows pathway of second (maxillary) division of
trigeminal nerve. 1 = first (ophthalmic) division, 2 = second (maxillary)
division, 3 = third (mandibular) division, FO = foramen ovale, FR = foramen
rotundum, IN = infraorbital nerve, PPG = pterygopalatine ganglion, PPF =
pterygopalatine fossa, GPN = greater palatine nerve, PPC = greater palatine
nerve entering pterygopalatine canal, IF = infraorbital foramen.
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The foramen rotundum opens into the superior part of the pterygopalatine
fossa at the point where the fossa meets the inferior orbital fissure
(Fig. 2). The inferior orbital
fissure lies between the orbital surface of the greater wing of the sphenoid
bone and the lateral edge of the floor of the orbit. From the pterygopalatine
fossa, the main trunk of the maxillary nerve passes along the inferior orbital
fissure to reach the infraorbital canal. The continuation of the nerve becomes
the infraorbital nerve carried by the infraorbital canal anteriorly along the
floor of the orbit to the anterior opening of the canal. This opening into the
soft tissues of the face is the infraorbital foramen, positioned 4–5 mm
below the inferior orbital rim. The nerve emerges from the infraorbital
foramen to supply the skin of the middle third of the face. The nerve
traverses the fat of the inferior orbital fissure just proximal to the canal
and exits the infraorbital canal into a small amount of fat adjacent to the
anterior surface of the maxilla at the infraorbital foramen. This fat is deep
relative to the levator labii superioris muscle between the muscle and the
anterior surface of the maxilla at the level of the foramen.
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Fig. 2. —Drawing shows anterior view of orbit and infraorbital canal
and foramen. IOF = inferior orbital fissure, SOF = superior orbital fissure,
FR = foramen rotundum, IC = infraorbital canal, IF = infraorbital foramen.
(Modified with permission from
[5])
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The superior alveolar nerve passes through the fat along the posterior
aspect of the posterior wall of the maxillary sinus and perforates the bone in
several places to supply most of the maxillary teeth. The fat along the
posterior aspect of the sinus wall has been called the "retromaxillary
fat."
Another small branch of the maxillary nerve, called the "zygomatic
nerve," runs into the orbit through the inferior orbital fissure. The
nerve runs along the lateral wall of the orbit and reaches the skin of the
temporal region and the lateral cheek
[8].
The greater palatine nerve runs inferiorly from the pterygopalatine fossa
through the pterygopalatine canal and exits the greater palatine foramen to
reach the soft tissue covering the hard palate. The greater palatine foramen
is located in palatine bone, distal to the third maxillary molar
(Fig. 3). A small amount of fat
squeezes into the greater palatine foramen and surrounds the nerve at that
point.
Appearance of the Juxtaforaminal Fat Pads
The normal appearance of juxtaforaminal fat pads along the second division
of the trigeminal nerve pathways is shown in order in Figures
4,
5A,
5B,
6A,
6B,
6C,
6D,
6E,
6F,
7A,
7B,
7C,
7D,
7E,
7F,
7G. The foramina and fissures
can be recognized on bone algorithm CT (Figs.
4,
6B,
6C,
6D,
6E, and
7A,
7B,
7C,
7D). The fat pads adjacent to
them are obvious on both CT and MRI. The normal finding for the fat is low
density on CT (Figs. 5A,
5B,
6A,
6F,
7E, and
7F) and high signal intensity
on T1-weighted images (Fig.
7G).
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Fig. 5A. —Pterygopalatine fossa in adult without evidence of cancer.
Contrast-enhanced axial CT scan shows pterygopalatine fossa (arrows)
between posterior wall of maxillary sinus and anterior surface of pterygoid
process of sphenoid bone. Fossa is seen as low density because of contained
fat.
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Fig. 6A. —Inferior orbital fissure, infraorbital canal, and
infraorbital foramen in adult without evidence of cancer. Contrast-enhanced
axial CT scan shows level of inferior orbital fissure. Infraorbital nerve
continues along inferior orbital fissure and passes through small amount of
fat (arrows) at entrance to infraorbital canal.
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Fig. 6B. —Inferior orbital fissure, infraorbital canal, and
infraorbital foramen in adult without evidence of cancer. Bone algorithm axial
CT scan shows infraorbital canal and entrance to canal (arrow). Nerve
follows infraorbital canal (arrowheads) along floor of orbit.
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Fig. 6C. —Inferior orbital fissure, infraorbital canal, and
infraorbital foramen in adult without evidence of cancer. Bone algorithm
coronal CT scan shows infraorbital canals or grooves (arrows).
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Fig. 6D. —Inferior orbital fissure, infraorbital canal, and
infraorbital foramen in adult without evidence of cancer. Bone algorithm
sagittal CT scan shows infraorbital canal (arrows) running along
floor of orbit and opening at infraorbital foramen.
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Fig. 6E. —Inferior orbital fissure, infraorbital canal, and
infraorbital foramen in adult without evidence of cancer. Bone algorithm axial
CT scan obtained through infraorbital foramina shows osseous opening
(arrow).
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Fig. 6F. —Inferior orbital fissure, infraorbital canal, and
infraorbital foramen in adult without evidence of cancer. Unenhanced axial CT
scan shows fat bulging into infraorbital foramen (arrow).
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Fig. 7A. —Pterygopalatine canal and greater palatine foramen in adult
without evidence of cancer. Bone algorithm coronal CT scan shows
pterygopalatine canal (arrows), which carries nerve from
pterygopalatine fossa to greater palatine foramen.
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Fig. 7C. —Pterygopalatine canal and greater palatine foramen in adult
without evidence of cancer. Bone algorithm axial CT scan shows greater
palatine foramen (arrows) in posterolateral palatal region.
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Fig. 7D. —Pterygopalatine canal and greater palatine foramen in adult
without evidence of cancer. Bone algorithm coronal CT scan shows greater
palatine foramen, which opens (arrow) to submucosa of roof of
mouth.
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Fig. 7E. —Pterygopalatine canal and greater palatine foramen in adult
without evidence of cancer. Unenhanced axial CT scan shows low density because
of fat (arrowhead) in greater palatine foramen.
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Fig. 7G. —Pterygopalatine canal and greater palatine foramen in adult
without evidence of cancer. Coronal T1-weighted image shows high-intensity fat
(arrowhead). Note minor salivary glands (arrows) between
bone and mucosa.
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Obliteration of Fat and Perineural Tumor Spread
Perineural tumor spread is a critical issue for treatment and prognosis.
Although perineural spread along the trigeminal nerve can present as facial
pain, the phenomenon is often silent and thus imaging plays a crucial role
[9]. Tumor consistently has an
appearance different from that of fat on either CT or MRI. Obliteration of the
juxtaforaminal fat is a sensitive finding for detecting tumor spread. The
tumor can be detected because it infiltrates the fat or enlarges the nerve,
compressing or displacing the fat (Figs.
8A,
8B,
8C,
8D,
8E and
9A,
9B,
9C,
9D). Alternatively, depiction
of the normal fat is a reassuring finding, indicating that the tumor has not
reached the level of the associated foramen.
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Fig. 8A. —79-year-old woman with lymphoma in right face.
Contrast-enhanced axial CT scan shows abnormal soft tissue in right
infraorbital region (arrow). Note obliteration of fat at infraorbital
foramen (white arrowhead). Fat in pterygopalatine fossa (black
arrowhead) is also obliterated.
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Fig. 8C. —79-year-old woman with lymphoma in right face. Sagittal
T1-weighted image shows tumor in premaxillary soft tissues
(arrowhead). Tumor follows and enlarges infraorbital canal (large
arrow). Compare this appearance with that of normal infraorbital nerve
(small arrow) of opposite noninvolved side shown in right side of
figure.
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Fig. 9A. —60-year-old man with lymphoma in left pterygopalatine fossa.
Contrast-enhanced axial CT scan shows obliteration of fat in pterygopalatine
fossa (arrow). Tumor obliterates fat at posterior opening of
infraorbital canal (arrowhead) and follows infraorbital nerve
anteriorly and foramen rotundum posteriorly.
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Fig. 9B. —60-year-old man with lymphoma in left pterygopalatine fossa.
Coronal T1-weighted image shows that tumor extends through infraorbital canal
(arrow). Tumor in palate obliterates fat in greater palatine foramen
of left side. Compare with opposite side (arrowheads).
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Fig. 9C. —60-year-old man with lymphoma in left pterygopalatine fossa.
Contrast-enhanced axial CT scan shows obliterated fat in greater palatine
foramen (arrowhead). Compare with opposite side (arrow).
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Fig. 9D. —60-year-old man with lymphoma in left pterygopalatine fossa.
Contrast-enhanced coronal CT scan also shows obliteration of fat in greater
palatine foramen (arrowhead). Compare with opposite side
(arrow).
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Adenoid cystic carcinoma characteristically exhibits perineural spread.
Many adenoid cystic carcinomas arise in the minor salivary glands found along
the posterior palate at the roof of the mouth. The obliteration of the fat pad
at the greater palatine foramen raises the question of perineural spread from
the tumor arising at that location. If the fat is intact, perineural spread is
much less likely.
In the same manner, the obliteration of the fat pad at the entrance to the
infraorbital foramen is sensitive for the detection of perineural spread along
the infraorbital nerve from carcinoma or melanoma arising from the skin in the
middle face or from carcinoma of the lip.
The integrity or obliteration of fat should be examined not only along the
course of the nerve extending toward the skull base but also along the course
of other branches of the nerve leading away from the skull base. For example,
tumor can grow distally along a nerve after it reaches a branch point in the
pterygopalatine fossa (Fig.
9A,
9B,
9C,
9D). A tumor growing
superiorly along the greater palatine nerve reaches the pterygopalatine fossa,
from which growth can proceed centrally through the foramen rotundum but can
also spread peripherally along the infraorbital nerve. Similarly, a tumor
growing into Meckel's cave following one branch of the nerve can grow back out
of the skull base following another. Tumor has been reported to extend along
the nerve without enlargement and resurface in distant locations along the
neural pathways [4,
5]. These skipped areas should
be considered, although this phenomenon is unusual. The radiologist should
examine the entire pathway of an involved nerve.
Conclusion
Obliteration of the normal fat is a key finding in the detection of
perineural spread. Juxtaforaminal fat pads are identified on CT and MRI at the
peripheral foramina and the major foramina and are useful in assessing
potential perineural spread.
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Introduction
The Pathway of the...
